Maximum permissible measurement error. Measurement errors
Sources of errors (instrumental and methodological errors, the influence of interference, subjective errors). Nominal and real conversion function, absolute and relative error of the measuring instrument, basic and additional errors. Limits of permissible errors, accuracy classes of measuring instruments. Identification and reduction of systematic errors. Estimation of random errors. Confidence interval and confidence level. Estimation of errors of indirect measurements. Processing of measurement results. [ 1 : p.23 ... 35,40,41,53,54,56 ... 61; 2 : p.22 ... 53; 3 : p. 48 ... 91; 4 : p.21,22,35 ... 52,63 ... 71, 72 ... 77,85 ... 93].
II.1. Basic information and guidelines.
One of the fundamental concepts of Metrology is the concept of measurement error.
Measurement error is the deviation of the measured
the value of a physical quantity from its true value.
The measurement error, in general, can be caused by the following reasons:
Imperfection of the principle of operation and insufficient quality of elements of the used measuring instrument.
The imperfection of the measurement method and the influence of the measuring instrument used on the measured value itself, depending on the method of using this measuring instrument.
Subjective errors of the experimenter.
Since the true value of the measured quantity is never known (otherwise there is no need for measurements), the numerical value of the measurement error can be found only approximately. The closest to the true value of the measured quantity is the value that can be obtained using standard measuring instruments (measuring instruments of the highest accuracy). We agreed to call this value valid measured value. The actual value is also inaccurate, however, due to the small error of standard measuring instruments, the error in determining the actual value is neglected.
Error classification
According to the form of presentation, the concepts of absolute measurement error and relative measurement error are distinguished.
Absolute error measurements are called the difference between
measured and actual values of the measured
quantities:
where ∆ is the absolute error,
- measured value,
- the actual value of the measured value.
The absolute error has the dimension of the measured value. The sign of the absolute error will be positive if the measured value is greater than the actual value, and negative otherwise.
Relative error called the ratio of absolute
errors to the actual value of the measured value:
where δ is the relative error.
Most often, the relative error is determined approximately as a percentage of the measured value:
The relative error shows how much (in%) of the measured value is the absolute error. The relative error allows more clearly than the absolute error to judge the accuracy of the measured value.
According to the sources of origin, errors are divided into the following types:
Instrumental errors;
Methodological errors;
Subjective errors made by the experimenter.
Instrumental the errors that belong to this type of measuring instruments are called, can be determined during their tests and entered in the passport of the measuring instrument in the form of the limits of permissible errors.
The instrumental error arises from the imperfection of the principle of operation and the insufficiently high quality of the elements used in the design of the measuring instrument. For this reason, the actual transfer characteristic of each copy of the measuring instrument differs to a greater or lesser extent from the nominal (calculated) transfer characteristic. The difference between the real characteristics of the measuring instrument and the nominal one (Fig. 1) determines the value of the instrumental error of the measuring instrument.
Fig. 1. Illustration for the definition of the concept of instrumental
errors.
Here: 1 - nominal characteristic of the measuring instrument;
2 - the real characteristic of the measuring instrument.
As can be seen from Fig. 1, when the measured value changes, the instrumental error can have different values (both positive and negative).
When creating measuring instruments of any physical quantity, unfortunately, it is not possible to completely get rid of the reaction of this measuring instrument to changes in other (not measured) quantities. Along with the sensitivity of the measuring instrument to the measured value, it always reacts (albeit to a much lesser extent) to changes in operating conditions. For this reason, the instrumental error is subdivided into the main error and additional errors.
The main error is called the error occurring
in the case of using a measuring instrument under normal conditions
exploitation.
The nomenclature of the quantities influencing the measuring instrument and the ranges of their variation are determined by the developers as normal conditions for each type of measuring instrument. Normal operating conditions are always indicated in the technical passport of the measuring instrument. If the experiment is carried out under conditions other than normal for a given measuring instrument, its real characteristic is distorted more than under normal conditions. Errors that arise in this case are called additional.
Additional error call the error of funds
measurements that occur under conditions other than
normal conditions, but within the acceptable work area
exploitation.
The operating conditions of operation, as well as the normal ones, are mandatory given in the technical passport of the measuring instruments.
The instrumental error of measuring instruments of a certain type should not exceed a certain specified value - the so-called maximum permissible basic error of measuring instruments of this type. The actual basic error of each specific specimen of this type is at the same time a random variable and can take different values, sometimes even equal to zero, but in any case, the instrumental error should not exceed the specified limit value. If this condition is not met, the measuring instrument should be withdrawn from circulation.
Methodological are the errors that arise due to the unsuccessful choice of the measuring instrument by the experimenter to solve the problem. They cannot be attributed to a measuring instrument and are listed in its passport.
Methodological measurement errors depend both on the characteristics of the used measuring instrument and, in many respects, on the parameters of the measurement object itself. Poorly chosen measuring instruments can distort the state of the measurement object. In this case, the methodical component of the error may turn out to be significantly larger than the instrumental one.
Subjective errors are called errors,
allowed by the experimenter himself when conducting
measurements.
This type of error is usually associated with the experimenter's carelessness: using the device without eliminating the zero offset, incorrect determination of the scale division value, inaccurate counting of the division fraction, connection errors, etc.
By the nature of the manifestation, measurement errors are divided into:
Systematic errors;
Random errors;
Blunders (blunders).
A systematic is called an error that, upon repeated measurements of the same quantity, remains constant, or changes regularly.
Systematic errors are caused both by the imperfection of the measurement method and the influence of the measuring instrument on the measured object, and by the deviation of the actual transfer characteristic of the used measuring instrument from the nominal characteristic.
Permanent systematic errors of measuring instruments can be identified and numerically determined by comparing their readings with the readings of standard measuring instruments. Such systematic errors can be reduced by adjusting the instruments or by introducing appropriate corrections. It should be noted that it is not possible to completely eliminate systematic errors of measuring instruments, since their real transfer characteristics change with changing operating conditions. In addition, there are always so-called progressive errors (increasing or decreasing) caused by the aging of the elements of the measuring instruments. Progressive errors can only be corrected by adjusting or introducing corrections for a short time.
Thus, even after adjustment or introduction of corrections, there is always a so-called non-excluded systematic error in the measurement result.
Random is called the error, which, when repeated measurements of the same quantity, takes on different values.
Random errors are due to the chaotic nature of the changes physical quantities(interference) affecting the transfer characteristic of the measuring instrument, the summation of disturbances with the measured value, as well as the presence of intrinsic noise of the measuring instrument. When creating measuring instruments, special measures of protection against interference are provided: shielding of input circuits, the use of filters, the use of stabilized supply voltage sources, etc. This allows you to reduce the amount of random errors in measurements. As a rule, with repeated measurements of the same quantity, the measurement results either coincide or differ by one or two units of the least significant digit. In such a situation, the random error is neglected and only the magnitude of the non-excluded systematic error is estimated.
The strongest random errors appear when measuring small values of physical quantities. To increase the accuracy in such cases, multiple measurements are made with subsequent statistical processing of the results by methods of probability theory and mathematical statistics.
Misses are called gross errors that significantly exceed the expected errors under given measurement conditions.
Slips mostly arise from subjective errors of the experimenter or from malfunctions of the measuring instrument during sudden changes in operating conditions (surges or dips of the mains voltage, lightning discharges, etc.) Usually, slips are easily detected during repeated measurements and are excluded from consideration ...
