How do I measure resistance?

Wondering about resistance measurement methods! In this article, we will introduce basic resistance measurement methods and precautions.

Resistors are very important in electronic device circuits. If the resistance is not appropriate, it can lead to malfunctions and other problems. However, electricity is not visible. To find out if the resistance in a circuit is appropriate, you need to use a specialized measuring instrument.

To measure resistance, you need to use a measuring instrument, but how should you do it? This section details how to measure resistance using a measuring instrument and a multimeter.

■ How to measure resistance

You can use either an analog multimeter or a digital multimeter to measure resistance. Whichever multimeter you use, you can measure not only resistance, but also current and voltage. Just one multimeter can be used for a variety of applications.

However, resistance measurements are not measuring the resistance value within the circuit itself. The resistance value is calculated from the current and voltage in the circuit. When a current is applied to a DUT, a voltage (voltage drop) is generated in the circuit relative to the DUT (resistance). The resistance value can be calculated from the current and voltage using Ohm's law.

Therefore, even if you do not know the resistance value in a circuit, you can calculate the resistance value as long as you have current and voltage measurements. Use an analog multimeter or a digital multimeter to calculate the resistance value using Ohm's law based on the principle of resistance measurement.

■ Measurement of resistance using an analog tester

When using an analog multimeter to measure resistance, turn off the power to the circuit under test. Insert the red test lead into the + input terminal labeled with the resistance symbol and the black test lead into the - input terminal labeled COM.

Turn the switch to resistance and set the range button to the estimated range of the DUT.

Figure 1	Figure 2

Short the red and black test wires, rotate the "Ω" zero potentiometer, so that the pointer points to 0 Ω and then measure. Will be red, black two test line respectively contact resistance to measure the two ends, and then read the indicated value on the meter.

Figure 3	Figure 4

In resistance mode, applying voltage to the test line may cause the measuring instrument to malfunction. In addition, if zeroing is not possible, this may be a result of the analog multimeter's battery being depleted. In this case, check the battery voltage.

Resistance Measurement Circuit for Analog Testers

(Zeroing is necessary when measuring resistance values. (Mechanical zeroing, electrical zeroing) Isolation is very important because any situation with voltage is dangerous.)

■ Measurement of resistance using a digital multimeter

Measuring resistance with a digital multimeter is essentially the same as measuring resistance with an analog multimeter and is very simple. The basic usage is roughly the same, the only difference being that an analog multimeter uses a pointer on a scale to display the measurement, while a digital multimeter displays the measurement on a digital display. However, digital multimeters have two methods of measurement.

・2 terminal measurement method

4-terminal measurement method

The resistance measurement method of a digital multimeter basically uses the 2-terminal measurement method. This method is to measure the resistance value through a voltmeter after flowing a certain current. The same is true for analog multimeters. However, the 2-terminal method has the disadvantage that it does not eliminate the effect of the contact resistance between the test probe and the object under test.

2 Terminal Measurement Method

To minimize this effect, the test probe needs to be shorted and zeroed before measurement.

However, even this cannot be completely removed (error). This led to the four-terminal measurement method, which is performed by using four test leads, in which case the ammeter circuit and voltmeter circuit are independent.

4 Terminal Measurement Method

Many different resistances such as the internal resistance of wires, relays, connectors and batteries need to be measured, so you need a suitable measuring instrument. When purchasing a measuring instrument, select one that meets your needs.

■ Reasons for errors in resistance measurements

It is not only the wiring resistance of the test leads that affects the resistance measurement results. The main influencing factors are also the following.

electric potential

thermal noise

leakage current (of liquid or gas)

absorbs

Friction noise

External Noise

Temperature, humidity, wind.

In order to minimize the effects of temperature and other factors, the resistance meter also has a temperature compensation function. The function of reading the difference between the temperature value of the temperature sensor connected to the resistance meter and the standard temperature, compensating for the measured resistance value, and displaying it is the temperature compensation function of the resistance meter. If the measured value of the resistance is unstable, please understand the reason that affects the measured value before taking corresponding measures.

Rt = Rt0 × { 1 + αt0 × (t - t0) }

Rt: Actually tested resistance [Ω]

Rt0: Compensated resistance [Ω]

t0: Reference temperature [°C]

t: Current ambient temperature [°C]

at0: Temperature coefficient at t0

By using a temperature-compensated resistance meter.

You can automatically capture the temperature-converted resistance value.

(Temperature-compensated resistance meter can be used to automatically read resistance values for temperature changes)

■ 4-Terminal Resistance Meter for More Accurate Low Resistance Measurements

Analog and digital multimeters do not measure the resistance itself, but rather use current and voltage to calculate the resistance value according to Ohm's Law. The usage of both instruments is essentially the same. Digital multimeters can also provide more accurate measurements using the 4-terminal measurement method.

However, resistance values can be affected by many external factors. If the measured value is unstable, an attempt should be made to identify the cause and resolve it.