rus
Issue #2/2018
S.Stepanov, S.Tarasov, A.Petrov, S.Stepanov
Determination of absolute error of M-050-03 electronic level
Determination of absolute error of M-050-03 electronic level
A calibration technique has been developed to determine the actual error of electronic levels. It is determined that the M-050-03 electronic level can be used in the local scheme as standard of the 1st category.
The Mikro engineering and metrology center produces the M-050-03 electronic level, which corresponds to the levels of the 2nd category according to the "State verification scheme for measuring devices for deviations from straightness and flatness". This level can not be verified with granite testing plates of grades 0 and 00, as well as rulers with a wide working surface of hard rock of accuracy class 0 for which the flatness tolerance does not exceed 2.5 μm, since its minimum error is 2 μm/m. This characteristic of the level is confirmed by its annual verification.
The actual level error can be determined by calibrating it. All the world's leading manufacturers of linear angle measuring instruments supply their instruments with a calibration certificate, indicating their actual error and calculating the uncertainty of measurements during use.
In 2014, GOST R 8.879-2014 "Calibration techniques of measuring instruments" was adopted, which was enacted from 09.01.2015, and in 2017, VNIIMS developed guidelines for the implementation of GOST R 8.879-2014 "State system for ensuring the uniformity of measurements. Calibration techniques of measuring instruments. General requirements to the contents and statement", so the calibration and determination of the absolute error of the level with the calculation of the measurement uncertainty became even more urgent.
The developed calibration procedure extends to the M-050 electronic levels of the modifications M-050-01/02/03 (hereinafter referred to as "levels") and establishes the procedure for calibrating in order to confirm their compliance with the working standard of the 1st category in accordance with GOST 8.420-2002 "State verification schedule for means of measuring straightness and flatness deviation".
All preparatory operations and requirements for calibration tools are described in the calibration procedure. The main indicators in the calibration, on the basis of which it can be concluded that the level can be used to verify the plates and rulers of classes 0 and 00, that is, to recognize it as the appropriate standard of the 1st category, is the limit of the absolute error δ for forward and reverse traces, as well as the value of uncertainty.
The measuring range of the M-050 level is ±1500 μm/m. It is not possible to provide an absolute error of 1.5 μm/m over the entire measurement range, as required by the calibration scheme, so we confine ourselves to a range of ±100 μm/m, which is sufficient to provide a measurement of the flatness deviations of the mentioned plates and rulers.
DETERMINATION OF ABSOLUTE ERROR LIMIT OF LEVEL FOR FORWARD AND REVERSE TRACES
During the calibration we use the examiner of the 1st category, which is set to the middle position in accordance with the operational documentation for it. The calibrated level is set on the examiner's table in the longitudinal direction to the longitudinal and transverse stops. With the help of the level, we set the examiner's table in the horizon and reset the level and examiner's readings. Then we perform the following steps:
• turn the examiner's table 5 μm/m from the zero position in the positive direction and take the reading from the electronic unit БИН 2И of the level;
• before the testimony of 20 μm/m, take the reading from the electronic unit every 5 μm/m;
• further – up to the testimony of 60 μm/m – every 10 μm/m;
• further – up to the testimony of 100 μm/m – every 20 μm/m;
• we pass the reading of 100 μm/m on approximately 20 μm/m and return to the mark of 100 μm/m on the other side, after which we take the reading on the БИН 2И unit. Then we pass to zero from the reverse side in the same points of the range as in the forward trace;
• repeat the above in the negative range to –100 μm/m.
The level error in the control points of the range is the difference between the readings of level and examiner. The determination of the level error at the reference points of the range in forward and reverse traces is performed five times with the condition of repeatability, after which the average value should be calculated. As the limit of the absolute error δ, we take the algebraic difference between the largest and smallest mean errors at control points.
The limit of absolute error δ should not exceed 1.5 μm/m.
Results of the calibration:
• absolute error of the level A – δ = 0.63 μm/m;
• absolute error of the level B – δ = 0.97 μm/m.
ESTIMATION OF UNCERTAINTIES
The total standard uncertainty of measurement of the absolute error of the level is calculated by the formula:
,
where: is standard uncertainty (type A) of the mean absolute error, μm/m,
;
is arithmetic mean of the results of measurements of the i-th input value;
is standard uncertainty (type B) from level discreteness, μm/m;
is standard uncertainty (type B) from examiner discreteness, μm/m;
is standard uncertainty (type B) of the limit of the admitted absolute error of the examiner, μm/m.
The expanded uncertainty of the absolute error of the level is calculated for each control point of its calibration characteristic by the formula U = uс ∙ k with a probability of 0.95.
