What is the ideal resistance

Resistance measurement / measure resistance

There are several methods of finding a resistance value. A distinction is made between indirect and direct resistance measurement. The indirect resistance measurement is a measurement with a subsequent calculation. Direct resistance measurement is the usual measurement method in a measuring device, in which the resistance value can be read off or is displayed.
The value of the ohmic resistance is best determined with a digital multimeter (multimeter) in order to avoid reading errors and inaccuracies.

Indirect resistance measurement

In the case of indirect resistance measurement, the voltage U applied to the resistor and the current flowing through the resistor must be measured at the same time.

The resistance value can be calculated from both measurement results with the aid of Ohm's law.

Direct resistance measurement

With the direct resistance measurement, it is not the resistance, but the current through a series circuit of the unknown resistance R.X and a known series resistor RV. measured. In order for a current to flow, a voltage source must be connected to the series circuit consisting of an ammeter, known and unknown resistance.
Direct resistance measurement is used in measuring devices. Instead of current values, resistance values ​​are entered on the scale (analog measuring device).

Occasionally you come across measuring mechanisms with a scale where the greatest resistance value (infinite ohms) can be read on the left and the smallest resistance value (0 ohms) on the right. So exactly the other way around, as one is used to with current and voltage. This is because a current is actually measured and the largest current flows with the smallest resistance and the smallest current flows with the largest resistance.
The internal wiring of the measuring range switch of analog measuring devices usually ensures that the polarity of the measuring inputs is reversed and the scale for resistance values ​​is labeled in the usual way from left to right from the smallest to the largest value. But that is not always the case.

Before measuring the resistance, please note the following:

In a switched-on module, you can measure voltages, perhaps also currents, but never resistances. Let alone check other components or conductor tracks. Components must always be unsoldered. In the case of conductor tracks, at least the power supply must be interrupted.
When measuring resistance, the meter applies a small voltage to the resistor. If other components are connected in series or in parallel, the measurement result will be falsified because the current flows in different ways. In addition, the additional voltage source can be destroyed.

  1. The component to be measured must not be connected to a voltage source during the measurement because the measuring device determines the resistance value via voltage or current.
  2. The component to be measured must be unsoldered from a circuit at least on one side. Otherwise components lying parallel will influence the measurement result.
  3. The correct measuring range must be set.
  4. The measuring range must then be set so that the pointer deflection can be read in the last third (with an analog measuring device).

Overview: measuring electrical quantities

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