How to use the impedance tester

In this article, we will introduce the basic measurement methods of impedance analyzers.

outline

An impedance tester is an instrument used to measure AC resistance or impedance. The basics related to impedance, the measurement of impedance and the use of an impedance tester will be described in detail here.

■ What is the impedance?

What is impedance? Simply put, it is "a quantity that indicates how difficult it is for alternating current to flow."

When an electrical product or motor is connected to an AC power source, current flows through the circuit. The ratio of voltage to current in the circuit at this point is the impedance. In other words, it controls the flow of current in an AC circuit. Impedance is abbreviated as "Z" and has the same unit of "Ω" (ohms) as DC resistance. The higher the impedance, the harder it is for current to pass through.

■ How is impedance measured?

Impedance itself is not visible, so it must be measured using a measuring instrument. Instruments that can measure impedance include impedance testers, LCR testers, and impedance analyzers. In addition, there are several different methods of measurement.

bridge method

This method is used to determine an unknown resistance in a bridge circuit. Requires the use of an ammeter for balancing. Highly accurate (~0.1%) but not suitable for high speed measurements.

I-V measurement

Measure and calculate the voltage across the current-sensing resistance and the unknown impedance, respectively. Measurements can also be made on grounded samples, but the voltmeter will be affected by the size of the impedance.

RF I-V measurement

The measurement principle is basically the same as the I-V measurement method. High-frequency impedance measurements are possible by using a circuit and high-frequency coaxial connector that matches the characteristic impedance of the high-frequency coaxial. Since the measurement band is limited by the transformer of the test head, it is difficult to realize wide bandwidth measurement.

Automatic balanced bridge method

The principle is basically the same as the bridge method. The frequency range is wide, covering 1 mHz to 100 MHz, but it does not include high frequencies. Many LCR testers use this technique.

Since there are advantages and disadvantages to different measurement methods, it is necessary to specify what kind of impedance you want to measure before choosing a method of measuring impedance.

■ How to use the impedance tester

Depending on the measuring instrument, impedance is measured in different ways. For example, HIOKI HIOKI's LCR Tester IM3523 has a wide measurement range and high measurement accuracy.The LCR Tester IM3523 can be used not only for general measurements, but also for continuous and rapid measurements of different measurement items under different measurement conditions (measurement frequency, signal level).

In addition, the LCR tester IM3523 can save up to 60 sets of measurement conditions and 128 compensation values for open/short circuit compensation, line length compensation, and so on. Moreover, saved measurement conditions can be read immediately using the panel save function, thus improving work efficiency. In addition, reading the panel number using the external control port reduces the time required to construct an automated inspection line.

■ Factors contributing to impedance measurement instability

Using different measurement methods, the impedance tester may display different values each time. If the measurement value displayed by the impedance tester is not stable, check the following points.

Correlation factor of the component to be measured

Not only the originally designed resistance and impedance, but also other correlating factors of the component under test may cause the measured value to deviate. Even differences in the length and spacing of the wires connecting the components can lead to changes in the measured values.

Measurement environment

Not only resistance, but the results of impedance measurements can be affected by a variety of conditions such as the temperature of the capacitor or inductor, the capacitance of the probe, and stray capacitance.

It is therefore necessary to take precautions such as keeping the measurement environment constant and averaging several measurements rather than making a decision based on just one measurement.

DC bias voltage

DC bias is a DC bias is a very small voltage generated by a measuring instrument or circuit. For example, a difference in the material of the probe and the material of the wiring can cause a thermal electromotive force to be generated, resulting in a DC bias.

▪ Summary

Impedance is the resistance of AC and requires a specialized measuring instrument to measure. There are various measurement methods, so it is important to select the appropriate one based on its advantages and disadvantages and the purpose of the measurement.

Impedance measurements are very sensitive and tend to be biased by factors such as frequency, the measurement environment, DC bias, and so on. When measuring, it is necessary to take precautions such as making multiple measurements and averaging them.