Measure very low resistances

Measure resistance
very small

There is a special case of a resistance measurement where the value of the component to be measured is very small and the direct measurement with a multimeter / DMM is not practical.

The cases mentioned include:
- Measuring the resistance of a track on a printed circuit
- Measuring the resistance of a coil (the resistance that has all the turns of a coil or inductor )
- Etc.

In this case, an indirect measurement is performed with the aid of a voltage
source, an ammeter and a voltmeter.



Connect the power supply and a current limiting resistor as shown in the chart below. Thus a current will (relatively large) by the component to be measured (printed circuit track, winding, etc.).

To achieve this you can use a voltage source of 10 volts and a limiting resistor 20 ohms (ohms) 10 watts (watts).
In series with the circuit has an ammeter, where will the current flowing around the circuit.

Measure the drop in voltage at the ends of the component with the help of the voltmeter and with the help of Ohm's law gives the strength of the component (Rx). Rx = Vx / I

Example:
Using the graph above. The value of the current measured with the ammeter is 450 mA and the voltage measured at the component is 10 mV, then the strength of the component will be:

Rx = 10mV / 450mA = 0.0222 ohms

Note: this measurement obtained with a very low resistance value is required, ensure that the ends or terminals to be used in the voltmeter are of a resistance very low (almost nil) (make a prior review).