What is an impedance tester?

The text will introduce the basics of impedance and the key points of measurement.

Impedance is the resistance of an AC circuit and is invisible. Therefore, it must be measured using a specialized measuring instrument such as an impedance tester. If you are someone who has never touched an impedance tester before, you may be more concerned about how it is used and what to look for when using it.

Therefore, this paper will present the basics of impedance, the use of an impedance tester, and the precautions to be taken when making measurements in an easy-to-understand manner.

▪ What is impedance?

Some of you may not know what impedance is. Impedance is a quantity that indicates how difficult it is for an alternating current to flow. Impedance is often expressed as Z in Ω (ohms).

 Therefore, when the voltage across a conductor is certain, the higher the resistance, the smaller the current through it; conversely, the lower the resistance, the higher the current through it. Impedance is of great importance in the field of electrical circuits.

▪ Is there a difference between an impedance and a resistance in a DC circuit?

Impedance is also a type of resistance, and the unit is expressed in Ω like DC resistance. However, DC resistance and impedance are not exactly the same. While they are the same in the grand scheme of things, AC impedance is more complex.

In a DC circuit, a resistor (R) acts as a barrier to current flow. In AC circuits, in addition to the resistance (R), the coil (inductance L) and capacitance (C) also act to block the passage of current.

■ Measuring impedance requires the use of an impedance tester

Impedance is not visible, so to determine impedance, specialized measuring instruments must be used. Instruments that can measure impedance include impedance testers, LCR testers, and impedance analyzers.

There are many ways to measure impedance, and each of these methods has advantages and disadvantages. Therefore, it is important to select an instrument for measuring impedance based on the type of measurement you want to make and the accuracy you want to obtain.

The following table summarizes the methods for measuring impedance. This ensures that you are aware of the types of measurements that can be performed corresponding to each method.

■ Points to note when measuring with an impedance tester

Impedance measurements are very sensitive and in many cases measurements tend to be unstable. The main factors include the following.

・Deviations due to the measured component.

Due to the effect of individual differences in the components to be measured, in some cases the measured values may not be exactly the same even under the same conditions.

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.

Deviations due to operating conditions

When measuring capacitance and inductor temperature, probe capacitance, and high-impedance components, changes in the measurement environment such as the effect of external electromagnetic induction noise can affect the measured values. In addition, they are affected by DC bias voltages generated by the measurement circuits and measurement instruments.

As a result, impedance measurements are susceptible to bias and it is necessary to take precautions such as making multiple measurements and averaging them.

▪ Summary

There are various types of impedance testers, each with its own different measurement methods and frequency ranges. Please clarify the type of measurement you want to make and select the impedance tester that best suits your needs. In addition, impedance measurements are susceptible to deviations due to various factors, so it is necessary to take precautions such as repeated testing.