Vanguard Auto-Ohm 200 S3 DC Micro-Ohmmeter

The Vanguard Auto-Ohm-200 S3 is a microprocessor-based, true DC micro-ohmmeter. It is designed for testing EHV circuit-breaker contact resistances, bushing contact joints, welding joints, or for any low-resistance measuring application. This high current and very lightweight (16.8 lbs/ 7.6 Kg) micro-ohmmeter is designed to meet the IEEE C57.09-1999 (5.15) requirement for testing circuit breaker contact resistance.

The Auto-Ohm-200 S3 can accurately measure resistance values from 1 microohm to 5 ohms. A 0.1 micro-ohm resolution is possible with current greater than 5A. The Auto-Ohm-200 S3 applies a selectable true DC test current from 1A to 200A to the resistance load to be tested.

The Auto-Ohm-200 S3 controls the test current’s rise and fall rates. The test current rise and fall rate can be selected from 5 seconds to 30 seconds. An “Auto Test” mode is also available and can be initiated simply by applying the sense cables’ leads across the two points of interest in the current path. This feature is very convenient when measuring a sequence of several resistance values in a circuit breaker contact.

The Vanguard Auto-Ohm 200 S3 can also compare test results against preset limits and determine if a test passed or failed, and a “Pass” or “Fail” fl ag is displayed accordingly. Since a true DC current (with controlled rise/ fall time) is passed through the circuit breaker contact, no magnetic transient is induced into the breaker’s current transformers. This feature greatly reduces the risk of inductively tripping a breaker control (bus differential relay).