Detailed explanation of high resistance resistance measurement method

In electronic circuit design and testing,resistanceAs a basic passive component, accurate measurement of its resistance is crucial. Especially high-resistance resistors (usually referring to resistors with a resistance above the megohm level), due to their extremely high resistance, are difficult to measure, and ordinary multimeters often cannot measure them accurately. Therefore, it is particularly important for engineers and technicians to master scientific and effective high-resistance resistance measurement methods. This article will systematically introduce the measurement principles and practical methods of high-resistance resistors to help readers solve measurement problems in practical work.

1. Definition of high resistance resistors and difficulties in measuring them

High-resistance resistors usually refer to resistors with a resistance above 1MΩ (megaohms). This type of resistor is widely used in high impedance circuits, isolation circuits and precision instruments. The main difficulties in measuring high-resistance resistors are: the measurement current is extremely small and is susceptible to environmental interference; the input impedance requirements of the instrument are high; the leakage current of the connecting wires and test fixtures has a large impact, resulting in measurement errors.

2. Use a megger (megohmmeter) to measure

A megohmmeter is an instrument specially used to measure high-resistance resistance, usually with a high-voltage power supply (such as 250V, 500V or even 1000V). It calculates the resistance value by applying high voltage and measuring the leakage current. When using a megger to measure, attention should be paid to firm wiring to avoid leakage paths, and the instrument should be calibrated before measurement. Megger is suitable for measuring insulation resistance and high resistance resistance with high accuracy.

3. Use the high-resistance setting of a digital multimeter to measure

Some high-end digital multimeters have high-resistance settings and can measure larger resistance values ​​(such as tens of megohms). When using, ensure that the test environment is clean and dry to avoid interference from human body static electricity and moisture. Digital multimeters have fast measurement speed and easy operation, and are suitable for rapid on-site detection, but they still have limitations for very high resistance values ​​(hundreds of megaohms).

4. Measurement of high resistance resistance by bridge method

The bridge method is a classic resistance measurement method. The resistance value is found by comparing the equilibrium state of the unknown resistance and the standard resistance. For high value resistors, variations of the Wheatstone bridge can be used, such as the potentiometer method or the electrostatic bridge. This method has high precision, but is complex to operate and is suitable for laboratory environments.

5. Use high-impedance amplifiers with voltage measurements

After the high-value resistor is connected to the circuit, a known voltage is applied, the voltage drop is measured using an operational amplifier with high input impedance, and the resistance value is calculated. This method is suitable for integrated circuit testing and precision measurement, and can effectively reduce measurement errors.

6. Pay attention to the impact of environmental factors on measurement

High-value resistance measurements are highly susceptible to environmental humidity, temperature, and surface contamination. Before measurement, the test samples and test lines should be kept dry and clean to avoid leakage paths. The test environment should be as far away from strong electromagnetic interference sources as possible.

7. Selection and handling of measurement cables and fixtures

The insulation performance of connecting wires and fixtures directly affects the measurement results. Use high-quality insulated test wires to avoid moisture and dirt on the cable surface. The test fixture should be properly designed to ensure good contact and no additional leakage.

The measurement of high-resistance resistors is a highly technical task that requires reasonable selection of measuring instruments and methods, as well as attention to the environment and operational details. Commonly used measurement methods include the use of megohmmeters, high-impedance digital multimeters, bridge methods, and high-impedance amplifiers. Mastering these methods and combining them with actual application scenarios can effectively improve measurement accuracy and reliability. It is hoped that the introduction of this article can provide valuable reference and guidance for relevant engineering and technical personnel to solve practical problems in high resistance resistance measurement.