Measuring instruments

To measure the parameters of on-board electricians, so-called universal measuring instruments are sold in the distribution network. They combine in one device a voltmeter for measuring voltages, an ammeter for measuring current strength and an ohmmeter for measuring resistances. Rotary or pushbutton switch selects the desired measuring range (V, A, W). The proposed instruments differ mainly in their measurement ranges and accuracy. The measurement range indicates what value the voltage or resistance must have in order to be measured by this instrument. The measurement accuracy is determined, first of all, by the manufacturing costs, which, of course, are reflected in the price. The higher the accuracy, the higher the selling price.

For car enthusiasts, there are multi-purpose measuring instruments that are designed specifically for measurements in a car. One such device can measure the crankshaft speed, the angle of the closed state of the breaker contacts and, in addition, voltages up to 20 volts. The measurement range of such a resistance device is limited, as a rule, to the region of kiloohms, that is, 1 - 1000 kOhm. If the device allows the measurement of current, then only in the starter circuit.

In addition, measuring instruments are available for testing electrical and electronic parts. These devices do not have the ability to measure the speed of the crankshaft and the angle of the closed state of the breaker contacts.



The great advantage of these instruments is that they allow extensive measurements from small resistances in ohms (Ohm) up to very high resistances in megohms (MOhm). Voltage (in volts) can be measured with an accuracy of three decimal places, which is primarily required for electronic parts.

When it is only necessary to check whether there is voltage at all in the circuit, a simple test lamp -A- is suitable for this. First of all, it is only suitable for monitoring electrical circuits that do not contain any electronic parts.

This is due to the fact that electronic components are extremely sensitive to high currents and, under certain circumstances, can fail even when a test lamp is connected. To monitor the electronic components of vehicles, such as, for example, the transistorized ignition system or the electronic control unit for the injection system, a voltage indicator with a high internal resistance -B- is required. It works like a warning lamp, but does not cause damage to the electronic components.