Estimation of errors of indirect measurements.
With indirect measurements, the measurement result is determined by the functional dependence on the results of direct measurements. Therefore, the error of indirect measurements is defined as the total differential of this function from the quantities measured using direct measurements.
;
Where: 
- the maximum absolute errors of the results of straight lines
measurements;
is the limiting absolute error of the indirect result
measurements;
- the corresponding limiting relative errors.
- functional relationship between the desired measured value and
quantities subject to direct measurements.
Statistical processing of measurement results
Due to the influence on the measuring instrument of disturbances of various origins (temperature change the environment, electromagnetic fields, vibrations, changes in the frequency and amplitude of the mains voltage, changes in atmospheric pressure, humidity, etc.), as well as due to the presence of intrinsic noise of the elements that make up the measuring instruments, the results of repeated measurements of the same physical quantity (especially its small values) will differ to a greater or lesser extent from each other. In this case, the measurement result is a random variable, which is characterized by the most probable value and the scatter (scatter) of the repeated measurements near the most probable value. If, during repeated measurements of the same quantity, the measurement results do not differ from each other, this means that the resolution of the reading device does not allow detecting this phenomenon. In this case, the random component of the measurement error is insignificant and can be neglected. In this case, the non-excluded systematic error of the measurement result is estimated by the value of the limits of the permissible errors of the used measuring instruments. If, during repeated measurements of the same quantity, a scatter of readings is observed, this means that along with a greater or lesser non-excluded systematic error, there is also a random error, which takes different values during repeated measurements.
To determine the most probable value of the measured quantity in the presence of random errors and to estimate the error with which this most probable value is determined, statistical processing of the measurement results is used. Statistical processing of the results of a series of measurements during experiments allows solving the following problems.
Determine the measurement result more accurately by averaging individual observations.
Estimate the area of uncertainty of the refined measurement result.
The main meaning of the averaging of the measurement results is that the found averaged estimate has a smaller random error than the individual results for which this averaged estimate is determined. Consequently, averaging does not completely eliminate the random nature of the averaged result, but only reduces the bandwidth of its uncertainty.
Thus, during statistical processing, first of all, the most probable value of the measured value is determined by calculating the arithmetic mean of all readings:
where: x i - the result of the i-th measurement;
n is the number of measurements performed in a given series of measurements.
After that, the deviation of the results of individual measurements x i from this estimate of the mean value is evaluated 
;
.
Then an estimate of the standard deviation is found 
observations, characterizing the degree of scattering of the results of individual observations near 
, according to the formula:
.
Accuracy of estimation of the most probable value of the measured quantity 
depends on the number of observations 
... It is easy to verify that the results of several estimates 
for the same number 
individual measurements will differ. Thus, the assessment itself 
is also a random variable. In this regard, an estimate of the standard deviation of the measurement result is calculated 
, which is denoted 
... This estimate characterizes the degree of dispersion of values 
in relation to the true value of the result, i.e. characterizes the accuracy of the result obtained by averaging the result of multiple measurements. Therefore, according to 
the systematic component of the result of a series of measurements can be estimated. For various 
it is determined by the formula:
Consequently, the accuracy of the result of multiple measurements increases with the number of the latter.
However, in most practical cases, it is important for us to determine not just the degree of dispersion of the error value during a series of measurements (i.e., the value 
), and estimate the probability of a measurement error not exceeding the permissible one, i.e. not exceeding the limits of a certain specified range of scatter of the resulting errors.
Confidence interval
called the interval, which with a given probability, called confidence level
covers the true value of the measured value.
When determining the confidence intervals, it is necessary, first of all, to take into account that the distribution law of errors obtained when carrying out multiple measurements, when the number of measurements in a series is less than 30, is described not by the normal distribution law, but by the so-called Student's distribution law. And, in these cases, the value of the confidence interval is usually estimated by the formula:
,
where 
- the so-called Student's coefficient.
Table 4.1 shows the values of the Student's coefficients 
depending on the specified confidence level and the number of observations 
... When making measurements, they are usually given a confidence level of 0.95 or 0.99.
Table 4.1
Values of Student's coefficients 
.
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When studying the materials in this section, it should be well understood that the errors in the measurement results and the errors in measuring instruments are not identical concepts. The error of a measuring instrument is its property, a characteristic, for the description of which a number of rules are used, enshrined in standards and regulatory documents. This is the fraction of the measurement error that is determined only by the measuring instrument itself. The measurement error (measurement result) is a number that characterizes the uncertainty limits of the value of the measured quantity. In addition to the error of the measuring instrument, it may include error components generated by the used measurement method (methodological errors), the action of influencing (unmeasured) quantities, reading error, etc.
Standardization of errors of measuring instruments.
The SI accuracy is determined by the maximum permissible errors that can be obtained when using it.
The standardization of errors of measuring instruments is called
the procedure for assigning admissible boundaries is
additional errors, as well as the choice of the form of indication
these boundaries in the normative and technical documentation.
The limits of the permissible basic and additional errors are determined by the developers for each type of measuring instruments at the stage of production preparation. Depending on the purpose of the measuring instrument and the nature of the error change within the measurement range, either the maximum permissible value of the basic absolute error, or the maximum permissible value of the basic reduced error, or the maximum permissible value of the basic relative error is standardized for measuring instruments of various types.
For each type of measuring instrument, the nature of the change in the error within the measurement range depends on the principle of operation of this measuring instrument and can be very diverse. However, as practice has shown, among this variety it is often possible to distinguish three typical cases that predetermine the choice of the form of representation of the limits of the permissible error. Typical variants of the deviation of the real transfer characteristics of measuring instruments from the nominal characteristics and the corresponding graphs of changes in the limiting values of the absolute and relative errors depending on the measured value are shown in Fig. 2.
If the real transfer characteristic of the measuring instrument is displaced with respect to the nominal one (1st graph in Fig. 2a), the absolute error arising in this case (1st graph in Fig. 2b) does not depend on the measured value.
The component of the error of the measuring instrument, which does not depend on the measured value, is calledadditive error.
If the angle of inclination of the actual transfer characteristic of the measuring instrument differs from the nominal one (2nd graph in Fig.2a), then the absolute error will linearly depend on the measured value (2nd graph in Fig.2b).
The component of the error of the measuring instrument, linearly dependent on the measured value, is calledmultiplicative error.
If the real transfer characteristic of the measuring instrument is displaced with respect to the nominal one and the angle of its inclination differs from the nominal one (3rd graph in Fig. 2a), then in this case there is both an additive and a multiplicative error.
An additive error arises due to inaccurate setting of the zero value before the start of measurements, zero drift during measurements, due to the presence of friction in the supports of the measuring mechanism, due to the presence of thermo-emf in contact connections, etc.
The multiplicative error occurs when the gain or attenuation of the input signals changes (for example, when the ambient temperature changes, or due to aging of elements), due to changes in the values reproduced by the measures built into the measuring instruments, due to changes in the stiffness of the springs that create a counter torque in electromechanical devices, etc.
The width of the uncertainty band of the values of the absolute (Fig. 2b) and relative (Fig. 2c) errors characterizes the spread and change during operation of the individual characteristics of the set of measuring instruments of a certain type in circulation.
A) Normalization of the limits of the permissible basic error for
measuring instruments with a predominant additive error.
