Resistance (R) is the property of a circuit or element that determines, for a given current, the rate at which electrical energy is converted to heat in accordance with the formula W=I2R. The practical unit is the ohm. The low resistance measurement will indicate when degradation has or is taking place within an electrical device.
Changes in the value of a low resistance element are one of the best and quickest indications of degradation taking place between two contact points. These elements include rail bonds, ground bonds, circuit breaker contacts, switches, transformer windings, battery strap connections, motor windings, squirrel cage bars, bus bar with cable joints and bond connections to ground beds.
The measurement will alert the operator to changes having taken place from the initial and/or subsequent measurements. Changes can occur from a number of influences including temperature, chemical corrosion, vibration, loss of torque between mating surfaces, fatigue and improper handling.
The Megger DLRO200-115 Digital Low Resistance Ohmmeter (DLRO) accurately measure resistances ranging from 0.1μΩ to 1Ω, at high currents, and can provide test currents from 10 amps up to 200 amps, subject to the load resistance and supply voltage.
For those applications that demand a smooth dc current, the Megger DLRO200-115 has extra filtering on the output to reduce mains frequency ripple and can drive 200 amps through a total current loop resistance of 11 milliohms. The filtered output of the unit also eliminates magnetic transients that could inductively trip a breaker’s control (bus differential relay), if left in the test circuit.
Megger DLRO200-115 features:
• Small and weighs less than 32 lbs (15kg)
• Test currents from 10 A to 200 A d.c.
• Filtered direct current output eliminates magnetic transients
• 0.1 µΩ best resolution
• On board memory for up to 300 test results and notes
• RS232 port to download stored results or for real time output to a printer
• Supplied complete with 16 ft. (5m) test leads and download software