Self - verification questions

1. What does the term “standardization of MI metrological characteristics” mean? What is it used for?

2. What the most important metrological characteristics of MI are standardized?

3. What are “the limit of a permissible error” and ”the accuracy class” of MI?

4. Does the high accuracy classes MI use guarantee the small measurement errors? How can your conclusions be proved with the numerical examples?

5. In what way and for which MI the accuracy classes on the absolute error are standardized? What are their designations?

6. In what way and for what MI the accuracy classes are standardized on the relative error? What are their designations?

7. How are the accuracy classes of the digital measurement instruments standardized and designated?

8. How can the permissible absolute error of a deflectional instrument be calculated from its known accuracy class and the fiducial value?

9. According to what rules a measurement range and an accuracy class of a deflectional instrument for measurement of the quantity given with the admissible deviation are selected?

10. According to what rules a measurement range and an accuracy class of a deflectional reference instrument for verification of a working deflectional instrument by the juxtaposition method are selected?

SYSTEMATIC ERRORS.

A division of the errors into random and systematic is very conventional. It is stipulated first of all by knowledge of the causes of the errors arising and regularities, connecting the errors with these causes. If this knowledge is available, the errors become well determined, foreseeable and forecasted. In this case the errors that we cannot understand at once, in appearance of which we can see no regularities, i.e. random errors, by a further deep research of the measurements results and everything connected with them, may be transferred to the systematic ones.

This rather complicated process demands a deep knowledge, experience, and comprehension of all the circumstances that accompany a measurement experiment. To make the process of the systematic errors detection easier, let us classify them in detail.

The methodical errors are typically systematic. Having analyzed the measurement method, phenomena and formulas that are laid in its foundation, it is possible to reveal the sumptions and simplifications, causing the systematic errors appearance.

For example, at measurement of a temperature by using a thermocouple, it is necessary to remember that the electromotive force, depends not only on the temperature being measured (unfortunately on non strictly linear characteristic), but also on the thermocouple cold-junctions temperature. Ignoring to these factors results in the systematic errors arising.

The instrumental errors may also have the substantial systematic components. For example, inaccuracies in the scale gauging, adjusting of multiplier resistors, voltage dividers, etc. The systematic instrumental error also arise due to an incorrect location of an instrument on inclined plane instead of horizontal one. The electromagnetic fields of the closely-spaced instruments can interact, that results in a distortion of the readings by the systematic errors.

The complementary errors, appearing because of the MI usage in the conditions discrepant of the normal ones, prescribed in the documentation, also may be referred to the systematic errors.

The dynamic errors of MI that are displayed as a MI indications lag when measuring the fast varying quantities, also may be referred to systematic errors.

The error from interaction that arise as a result of the MI influe –

nce on the object is typically systematic, too.

Therefore, it is always necessary to analyse how a regime of object action will be changed after a certain MI connection to it and to take all due measures to diminish this influence.

The personal error, that is specified by the personal peculiarities of an operator may possess by a systematic component as well. It can be detected by comparing of the one-type observations results held by the different operators.In general, for the systematic errors revealing it is very useful to learn and analyze different models of object and measurement experiment, to plot graphs, etc.