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The Auto-Ohm 100 S2 is Amperis third-generation, microprocessor-based, true DC micro-ohmmeter. It is designed for testing EHV circuit-breaker contact resistances, bushing contact joints, or for any low-resistance measuring application. The Auto-Ohm 100 S2 can accurately measure resistances ranging from 1 micro-ohm to 300 milliohms. It can output a test current from 10 Amperes to 100 Amperes.
The Auto-Ohm 100 S2 applies a true DC current from 10A to 100A to the resistance load to be tested. Any test current setting can be selected by using the function control knob on the front panel. The Auto-Ohm 100 S2 controls the test current's rise and fall rates by using a switching DC power supply and a current regulator circuit. An Auto Test Mode is also available and can be initiated simply by applying the sensor cables' leads across the two points of interest. This feature is very convenient when measuring a sequence of several resistance values in a breaker contact.
Since a true DC ramped current is passed through the breaker contacts, no magnetic transient is induced into the breaker's current transformer. This can prevent the risk of inductively tripping a breaker control (bus differential relay). The resistance reading is displayed directly in micro-ohms or milli-ohms. No calculations are required to compensate for lead resistances when using the Auto-Ohm 100 S2.
The Auto-Ohm 100 S2 features a back-lit LCD screen (1-inch high, 16 characters by 2 lines) that is viewable in both bright sunlight and low-light levels. The resistance reading is displayed on the screen until the next test is initiated. The last three resistance measurements are stored internally and can be displayed on the LCD screen. An RS- 232C interface port is also provided for factory calibration and diagnostic testing. The Auto-Ohm 100 S2 is furnished with two 30-foot test cables. Fifteen-foot test cables are also available as an option. Both cables are terminated with quick disconnect clips. Heavy-duty, welding-type, C-clamps are available as an optional accessory. These can be used to connect the test cable leads to a wide variety of bushing sizes, bus-bars and other conductors requiring low-resistance test contacts.