8: QUALITY EVALUATION BY IMPORTANT AND GENERAL INDICATORS

Lecture questions:

1. The most important quality indicator

2. Application specificity and calculation of a single or determinative indicator

3. Generalized indicator of the group of properties

4. Functional dependence in the calculation of the generalized index

1. The most important quality indicator

Sometimes the quality of technical products is evaluated on a single, but the main, defining indicator characterizing its usefulness. The determining factor is the most important property indicator for which a preliminary decision on product quality is taken.

According to the indicators of the main, defining properties, it is possible to preliminarily, but not always, determine which product samples are analogous to the one being assessed, and which sample should be considered as probably basic. However, one, even the defining, indicator gives one-sided, limited

characteristic of products, usually with a large number of properties that make up the quality. Therefore, for almost any product, especially for complex and multi-functional, it is necessary to make a quality assessment for most or all of its useful properties.

2. Application specificity and calculation of a single or determinative indicator

For example, the quality of automobile tires is estimated mainly by their mileage in kilometers to a certain wear, the quality of gasoline

- octane, concrete quality

- by cubic strength with one-sided compression, the quality of coke - by its calorific value, the quality of technological equipment - by productivity, etc.

At the same time, the determined level of quality, its numerical indicator, is the ratio of the magnitude of the main or determining (most important) indicator characterizing the object being evaluated to the corresponding base value, i.e.

Where

Yk is the level of a determining, (main, most important) production indicator taken as a quality indicator;

Pots is the value of the estimated (main, determining) indicator of the unit of product being valued;

Pbaz - the basic value of the same main (determining) indicator.

3. Generalized indicator of the group of properties

A generalized indicator is an indicator that is a function of several (group) individual indicators of the properties of an object.

In many cases, several indicators of properties are interdependent, i.e. have a functional relationship. If it is possible to establish or know this dependence of a certain generalized indicator on several of its initial single indicators of properties, then the quality of an object is sometimes evaluated by

such a generalized index Q = f (Pi), as

4. Functional dependence in the calculation of the generalized index

For example, the main indicator of the quality of the drilling rig, characterized by the length of penetration ( L ) for the service life in meters:

Where

Tср - service life, h;

Tо - time to failure, h;

TV- average downtime per failure, h;

Kprof is a coefficient characterizing the proportion of time spent on prophylaxis for one hour of plant operation;

v - average drilling rate, m / h.

The quality level is found as

Where

Yk - quality level;

Lots - estimated value of the indicator;

L base is the base value of the indicator.

For example, the main indicator of the quality of a bus, characterized by its annual productivity (Wп) in man-km:

Where

Tn - the average duration of the bus in the dress, h;

ve- bus operating speed, km / h;

rn- nominal capacity of the bus, pers .;

- utilization capacity of the bus;

- utilization rate of the bus run;

- bus utilization rate.

In this case, the quality level of the bus is calculated by the formula:

Where

Wp.oc - annual performance of the estimated value of the indicator;

W.baz - annual performance of the base value of the indicator;

Thus, for the application of this method it is necessary to know the functional relationship between the indicators characterizing the quality of products.