Measuring instruments (VW Passat B3)

To measure the parameters of on-board electrics, the retail network sells so-called universal measuring devices. They combine in one device a voltmeter for measuring voltage, an ammeter for measuring current, and an ohmmeter for measuring resistance. The desired measurement range (V, A, W) is selected using a rotary or push-button switch. The offered devices differ mainly in the ranges and accuracy of measurements. The measurement range indicates what value the voltage or resistance must have so that it can be measured by a given device. The accuracy of measurements is determined, first of all, by the cost of production, which, of course, is reflected in the price. The higher the accuracy, the higher the selling price.

For car enthusiasts, there are multi-purpose measuring devices 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 range of resistance measurements by such a device is usually limited to the kilo-ohm region, i.e. 1 - 1000 kOhm. If the device allows measuring current, then only in the starter circuit.

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



The great advantage of these devices is that they allow extensive measurements from small resistances in ohms (Ohm) to very large resistances in megaohms (Mohm). Voltages (in volts) can be measured with an accuracy of three decimal places, which is especially required for electronic components.



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

This is due to the fact that electronic components are extremely sensitive to high currents and under certain circumstances may fail already when the control lamp is connected. To check electronic components of cars, such as, for example, the transistor ignition system or the electronic control unit of the injection system, a voltage indicator with a high internal resistance "V" is required. It works as a control lamp, but does not cause damage to electronic components.

The original article is posted on the website VWmanual.ru