The loop resistance tester is mainly based on a requirement of the preventive test procedure for power equipment, various switch equipment, and its electrical loop resistance test. So its test current cannot be less than 100A. Because the contact surface is oxidized or the contact is not fastened, etc., the contact resistance will increase.

When a large current flows, the temperature of the contact point will rise accordingly, which will also accelerate the speed of oxidation of the contact surface, and make the contact resistance become larger and larger. If this continues, it will cause serious problems. Therefore, when necessary, the contact resistance must be measured frequently or regularly. The loop resistance tester is mainly used to measure the contact resistance loop resistance of switch control equipment.

The measurement of the loop resistance tester is relatively accurate and the practical performance is very stable. It is suitable for the on-site high-voltage switch maintenance of the power supply department and the loop resistance test requirements of the high-voltage switch factory. Conventional double-arm DC bridges are commonly used in power systems to measure the DC current of transformer coils and the contact points of high-voltage circuit breakers.

However, the test current of this type of bridge is only a level, so it is difficult to find that the cross-sectional area of the conductor loop of the transformer coil is reduced, which is a defect. When measuring the contact resistance of some high-voltage switch conductive circuits, because of the influence of the oxide layer between the oil film and the moving and static contacts, the measured resistance value will be many times larger, which masks the true contact resistance value.

The circuit constant resistance tester can make the measurement current of circuit breaker, isolating switch and contact resistance not less than 100, so this also ensures the accuracy of the measurement.