For measuring instruments with a predominant additive error (1st graph in Fig. 2), it is convenient to normalize by one number the maximum permissible value of the absolute error (∆ max = ± a). In this case, the actual absolute error ∆ of each instance of a measuring instrument of this type in different parts of the scale may have different values, but should not exceed the maximum permissible value (∆ ≤ ± a). In multi-limit measuring devices with a predominant additive error, each measurement limit would have to indicate its value of the maximum permissible absolute error. Unfortunately, as can be seen from the 1st graph in Fig. 2c, it is not possible to normalize the limit of the permissible relative error at different points of the scale by one number. For this reason, for measuring instruments with a predominant additive error, the value of the so-called basic given relative error
,
where X N is a normalizing value.
In this way, for example, the errors of most electromechanical and electronic devices with dial indicators are normalized. As a normalizing value X N, the measurement limit (X N = X max), twice the value of the measurement limit (if the zero mark is in the middle of the scale), or the length of the scale (for instruments with an uneven scale) are usually used. If X N = X max, then the value of the reduced error γ is equal to the limit of the permissible relative error of the measuring instrument at the point corresponding to the measurement limit. For a given value of the limit of the permissible basic reduced error, it is easy to determine the limit of the permissible basic absolute error for each measurement limit of a multi-limit device: 
.
After that, for any mark on the X scale, an estimate of the maximum permissible basic relative error can be made:
.
B) Standardization of the limits of the permissible basic error for
measuring instruments with a predominant multiplicative
error.
As can be seen from Fig. 2 (2nd graph), for measuring instruments with a predominant multiplicative error, it is convenient to normalize the limit of the permissible basic relative error by one number (Fig. 2c) δ max = ± b ∙ 100%. In this case, the actual relative error of each instance of a measuring instrument of this type in different parts of the scale may have different values, but should not exceed the maximum permissible value (δ ≤ ± b ∙ 100%). For a given value of the maximum permissible relative error δ max for any point on the scale, an assessment of the maximum permissible absolute error can be made:
.
The majority of multi-valued measures, electric energy meters, water meters, flow meters, etc. are among the measuring instruments with a predominant multiplicative error. It should be noted that for real measuring instruments with a prevailing multiplicative error, it is not possible to completely eliminate the additive error. For this reason, the technical documentation always indicates the smallest value of the measured value, for which the limit of the permissible basic relative error does not yet exceed the specified value δ max. Below this smallest value of the measured quantity, the measurement error is not standardized and is uncertain.
C) Standardization of the limits of the permissible basic error for
measuring instruments with comparable additive and multiplicative
error.
If the additive and multiplicative components of the error of the measuring instrument are comparable (3rd graph in Fig. 2), then setting the maximum permissible error in one number is not possible. In this case, either the limit of the permissible absolute basic error is normalized (the maximum permissible values of a and b are indicated), or (most often) the limit of the permissible relative basic error is normalized. IN the latter case numerical values of maximum permissible relative errors at different points of the scale are estimated by the formula:
,
where X max is the measurement limit;
X is the measured value;
d = 
- the value reduced to the measurement limit
additive component of the basic error;
c = 
- the value of the resulting relative
basic error at the point corresponding to the limit
measurements.
By the method considered above (indicating the numerical values of c and d), in particular, the maximum permissible values of the relative basic error of digital measuring instruments are normalized. In this case, the relative errors of each instance of measuring instruments of a certain type should not exceed the values of the maximum permissible error established for this type of measuring instruments:
.
In this case, the absolute basic error is determined by the formula
.
D) Standardization of additional errors.
Most often, the limits of permissible additional errors are indicated in the technical documentation either by one value for the entire working area of the quantity that affects the accuracy of the measuring instrument (sometimes by several values for the subranges of the working area of the influencing quantity), or by the ratio of the limit of the permissible additional error to the interval of values of the influencing quantity. The limits of permissible additional errors are indicated on each value affecting the accuracy of the measuring instrument. In this case, as a rule, the values of additional errors are set in the form of a fractional or multiple value of the limit of the permissible basic error. For example, the documentation may indicate that at ambient temperatures outside the normal temperature range, the limit of the additional permissible error arising from this reason should not exceed 
0.2% at 10 o C.
Accuracy classes of measuring instruments.
Historically, according to accuracy, measuring instruments are divided into classes. Sometimes they are called accuracy classes, sometimes tolerance classes, sometimes just classes.
Accuracy class of measuring instrument - this is its characteristic, reflecting the precision capabilities of measuring instruments of this type.
Alphabetic or numerical designation of accuracy classes is allowed. Measuring instruments designed to measure two or more physical quantities may be assigned different classes accuracy for each measured value. Measuring instruments with two or more switchable measuring ranges are also allowed to be assigned two or more accuracy classes.
If the limit of the permissible absolute basic error is normalized, or different values of the limits of the permissible relative basic error are set in different sub-ranges of measurements, then, as a rule, the letter designation of the classes is used. So, for example, platinum resistance thermometers are manufactured with a tolerance class BUT or tolerance class IN. Moreover, for the class BUT the limit of the permissible absolute basic error is set, and for the class IN- , where 
- temperature of the measured medium.
If for measuring instruments of a particular type, one value of the maximum permissible reduced basic error is normalized, or one value of the maximum permissible relative basic error, or the values c and d, then decimal numbers are used to denote precision classes. In accordance with GOST 8.401-80, the following numbers can be used to designate accuracy classes:
1 ∙ 10 n; 1.5 ∙ 10 n; 2 ∙ 10 n; 2.5 ∙ 10 n; 4 ∙ 10 n; 5 ∙ 10 n; 6 ∙ 10 n, where n = 0, -1, -2, etc.
For measuring instruments with a predominant additive error, the numerical value of the accuracy class is selected from the specified range equal to the maximum permissible value of the reduced basic error, expressed as a percentage. For measuring instruments with a predominant multiplicative error, the numerical value of the accuracy class corresponds to the limit of the permissible relative basic error, also expressed as a percentage. For measuring instruments with commensurate additive and multiplicative errors, the number with and d are also selected from the above range. In this case, the accuracy class of the measuring instrument is indicated by two numbers separated by a slash, for example, 0.05 / 0.02. In this case c = 0,05%; d = 0.02%. Examples of designations of accuracy classes in documentation and on measuring instruments, as well as calculation formulas for assessing the limits of the permissible basic error are given in Table 1.
Rules for rounding and recording the measurement result.
The normalization of the limits of permissible errors of measuring instruments is carried out by indicating the value of the errors with one or two significant digits. For this reason, only the first one or two significant digits should be left in the calculation of the measurement uncertainties. The following rules are used for rounding:
The error of the measurement result is indicated by two significant figures, if the first of them is not more than 2, and by one figure, if the first of them is 3 or more.
The reading is rounded off to the same decimal place as the rounded absolute error.
Rounding is done in the final answer, intermediate calculations are performed with one or two redundant digits.
The reading of the device is 5.361 V;
The calculated value of the absolute error is ± 0.264 V;
The rounded off value of the absolute error is ± 0.26 V;
The measurement result is (5.36 ± 0.26) V.
