13.1.2. Measuring devices

For measurement of electric parameters in an onboard chain on sale there are so-called combined measuring devices which in one device unite the voltmeter for voltage measurement, the ampermeter for measurement of current and an ohmmeter for measurement of resistance.

The measuring devices which are available on sale differ among themselves mainly with the range and accuracy of measurements. Is established by the range of measurement in what area there have to be registered tension and resistance.

For motorists there are combined measuring devices which are specially intended for holding examinations in the car. By means of such device it is possible to measure the frequency of rotation of a shaft in the car, a corner of the closed condition of contacts of the breaker of system of ignition and tension up to 20 Century.

At measurement of resistance the device is, as a rule, limited to range in kilohms, In addition to it measuring devices are used to check of electric and electronic elements of a design. They allow to take broad measurement from small resistance in Ohms up to megaomny range. It is very precisely possible to measure tension (V) that first of all is required for check of electronic elements of a design.

If it is only necessary to check whether tension (V) moves in general, then the simple control bulb for this purpose approaches (And). However, it is valid only for those electric chains in which there are no electronic details. Nevertheless electronic details extremely sensitively react to too high currents. Under certain circumstances they can fail even at connection of a control bulb.


Prevention

When checking electronic details (transistors, diodes and the operating knots) it is necessary to use the high-resistance indicator of tension (In). It works as well as a control bulb, however without damage of electronic elements of a design, and is suitable for carrying out all control operations.