Resistance Tester Selection: Measurement Methods for Low Resistance and High Resistance

This article introduces the selection method of resistance testers. Based on the resistance value range of the tested object, low resistances (less than 1 ohm) require the four-wire Kelvin method, using constant current and voltage measurement to eliminate the effects of contact resistance; high resistances (greater than 1 megohm) are measured using the voltage method to detect small currents, with attention to shielding and leakage prevention. The article also mentions parameters such as test current and resolution, as well as environmental and safety considerations.

Key points of selection

The selection of resistance tester should determine the measurement principle according to the resistance value range of the measured object: low resistance usually refers to <1Ω, which needs to eliminate the influence of contact resistance; high resistance usually refers to >1MΩ, which needs to avoid leakage current interference. The following are two types of methods.

Low resistance measurement method

The four-wire Kelvin test method is used: two wires provide constant current I, and two wires measure voltage drop V. The measured resistance R=V/I, the formula is as follows:

R = V / I

This structure eliminates lead resistance and contact resistance. Typical test currents range from 1mA to 10A. Attention should be paid to current direction switching to eliminate thermal EMF and voltage drop should be measured by differential inputs. It is suitable for wires, connectors, relay contacts, etc.

Table: Key parameters for low resistance testing

Parameters	Scope example
Test current	1 mA - 10 A
resolution	0.1 μΩ
Precision	± 0.05% reading

High resistance measurement method

Using the DC voltage method or charging method: apply a known voltage U and measure the tiny current I, R=U/I. High impedance amplifiers and shielded cables are required.

R = U / I

Common modes include constant voltage method and ramp voltage method. The constant voltage method is used for insulation resistance, and the ramp method is suitable for capacitive objects. The measuring range is up to 1MΩ-10TΩ. Pay attention to environmental humidity and electric field shielding.

Table: Key parameters of high resistance testing

Parameters	Scope example
Test voltage	10 V - 1000 V
Current resolution	1 fA
Resistance range	1 MΩ - 10 TΩ

Environment and safety

Low resistance measurement requires clean contact surfaces and no oxide layers. High resistance measurements should be made using a three-axis cable and a grounding guard ring, and the instrument should be warmed up for 30 minutes. All operations must be disconnected from the power supply of the test piece and discharged.

Quote the instructions

1. Principle of low-resistance four-wire method: refer to the relevant standard documents of the International Electronics Commission. 2. High resistance measurement methods: Based on a literature review of insulation testing techniques. 3. Parameter range: synthesize the general data of multiple industry application articles.