Table 1
Examples of designation of accuracy classes of measuring instruments and calculated
formulas for assessing the limits of the permissible basic error.
|
representation standardized basic inaccuracies |
Examples of designation accuracy class |
Calculation formulas for assessing limits permissible basic inaccuracies |
Notes (edit) |
|
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documentation |
means measurements |
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Normalized limit of permissible absolute basic error |
The options are: Class B; Tolerance class IN; - accuracy class IN. |
|
The values a and b are given in documentation on the means measurements. |
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Normalized limit of permissible given basic error |
The options are: Accuracy class 1.5 Not indicated. |
|
For appliances with uniform scale and zero mark in the beginning of the scale |
|
|
The options are: Accuracy class 2.5; Not indicated |
|
For appliances with uneven scale. Scale length indicated in documentation. |
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Normalized limit of permissible relative basic error |
Accuracy class 0.5. |
|
For measuring instruments with predominant multiplicative error. |
|
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The options are: Accuracy class Not indicated. |
0,02/0,01 |
|
For measuring instruments with commensurate additive and multiplicative error |
|
or 
or 
where 
measurement limit.
- the limit of the permissible absolute error in mm.
- the length of the entire scale.
The reading of the device is 35.67 mA;
The calculated value of the absolute error is ± 0.541 mA;
The rounded off value of the absolute error is ± 0.5 mA;
The measurement result is (35.7 ± 0.5) mA.
The calculated value of the relative error is ± 1.268%;
The rounded off value is ± 1.3%.
The calculated value of the relative error is ± 0.367%;
The rounded off value of the relative error is ± 0.4%.
II.2. Self-test questions
What causes measurement errors?
List the types of errors that arise in the measurement process?
What is the difference between absolute, relative and reduced measurement errors and what is the point of their introduction?
What is the difference between the basic measurement error and the additional one?
What is the difference between the methodical measurement error and the instrumental error?
What is the difference between a systematic measurement error and a random one?
What is meant by additive and multiplicative leaving errors?
When is it advisable to use statistical processing of measurement results?
What statistical characteristics of processing are most commonly used in practice?
How is the non-excluded systematic error estimated in the statistical processing of measurement results?
11. What characterizes the value of the standard deviation?
12. What is the essence of the concepts of "confidence probability" and "confidence interval" used in the statistical processing of measurement results?
13. What is the difference between the concepts of "measurement error" and
"Measuring instrument error"?
The error is one of the most important metrological characteristics of a measuring instrument (technical means intended for measurements). It corresponds to the difference between the readings of the measuring instrument and the true value of the measured quantity. The smaller the error, the more accurate the measuring instrument is considered, the higher its quality. The largest possible error value for a certain type of measuring instrument under certain conditions (for example, in a given range of values of the measured quantity) is called the permissible error limit. Usually set the limits of the permissible error, i.e. bottom and upper bound intervals beyond which the error should not go.
It is customary to express both the errors themselves and their limits in the form of absolute, relative or reduced errors. The specific form is chosen depending on the nature of the change in errors within the measurement range, as well as on the conditions of use and purpose of measuring instruments. The absolute error is indicated in the units of the measured value, and the relative and reduced - usually in percent. The relative error can characterize the quality of the measuring instrument much more accurately than the given one, which will be discussed in more detail below.
The relationship between the absolute (Δ), relative (δ) and reduced (γ) errors is determined by the formulas:
where X is the value of the measured quantity, X N is the normalizing value, expressed in the same units as Δ. The criteria for choosing the standardizing value X N are established by GOST 8.401-80 depending on the properties of the measuring instrument, and usually it should be equal to the measurement limit (X K), i.e.
The limits of permissible errors are recommended to be expressed in the form given if the error limits can be assumed to be practically unchanged within the measurement range (for example, for analogue voltmeters, when the error limits are determined depending on the scale division value, regardless of the measured voltage value). Otherwise, it is recommended to express the limits of permissible errors in the form of relative ones according to GOST 8.401-80.
However, in practice, the expression of the limits of permissible errors in the form of reduced errors is erroneously used in cases where the error limits cannot be assumed to be constant within the measurement range. This either misleads users (when they do not understand that the error specified in this way as a percentage is not considered at all from the measured value), or significantly limits the scope of the measuring instrument, because formally, in this case, the error in relation to the measured value increases, for example, ten times if the measured value is 0.1 of the measurement limit.
Expression of the limits of permissible errors in the form of relative errors makes it possible to accurately take into account the real dependence of the error limits on the value of the measured quantity when using a formula of the form
δ = ±
where c and d are coefficients, d At the same time, at the point X = X k, the limits of the permissible relative error, calculated by the formula (4), will coincide with the limits of the permissible reduced error At points X Δ 1 = δ X = X Δ 2 = γ X K = c X k Those. in a wide range of values of the measured value, a much higher measurement accuracy can be ensured if we normalize not the limits of the permissible reduced error according to formula (5), but the limits of the permissible relative error according to formula (4). This means, for example, that for a measuring converter based on an ADC with a large digit capacity and a large dynamic range of the signal, the expression of the error limits in the form of a relative describes more adequately the real limits of the converter error, in comparison with the form given. This terminology is widely used when describing the metrological characteristics of various Measuring Instruments, for example, those listed below manufactured by LLC "L Card": ADC / DAC module Error
Is the deviation of the measurement result from the true value of the measured value. The true value of PV can be established only by carrying out an infinite number of measurements, which is impossible to implement in practice. The true value of the measured quantity is unattainable, and for the analysis of errors, the actual value of the measured quantity is used as the closest to the true value, the value is obtained using the most advanced measurement method and the most high-precision measuring instruments. Thus, the measurement error is a deviation from the actual value ∆ = Xd - Xmeas The error accompanies all measurements and is associated with the imperfection of the method, measuring instrument, measurement conditions (when they differ from standard conditions). Depending on the principles of operation of the device, certain factors have an impact. Distinguish between the errors of the SI and the measurement result due to the influence of external conditions, the features of the measured value, the imperfection of the SI. The error of the measurement result includes the error and measuring instruments, as well as the influence of the measurement conditions, the properties of the object and the measured value ∆ri = ∆si + ∆vu + ∆m.o + ∆siv. Error classification: 1) By way of expression: a) Absolute- error, expressed in units of the measured value ∆ = Xd-Xism b) Relative- error, expressed as the ratio of the absolute error to the measurement result or the actual value of the measured value γrel = (∆ / Xd) * 100. c) The given Is the relative error, expressed by the ratio of the absolute error of the measuring instrument to the condition, the accepted value of the quantity constant in the entire measurement range (or part of the range) γprev = (∆ / Xnorm) * 100, where Xnorm is the normalizing value established for the given values. The choice of KNorm is made in accordance with GOST 8.009-84. This can be the upper limit of the measuring instrument, the measuring range, the length of the scale, etc. For a variety of measuring instruments, the accuracy class is established according to the reduced error. The reduced error is introduced because the relative characterizes the error only at a given point of the scale and depends on the value of the measured value. 