For X–max = 0.46, the extended uncertainty of the level A X–min = 0.43.
For X–max = 0.43, the extended uncertainty of the level B X–min = 0.44.
CONCLUSION
Level calibration by the developed technique allows to determine the actual value of the error of electronic levels, in contrast to verification, which confirms the technical characteristics.
The calibration results showed that these M-050-03 electronic levels can be used in the local scheme as standards of the 1st category. ■
The actual level error can be determined by calibrating it. All the world's leading manufacturers of linear angle measuring instruments supply their instruments with a calibration certificate, indicating their actual error and calculating the uncertainty of measurements during use.
In 2014, GOST R 8.879-2014 "Calibration techniques of measuring instruments" was adopted, which was enacted from 09.01.2015, and in 2017, VNIIMS developed guidelines for the implementation of GOST R 8.879-2014 "State system for ensuring the uniformity of measurements. Calibration techniques of measuring instruments. General requirements to the contents and statement", so the calibration and determination of the absolute error of the level with the calculation of the measurement uncertainty became even more urgent.
The developed calibration procedure extends to the M-050 electronic levels of the modifications M-050-01/02/03 (hereinafter referred to as "levels") and establishes the procedure for calibrating in order to confirm their compliance with the working standard of the 1st category in accordance with GOST 8.420-2002 "State verification schedule for means of measuring straightness and flatness deviation".
All preparatory operations and requirements for calibration tools are described in the calibration procedure. The main indicators in the calibration, on the basis of which it can be concluded that the level can be used to verify the plates and rulers of classes 0 and 00, that is, to recognize it as the appropriate standard of the 1st category, is the limit of the absolute error δ for forward and reverse traces, as well as the value of uncertainty.
The measuring range of the M-050 level is ±1500 μm/m. It is not possible to provide an absolute error of 1.5 μm/m over the entire measurement range, as required by the calibration scheme, so we confine ourselves to a range of ±100 μm/m, which is sufficient to provide a measurement of the flatness deviations of the mentioned plates and rulers.
DETERMINATION OF ABSOLUTE ERROR LIMIT OF LEVEL FOR FORWARD AND REVERSE TRACES
During the calibration we use the examiner of the 1st category, which is set to the middle position in accordance with the operational documentation for it. The calibrated level is set on the examiner's table in the longitudinal direction to the longitudinal and transverse stops. With the help of the level, we set the examiner's table in the horizon and reset the level and examiner's readings. Then we perform the following steps:
• turn the examiner's table 5 μm/m from the zero position in the positive direction and take the reading from the electronic unit БИН 2И of the level;
• before the testimony of 20 μm/m, take the reading from the electronic unit every 5 μm/m;
• further – up to the testimony of 60 μm/m – every 10 μm/m;
• further – up to the testimony of 100 μm/m – every 20 μm/m;
• we pass the reading of 100 μm/m on approximately 20 μm/m and return to the mark of 100 μm/m on the other side, after which we take the reading on the БИН 2И unit. Then we pass to zero from the reverse side in the same points of the range as in the forward trace;
• repeat the above in the negative range to –100 μm/m.
The level error in the control points of the range is the difference between the readings of level and examiner. The determination of the level error at the reference points of the range in forward and reverse traces is performed five times with the condition of repeatability, after which the average value should be calculated. As the limit of the absolute error δ, we take the algebraic difference between the largest and smallest mean errors at control points.
The limit of absolute error δ should not exceed 1.5 μm/m.
Results of the calibration:
• absolute error of the level A – δ = 0.63 μm/m;
• absolute error of the level B – δ = 0.97 μm/m.
ESTIMATION OF UNCERTAINTIES
The total standard uncertainty of measurement of the absolute error of the level is calculated by the formula:
,
where: is standard uncertainty (type A) of the mean absolute error, μm/m,
;
is arithmetic mean of the results of measurements of the i-th input value;
is standard uncertainty (type B) from level discreteness, μm/m;
is standard uncertainty (type B) from examiner discreteness, μm/m;
is standard uncertainty (type B) of the limit of the admitted absolute error of the examiner, μm/m.
The expanded uncertainty of the absolute error of the level is calculated for each control point of its calibration characteristic by the formula U = uс ∙ k with a probability of 0.95.
For X–max = 0.46, the extended uncertainty of the level A X–min = 0.43.
For X–max = 0.43, the extended uncertainty of the level B X–min = 0.44.
CONCLUSION
Level calibration by the developed technique allows to determine the actual value of the error of electronic levels, in contrast to verification, which confirms the technical characteristics.
The calibration results showed that these M-050-03 electronic levels can be used in the local scheme as standards of the 1st category. ■
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