1. 7. Indicators of metrological reliability of measuring instruments. Methods of assessment, regulation and control.

The technique uses a large number of indicators of reliability, which are listed in the Standard GOST 27.002-89 "Reliability in the art. The terms and definitions." Consider the major ones that have found application in the theory of metrological reliability. Knowledge of metrological reliability indexes allows the user to make optimum use of the SI, plan repair power stations, the size of the reserve fund of instruments reasonably assign calibration interval and competently carry out maintenance activities SI.

The metrological reliability, which is characterized by similar, but a failure to understand the output error of the analysis of range. This indicator is related to the probability of occurrence of errors of analysis exceeds the limit permissible error.

Under the metrological reliability of measuring understand their properties are maintained at a predetermined level, the indicators, primarily the accuracy within the required time.

Reliability and metrological reliability is determined primarily by the trouble-free, which is a property of an object continuously keep working for some time or certain performance period.

The required level of metrological reliability depends on the application of measurement and is selected from the conditions necessary to ensure the effectiveness of technical devices serviced.

After verification of the metrological reliability of measuring instruments is increasing. The more frequently performed calibration, the higher average level of reliability in operation devices.

In practical calculations metrological reliability indexes is possible to confine the first few terms of an infinite sum in (1.111 6), (1.112), as described by its number rather quickly converge.

The proposed method allows for the preservation of metrological reliability of IMS, provide test methods improve the accuracy of measurement methods or model measures to improve its performance and makes it possible to work in a dynamic mode.

1. 8. Principles of selection accuracy characteristics of measuring instruments used in the quality control of products.

Quality measurement depends on the correct choice of measurement. This takes into account a number of factors:

measured physical quantity;

measurement method implemented in the measuring medium;

SI range and accuracy;

measurement conditions;

permissible error of measurement;

the cost of measuring instruments;

ease of use;

Resources of measuring instruments;

losses due to measurement errors (marriage types I and II).

The main characteristics of measuring instruments are their error. They are considered in the first place.

 Three basic principles of choice of measurement accuracy:

 Economic Approach - allows for almost all indicators. It should be borne in mind:

improving the accuracy of measurements will help fine tune the production process;

more accurate measurements can reduce the tolerance of the product;

improving the accuracy of measurement results in a decrease in the proportion of undetected and false marriage.

With increasing losses increase the measurement error, while the cost of the measurement are reduced.

 The economically optimal measurement accuracy process parameter corresponds to the minimum amount of losses due to measurement error and measurement of costs, including costs for the metrological service of measuring instruments. Optimum accuracy assessment corresponds to the mean-square (RMS) error.

 The dependence of the losses from the measurement error and the dependence of the cost of the measurement determined in practice exactly what causes uncertainty corresponding characteristics optimal measurement error.

9. Procedure for selection of measuring instruments. Basic requirements A great variety of objects of measurement results in a wide variety of measurement and control instruments and appliances, as well as methods and techniques of measurement. However, depending on the purpose of the individual machine parts, measurements must be made with different accuracy. In one case, it suffices to use conventional scale ruler, and the other - to use an accurate device enabling to make the measurement with an accuracy of ± 0.01 mm in magnitude.

Let's say you want to measure the diameter of the piston. It can be measured with calipers and a scale ruler, caliper and micrometer. In the first case, the accuracy of measurement corresponds to the value of -0.5 mm in the second - from 0.1 to 0.05 mm, and the third - 0.01 mm.

Normal conditions perform linear and angular measurements established GOST 8.050-73. Errors made while measuring the linear dimensions of 1 to 500 mm, depending on tolerance and nominal sizes of products regulated by GOST 8.051-73. Maximum permissible error of measurement takes into account the effect of the error measuring means, setting up, thermal strains, the method of measurement, and so on. D. The result of measurement error not exceeding permissible, mistaken for the actual value.

The main factors influencing the choice of measuring instruments, - the size and kvalitet (class) of the measured product, permissible error measuring conditions and method of use of measuring instruments.

Sliding measuring tool with a linear vernier. Caliper - multidimensional sliding tool vernier * for measuring internal and external dimensions, diameters, depths and heights details. Designs produced calipers allow the countdown sizes up to 0.1 and 0.05 mm. This high accuracy is achieved by using a special device to count - linear vernier.