2) For reasons and conditions of occurrence: a) The main- this is the error of measuring instruments, which are in normal operating conditions, arises from the imperfection of the conversion function and, in general, the imperfection of the properties of the measuring instruments and reflects the difference in the actual function of converting the measuring instruments to standard conditions. from the nominal standardized documents for measuring instruments (standards, technical conditions). Regulatory documents provide for the following n.o .: Measurement operating conditions- these are the conditions under which the values of the influencing quantities are within the working areas, for which the additional error or change in the MI readings is normalized. For example, for capacitors, an additional error associated with a deviation of temperature from normal is normalized; for the ammeter, the deviation of the alternating current frequency is 50 Hz. b) Additional Is a component of the error of measuring instruments that arises in addition to the main one, due to the deviation of any of the influencing quantities from the norm of its value or due to its going beyond the normalized range of values. Usually the largest value of the additional error is normalized. Basic permissible error limit- naib. the main error of measuring instruments, at which the measuring instrument can be suitable and approved for use according to those. conditions. Additional permissible error limit- the largest additional error at which the SI is approved for use. For example, for a device with CT 1.0, the reduced additional temperature error should not exceed ± 1% for every 10 ° temperature change. The limits of the permissible basic and additional error can be expressed in the form of absolute, relative or reduced error. In order to be able to choose SI by comparing their characteristics, introduce generalized characteristic of this type of SI - accuracy class (CT)
... Usually this is the limit of the main and additional errors allowed. CT allows you to judge the limits of the error of one type of measuring instrument, but it is not a direct indicator of the accuracy of measurements performed with the help of each of these measuring instruments, since the error also depends on the method, measurement conditions, etc. This must be taken into account when choosing a measuring instrument, depending on the specified accuracy. CT values are set in standards or in technical conditions or other regulatory documents and are selected in accordance with GOST 8.401-80 from a standard range of values. For example, for electromechanical devices: 0.05; 0.1; 0.2; 0.5; 1.0; 2.5; 4.0; 6.0. Knowing the CT SI, you can find the maximum permissible value of the absolute error for all points of the measurement range from the formula for the reduced error: ∆maxadd = (γpriv * Xnorm) / 100. CT is usually applied to the scale of the device in different forms, for example, (2.5) (in a circle). 3) By the nature of the changes: a) systematic- the component of the error that remains constant or changes according to a known pattern during the entire time of measurements. Can be excluded from measurement results by adjusting or making corrections. These include: methodical P, instrumental P, subjective P, etc. Such a quality of SI, when the systematic error is close to zero, is called correctness. b) random- these are the components of the error, changing randomly, the reasons cannot be precisely indicated, and therefore cannot be eliminated. Lead to ambiguity in readings. A decrease is possible with multiple measurements and subsequent statistical processing of the results. Those. the averaged result of multiple measurements is closer to the actual value than the result of one measurement. The quality, which is characterized by the closeness to zero of the random component of the error, is called convergence indications of this device. c) misses - gross errors associated with operator errors or unaccounted for external influences. They are usually excluded from the measurement results, not taken into account when processing the results. 4) Depending on the measured value: a) Additive errors(independent of the measured value) b) Multiplicative errors(proportional to the measured value). The multiplicative error is also called the sensitivity error. The additive error usually arises due to noise, interference, vibrations, friction in the supports. Example: zero error and discreteness (quantization) error. The multiplicative error is caused by the adjustment error of the individual elements of the measuring instruments. For example, due to aging (SI sensitivity error). Depending on which error of the device is significant, the metrological characteristics are normalized. If the additive error is significant, then the limit of the permissible basic error is normalized in the form of the reduced error. If the multiplicative error is significant, then the limit of the permissible basic error is determined by the formula of the relative error. Then the relative total error: γrel = Δ / X = γadd + γmult = γadd + γmult + γadd * Xnorm / X– γadd = ±, where c = γadd + γmult; d = γadd. This is a way of standardizing metrological characteristics when the additive and multiplicative components of the error are comparable, i.e. the limit of the relative permissible basic error is expressed in a two-term formula, respectively, and the designation CT consists of two numbers expressing c and d in%, separated by a slash. For example, 0.02 / 0.01. This is convenient because the number s is the relative error of the SI in n.o. The second term of the formula characterizes an increase in the relative measurement error with an increase in the value of X, i.e. characterizes the influence of the additive component of the error. 5) Depending on the influence of the nature of the change in the measured value: a) Static- SI error when measuring a constant or slowly changing quantity. b) Dynamic- SI error arising when measuring the PV rapidly changing in time. The dynamic error is a consequence of the inertia of the device. Vi. Requirements for performing visual and measuring control Preparation of work sites 6.1.1. Visual and measuring control is recommended to be carried out on stationary areas, which must be equipped with work tables, stands, roller supports and other means that ensure the convenience of work. 6.1.2. Visual and measuring control during installation, construction, repair, reconstruction, as well as during the operation of technical devices and structures is carried out at the place of work. In this case, the convenience of the approach of the specialists performing the control to the place of control work must be ensured, conditions for the safe production of work must be created, including, if necessary, scaffolding, fences, scaffolding, cradles, mobile towers or other auxiliary devices must be installed, providing optimal access (convenience of work) of a specialist to the controlled surface, as well as the possibility of connecting local lighting lamps with a voltage of 12 V. 6.1.3. Control areas, especially stationary ones, are recommended to be located in the most illuminated places of the workshop with natural lighting. To create an optimal contrast between the defect and the background in the test area, it is necessary to use an additional portable light source, that is, use combined lighting. The illumination of the controlled surfaces must be sufficient for reliable detection of defects, but not less than 500 Lx. 6.1.4. It is recommended to paint the surfaces of walls, ceilings, work tables and stands in areas of visual and measuring control in light colors (white, blue, yellow, light green, light gray) to increase the contrast of the controlled surfaces of parts (assembly units, products), increase the contrast sensitivity of the eye, reducing the general fatigue of the specialist performing the control. 6.1.5. Adequate vision for the eyes of the specialist must be provided to perform the inspection. The surface to be tested should be viewed at an angle of more than 30 ° to the plane of the test object and from a distance of up to 600 mm (Fig. 1). Rice. one. Visual inspection conditions Preparation for control 6.2.1. The preparation of the controlled surfaces is carried out by the departments of the organization performing work on visual and measuring control, and during the operation of technical devices and structures - by the services of the organization that owns the controlled object. The preparation of the controlled surfaces is not the responsibility of the control specialist. 6.2.2. Visual and measuring control during technical diagnostics (certification) of equipment operating under pressure should be carried out after the specified equipment has stopped operating, pressure is released, cooling, drainage, disconnected from other equipment, unless otherwise provided by the current PDD. If necessary, the internal devices must be removed, the insulating coating and lining that impede the control of the technical condition of the material and welded joints, partially or completely removed in the places specified in the Program of technical diagnostics (survey). 6.2.3. Before carrying out visual and measuring control, the surface of the object in the control zone must be cleaned to clean metal from rust, scale, dirt, paint, oil, moisture, slag, splashes of molten metal, corrosion products and other contaminants that interfere with the control (on the controlled surfaces, the presence of tarnishing colors, in cases where it is stipulated in the production and technical documentation (PDD). The cleaning zone should be determined by the normative document for the type of work or for the manufacture of the product. In the absence of requirements in the normative document, the cleaning zone for parts and welded seams should be: when cleaning the edges of parts for all types of arc, gas and resistance welding - not less than 20 mm from the outside and not less than 10 mm from the inside from the edges of the groove of the part; when cleaning the edges of parts for electroslag welding - at least 50 mm on each side of the welded joint; when cleaning the edges of the parts of corner joints of pipes [for example, welding a union (branch pipe) into a manifold, pipe or drum], the following must be cleaned: the surface around the hole in the main pipe (manifold, drum) at a distance of 15-20 mm, the surface of the hole for the part being welded the entire depth and surface of the welded (branch pipe) fitting - at a distance of at least 20 mm from the groove edge; when cleaning a steel backing ring (plate) or fusible wire insert - the entire outer surface of the backing ring (plate) and all surfaces of the fusible insert. Note. When inspecting painted objects, paint is not removed from the surface in the inspection zone, unless it is specifically stipulated in the ND and the surface of the object does not raise suspicion of cracks according to the results of visual inspection. 6.2.4. The controlled surface is cleaned in the manner specified in the relevant ND (for example, flushing, mechanical cleaning, wiping, blowing with compressed air, etc.). At the same time, the wall thickness of the controlled product should not decrease beyond the minus tolerances and there should not be defects that are inadmissible, according to ND, (risks, scratches, etc.). If necessary, surface preparation should be carried out with an intrinsically safe tool. 6.2.5. The roughness of the surfaces of parts, welded joints, cleaned under control, as well as the surface of the groove of the edges of parts (assembly units, products) prepared for welding should be no more than Ra 12.5 (Rz 80). 6.2.6. The roughness of the surfaces of products and welded joints for subsequent non-destructive testing methods depends on the testing method and should be no more than: Ra 3.2 (Rz 20) - with capillary control; Ra 10 (Rz 63) - with magnetic particle inspection; Ra 6.3 (Rz 40) - with ultrasonic testing. For other methods of non-destructive testing, the roughness of the tested surfaces of products is not regulated and is established by the PDD or production design documentation (PKD). table 2 Controlled parameters and requirements for visual and measuring control of semi-finished products Notes: 1. At least 50% of pipes (sheets) from a batch are subject to control according to p. 1-4. 2. Inspection according to claim 7 is subject to at least 10% of the length of each pipe (surface area of the sheet). 6.3.6. Visual and measuring quality control of the material of semi-finished products, blanks, parts and products is carried out in accordance with the Program (plan, instructions) of incoming control (Appendix B). Controlled parameters and methods of their control must be indicated in the Programs. The scope of control of the controlled parameters is selected in accordance with the requirements of standards, TU, ND or PDD, and in the absence of requirements for the scope of control in these documents, the scope of control is set in accordance with the requirements of this Instruction. 6.4. The procedure for performing visual and measuring control of preparation and assembly of parts for welding 6.4.1. When preparing parts for welding, it is necessary to control: the presence of marking and (or) documentation confirming the acceptance of semi-finished products, parts, assembly units and products during the incoming inspection; the presence of the material manufacturer's mark on the parts prepared for welding; the presence of mechanical removal of the heat-affected zone at the place of thermal (fire) cutting of workpieces (the need should be indicated in the design or technological documentation); the geometric shape of the processed edges, including when preparing parts with different nominal wall thicknesses; the geometric shape of the machined inner surfaces of the annular parts; shape of backing plates (rings) and fusible inserts; the presence of welding of the backing plate connector (ring), the quality of the welding seam of the backing plate (ring), as well as the presence of stripping of the welding seam of the backing plate connector (ring); cleanliness (absence of visually observed contamination, dust, corrosion products, moisture, oil, etc.) of the edges to be welded (surfacing) and adjacent surfaces, as well as areas of the material subject to non-destructive testing. 6.4.2. When assembling parts for welding, it is necessary to visually control: correct installation of backing plates (rings); correct installation of temporary technological fasteners; correct assembly and fastening of parts in assembly devices; the correct location and number of tacks and their quality; correct installation of protective gas blowing devices; correct application of the activating flux and protective flux-paste; the presence of a protective coating against splashes of molten metal on the surface of parts made of austenitic steels welded by manual arc and semi-automatic (automatic) welding with a consumable electrode in a shielding gas environment; cleanliness of edges and adjacent surfaces of parts. 6.4.3. Measurement control during preparation of parts for welding (Fig. 2) is carried out to check: dimensions of groove edges (bevel angles, thickness and width of blunting of groove edges); Note. Radii of rounding up to 1.0 mm in size at the transition points of the groove surfaces, as well as the size of the bevel of the inner edge, performed to improve the conditions for detecting lack of penetration in the root of the weld during radiographic inspection, cannot be measured. dimensions (diameter, length, cutter exit angle) of boring (expansion) of pipe ends along the inner diameter; sizes of backing plates (rings) and fusible inserts (width, thickness, bevel angles, diameter); sizes of elements of sector bends; perpendicularity of the ends of the cylindrical parts prepared for welding to their generatrices; the minimum actual wall thickness of the cylindrical part after boring along the inner diameter; the sizes of the holes for the nozzle (branch pipe) and the processing of edges in the pipe (manifold, body); the thickness and width of the lining in the lock connection; the width of the zone of mechanical cleaning of the outer and inner surfaces of the parts and the roughness of the surfaces of the edges and adjacent surfaces of the parts, including the place of cleaning the joint seam of the remaining backing plate (ring). 6.4.4. Measurement control of joints assembled for welding (Fig. 3) includes checking: weld seam sizes of temporary technological fasteners; Rice. 2. Dimensions controlled by measurement when preparing parts for welding (beginning): but - I-groove (no bevel); b - V-shaped one-sided groove; in - V-shaped double-sided groove; G, d - preparation for butt welding of parts, significantly different in thickness; e, f - preparation for welding of the tool joint; s - Y-shaped groove; and - V-shaped double bevel groove; To - deviation from the perpendicularity of the pipe end; l - preparation of nozzle edges D 10-65; m - I-groove with filler rib Rice. 2. The ending: n - cylindrical boring (distribution) of pipe ends along the inner diameter; NS - conical boring of pipes on the inner diameter; R- blunting inner edge of the pipe; with- backing remaining plate; T, y - backing steel remaining ring; f - steel underlay the remaining ring; NS - fusible wire insert; c- sector tap; h, NS, NS - reaming the hole for the union (branch pipe) in the body (pipe, manifold); Yu - preparation of edges for automatic welding in the environment protective gases * The size cannot be measured, it is provided with a cutting tool and is assessed visually. Rice. 3. Dimensions controlled when assembling the weld joint: but - butt joint; b - butt joint with the remaining backing plate (ring); in - butt lock connection; G - tee connection; d - gusset; e- overlapping compound; f - butt joint with fusible insert; and, To - corner joints of fittings; l -
connection with welded elements of temporary fasteners; m - misaligned connection axes of the choke and body; n - connection with axle misalignment in pipe corner joints; NS- connection with a fracture of the axes of cylindrical parts; R - tack joints; with, T - tee (elbow) connection the distance of the technological fastening from the groove edge and the location of fasteners along the length (perimeter) of the joint (if necessary, if the distance between adjacent fasteners is specified in the technical documentation); the size of the gap in the joint, including between the part and the backing plate (ring); the size of the offset of the edges (inner and outer) of the assembled parts; the size of the overlap of parts in the lap joint; dimensions (length, height) of tacks and their location along the length (perimeter) of the joint (if necessary, if it is stipulated in the technical documentation, also the distance between adjacent tacks); the size of the gap in the lock of the fusible wire insert; the size of the fracture of the axes of cylindrical pipe parts and planes of flat parts (sheets); the size of the misalignment of the axes of the choke and the hole in the body (pipe); the size of the misalignment (deviation) of the axes in the corner joints of pipes; dimensions of the width of the zone of application of a protective coating on the surfaces of parts; geometric (linear) dimensions of the assembly assembled for welding (in cases stipulated by the PKD). 6.4.5. Visual and measuring control of preparation and assembly of parts for welding is subject to at least 20% of parts and connections from those submitted for acceptance. The scope of selective quality control of preparation and assembly of parts for welding can be increased or decreased depending on the requirements of ND, PTD and PKD or at the request of the Customer. If deviations from the requirements of working drawings and (or) PDD are detected, which can lead to a deterioration in the quality of welded joints, the volume of sampling should be doubled for a group of similar parts (joints). If, during additional control, deviations from the requirements of the design documentation and (or) PDD are revealed for the second time, then the scope of control for a group of parts prepared for acceptance should be increased to 100%. Parts rejected during inspection are subject to correction. Connections of parts assembled for welding, rejected during inspection, are subject to disassembly with subsequent reassembly after elimination of the causes that caused their initial poor-quality assembly. 6.4.6. Visual control of the removal of material subjected to thermal influence during cutting by thermal methods (gas, air-arc, gas-flux, plasma, etc.) is carried out on each part that has been cut. The groove edges should not have any traces of cutting (for parts made of low-carbon, manganese and silicon-manganese steels) and traces of marking (punching) applied to the outer surface of the parts after cutting. 6.4.7. Requirements for performing measurement control when preparing parts for assembly are given in table. 3, and when assembling joints for welding - in table. 4. Table 3 Table 4 Controlled parameters Table 5 Weld Measurement Requirements 6.5.5. Measurement control of the geometric dimensions of the welded joint (structural elements of welded seams, the geometric position of the axes or surfaces of welded parts, grooves between the beads and flaking of the seam surface, convexity and concavity of the root of one-sided seams, etc.) should be carried out in the places indicated in the working drawings, ND, PTD or MPC, as well as in places where the admissibility of these indicators raises doubts based on the results of visual inspection. When inspecting butt welded joints of pipes with an outer diameter of up to 89 mm inclusive with the number of similar joints of more than 50 on one product, it is allowed to determine the dimensions of the seam for 10-20% of joints in one or two sections, provided that during visual inspection, which all joints are subjected to , there is no doubt about the deviation of the dimensions (width, height) of the seam from the tolerance. 6.5.6. When measuring control of the deposited anti-corrosion coating, its thickness on cylindrical surfaces is to be carried out at least every 0.5 m in the axial direction and every 60 ° around the circumference for manual surfacing and 90 ° for automatic surfacing. On flat and spherical surfaces, at least one measurement is carried out in each area up to 0.5x0.5 m in size with automatic surfacing. 6.5.7. When inspecting fillet welds of welded joints, the legs of the weld are measured using special templates (Fig. 11). Determination of the dimensions of the height, convexity and concavity of the fillet weld is performed by calculation and only in cases where this requirement is provided for in the design documentation. Measurement of the convexity, concavity and height of the fillet weld is carried out using templates, for example, the V.E. Usherov-Marshak (see Fig. 6). 6.5.8. The measurement of the depth of sinks between the rollers, provided that the heights of the rollers differ from each other, is performed relative to the roller having a lower height. Similarly, the depth of the ridge flakes is determined (at the lower height of two adjacent flakes). 6.5.9. Measurement control of welded joints and weld surfacing (height and width of a welded seam, thickness of surfacing, dimensions of legs of fillet welds, sinking between beads, flakiness of a weld, convexity and concavity of a root weld, the amount of fracture of the axes of the connected cylindrical elements, shape and dimensions of a burr, etc. ) specified in paragraphs. 6.5.5, 6.5.8 and table. 8, should be carried out in the areas of the seam where the permissibility of these indicators is questionable according to the results of visual inspection, if the ND and PDD do not contain other instructions. 6.5.10. The convexity (concavity) of the butt seam is estimated by the maximum height (depth) of the seam surface location from the level of the outer surface of the parts. In the case when the levels of the surfaces of parts of the same standard size (diameter, thickness) differ from each other, measurements should be made relative to the level of the surface of the part, located above the level of the surface of another part (Fig. 12). Rice. nine. Vernier caliper type ШЦ-1 with support: 1 -
calipers; 2
- support Rice. 10. Undercut measuring device: 1
indicator "0-10" with a rotary scale; 2
- support bracket; 3 -
measuring needle Rice. eleven. Special template for weld seam inspection Rice. 12. Measurement of the bulge (concavity) of the butt joint () at different levels external surfaces of parts caused by displacement when assembling a connection for welding In the case when parts with different wall thicknesses are welded and the surface level of one part exceeds the surface level of the second part, the assessment of the convexity (concavity) of the seam surface is performed relative to the line connecting the edges of the seam surface in one section (Fig. 13). Rice. 13. Measuring the convexity (concavity) of a butt weld (
) for different the level of the outer surfaces of parts caused by the difference in wall thicknesses 6.5.11. The convexity (concavity) of the fillet weld is estimated by the maximum height (depth) of the weld surface location from the line connecting the edges of the weld surface in one cross section (Fig. 14). Rice. fourteen. Bulge measurement (
) and concavity (
) the outer surface and heights ( h) fillet weld 6.5.12. The dimensions of the convexity (concavity) of the butt (Fig. 13) and corner (Fig. 14) seams are determined by templates, for example, the design of V.E. Usherov-Marshak or specially designed specialized templates for this purpose. 6.5.13. The convexity (concavity) of the root of the weld is estimated by the maximum height (depth) of the location of the surface of the root of the weld from the level of the location of the inner surfaces of the welded parts. In the case when the levels of the inner surfaces are different, measurements of the convexity (concavity) of the weld root should be carried out according to Fig. fifteen. Rice. fifteen. Measuring convexity () and concavity (
) the root of the seam of the butt one-sided seam 6.5.14. Measurements of individual dimensions of a welded joint using a universal template of the UShS type are shown in Fig. sixteen. Rice. sixteen. Measurements using a UShS template of the dimensions of the weld: but - measuring seam height (#S) and undercut depth ( h ); b- measurement of the seam width ( e); in - measurement of sinks between rollers () 6.5.15. Measurements of scaling and sinking between the beads of the seam, the depth and height of the depressions (bulges) in the weld and the metal are allowed to be determined by the impression taken from the controlled area. For this, plasticine, wax, gypsum and other materials are used. Measurements are carried out using a magnifying glass or microscope after cutting the impression mechanically. 6.5.16. Measurements of the fracture of the axes of cylindrical elements and the angular displacement of the planes of the parts, as well as the asymmetry of the fitting (welded pipe in the corner joint of pipes) should be carried out taking into account paragraphs. 6.6.9 and 6.6.10. 6.6. The procedure for performing visual and measuring control of welded structures (assemblies, elements) 6.6.1. Visual inspection of welded structures (assemblies, elements) provides for checking: deviations in the relative position of the elements of the welded structure; the presence of marking of welded joints; the presence of marking of welded structures (assemblies); absence of surface damage to the material caused by deviations in manufacturing technology, transportation and storage conditions; the absence of unremoved welded elements (technological fasteners, lead-out strips, combs, bosses, etc.). 6.6.2. Measuring control of bent pipe bends provides for checking: deviations from a round shape (ovality) in any section of bent pipes (elbows); wall thickness in the stretched part of the bent section of the pipe (it is recommended to carry out with thickness gauges); radius of the bent pipe section (elbow); the height of the waviness (corrugation) on the inner circumference of the bent pipe (elbow); irregularities (smooth) on the outer contour (in cases established by the normative document); limit deviations of overall dimensions. 6.6.3. Measurement control of tees and extended neck manifolds includes checking: eccentricity of the axis of the neck relative to the axis of the body; radii of transition of the outer and inner surfaces of the neck to the body; the size of the local grooves from the tool on the inner surface of the tee caused by the tool used; reducing the diameter of the body due to metal tightening when upsetting (drawing) the neck; the angle of the cone on the outer surface of the nozzle; local thickening of the neck wall, ovality of the straight sections of the tee body along the outer diameter at the point of the die splice; the circular seam of the adapter ring. 6.6.4. Measurement control of transitions made by rolling (sequential crimping), upsetting at the end and rolling of sheet steel with subsequent welding provides for checking: the sizes of grooves and grooves on the inner surface of the crimped end, which are in the nature of snakes; thickening of the wall on the conical part of the transition; the shape and size of the seam, the absence of unacceptable surface defects. 6.6.5. Measurement control of welded products (parts) of tees, flange connections, sector bends, manifolds, pipe blocks, etc. provides for checking: the dimensions of the misalignments of the axes of cylindrical elements; straightness of the generatrix of the product; deviations of the union (pipe to be welded, branch pipe) from perpendicularity relative to the body (pipe, sheet), into which the union (pipe, branch pipe) is welded; deviations of the axes of the end sections of the welded sector bends; curvature (deflection) of the body (pipe) of welded corner joints of pipes (welding of a pipe, fitting); deviations in dimensions that determine the location of the nozzles in the blocks; deviation of the axis of straight blocks from the design position; deviations of the overall dimensions of welded parts and blocks. 6.6.9. The fracture of the axes of the pipe parts and the straightness of the generatrix are determined in 2-3 sections in the zone of the maximum fracture (deviation of the generatrix from straightness), revealed by visual inspection. Perform the measurement in accordance with the requirements given in clause 6.4.12 and Fig. 3. In the case when measurements according to this method do not provide the required accuracy, measurements should be carried out according to a special method. 6.6.10. The deviation from the perpendicularity of the outer surface (axis) of the union to the body (pipe) is determined in two mutually perpendicular sections (Fig. 18). 6.6.11. Determination of the pipe diameter when measuring with a tape measure is carried out according to the formula where R - circumference measured with a tape measure, mm; t - tape tape thickness, mm. Rice. 18. Measurement of deviation () from perpendicularity the outer surface of the union 6.6.12. Measurements should be carried out in areas where the angular and linear dimensions are in doubt based on the results of visual inspection. Table D1 Table D2 Requirements for the content of the Journal of accounting of works and registration Table 1 Permissible measurement error during measurement control At the moment, due to the fact that there are no approved formulas, in all programs in which cadastral engineers work, two formulas are used ... - one of the "method.recommendations for conducting land surveying" (approved by Roszemkadastrom from 17-02-2003) , looks like - ΔР = 3.5 Mt √Р I want to discuss the use of formula # 1 from the method.recommendations .. ΔР = 3.5 Mt √Р
You know perfectly well that there are cases (and often) when in order, decree, etc. there is one area, but in fact (due to circumstances) it is slightly different, please do not confuse it with 10% and the like when specifying. Always, by default, I used the first formula, and it came as a surprise to me the remark of the local KP - "why do you have the actual area under the root sign?" At first, naturally, I wanted to be indignant, but then I decided to read the theoretical part all the same, I found out - where the legs grow from ... and it seems like the KP is right ... In the source, i.e. Method.recommendations give a completely understandable interpretation of the permissible error. And the main thing is that the documentary area from permissions is used under the root sign ... But it is not entirely logical that the actual area is used in another formula from the instruction. Well, it can't be like that ... I'm certainly not a mathematician, but if you want to get the result of calculations, the formulas may be different, but the source code is not ... So gentlemen and ladies - I know perfectly well, as long as there is no NPA, there can be no consensus, but still! who has this formula in software ??? I do not even stutter about how it is correct ... using the actual or permissive area under the root? I have already asked colleagues working in other software, it turned out that their formula is calculated exactly according to the method recommendations, i.e. based on their permissive area, it means who is in the forest - who is for firewood ... And now I have a small fork - the cadastral waving its finger and threatening "we will not accept", I can not change anything in the program, the developers defend their position .. but I have something a little tight with the argumentation .. Of course, I will try to make a boundary using the second formula, but I'm afraid that the KP, by analogy, will not start demanding the area from the permits ..
Use of terminology
16/32 channels, 16 bit, 2 MHz, USB, EthernetControlled parameter Control type Control requirements
1. Outside diameter ( D), inner diameter ( D )
Measuring Measurement D and D at both ends of the pipe. Measurement D produced when supplying pipes by inner diameter
2.Thickness of sheet, pipe wall ( S )
Also Measurement S at both ends of the pipe in at least two sections. Measurement S sheet in at least two sections (length, width) on each side of the sheet
3. Ovality of the pipe (a) »
Size measurement but at both ends of the pipe
4. Curvature of the pipe (b) »
Measurement of curvature in a section of 1 m in two sections along the length
5. Length of pipe, sheet ( L)
Measuring Measurement of at least 3 pipes (sheets) from a batch
6. Sheet width ( IN)
Also Measurement of at least 3 sheets from a batch
7. Cracks, captivity, flaws, sunsets, shells, bundles Visual Examination of the outer surface with the naked eye; inspection of the inner surface of the pipes with the naked eye (if there is access) and with the help of a periscope, endoscope, etc. It is allowed to cut out control samples with a length of 200 mm in an amount of at least 2 pieces. and their inspection after cutting
Controlled parameter Legend (fig. 8) Figure number Measuring instruments. Measurement requirements
1. Seam width e, e
8, but, in
Vernier caliper or universal template. Measurement - see p. 6.5.5
2. Seam height q, q
8, but, in
Also
3. The bulge of the back of the seam q
8, but, in
Calipers. Measurement according to clause 6.5.5
4. Concavity of the reverse side of the seam q
8, b
Vernier caliper, including a modernized one (Fig. 9). Measurements in 2-3 places in the zone of maximum value
5. Depth of undercut (incomplete filling of the groove) b , b
8, G
Vernier caliper, including a modernized one (Fig. 9). Undercut measuring device (fig. 10)
6. Fillet weld leg TO, TO
8, f
Vernier caliper or template. Measurement according to clause 6.5.5
7. Scaly seam
8, d
Vernier caliper, including a modernized one (Fig. 9). Measurements at least 4 points along the seam length
8. The depth of sinks between the rollers
8, d
Also
9. Dimensions (diameter, length, width) of single discontinuities d, l, b
8, e
Measuring magnifier. Each discontinuity must be measured
Hello forum users! I want to ask everyone about the formula for determining the maximum permissible error in determining the area of the memory. Much has been written on the point error, but very, very little about the area error.
second of "Instruction for land surveying" (approved by Roskomzem on 04/08/1996), it is impossible to write it correctly, but you understand ...
To be honest, to my shame, I have never scrutinized and did not parse these formulas thoroughly, leaving it on the conscience of software developers, i.e. considers the error - the program ... but now, after moving to another city, circumstances forced ...
I wrote to the software developers, asking for comments on this point, and so - their position in short - "under the root should be the actual area, because this follows from 921 orders ...
"The formulas used to calculate the maximum permissible error in determining the area of land plots (parts of land plots) () are indicated in the boundary plan with the values substituted into these formulas and calculation results. "And it seems logical too ....
