Megger DLRO200-115 – Digital Low Resistance Ohmmeter

The DLRO200-115 is designed to check and measure contact resistance in high voltage circuit breakers, disconnecting switches (isolators), busbar joints, or for any low resistance measurement. The test set accurately measure resistances ranging from 0.1µ-ohm to 1 ohm, at high currents.

This versatile instrument 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 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 DLRO200-115 also eliminates magnetic transients that could inductively trip a breaker’s control (bus differential relay), if left in the test circuit.

The unique design allows the weight and size of the DLRO200-115 to be kept to a minimum; the instrument weighs less than 32 lbs. (14.5 kg). This small size plus a water/dust ingress rating of IP54 makes the test set equally at home in the workshop, on the production floor or in the field.

300 sets of results may be stored in the test set’s on-board memory for later download to a PC or may be outputted directly to a printer via the RS232 port. You may also add notes to any stored result by using the on-board alphanumeric keypad, thereby making later identification of results easier to determine.

As well as adding notes to stored results, the alphanumeric keypad allows you to set the test current directly by keeping in the value required. The DLRO200-115 will check the continuity of the test circuit, and will quickly ramp the test current up to the desired level. The keyboard is also used to set upper and lower limits for the result and to prevent the use of excessive currents by setting an upper limit to the allowable test current.

The DLRO200-115 uses a four terminal measurement technique to cancel the resistance of the test leads from the measurement. The test set operates in one of three modes, which are simply selected from the on-screen menu.

CONTINUOUS mode is provided for users who wish to monitor a resistance over a period of time. Connect the test leads, select the test current and press the TEST button. The DLRO200-115 will pass a current continuously, and measure the load resistance at 2 second intervals, until the test button is pressed to stop the test or the test circuit is interrupted.

Measuring individual joints in a busbar is a good example of the convenience to be gained by using AUTO mode. The two current leads are connected to the ends of the busbar. They will remain connected there until all tests have been completed. When the voltage leads make contact across a joint, the DLRO200-115 detects that all four leads are connected, carries out a test and stops. When you move to the next joint the DLRO200-115 detects the already completed circuit automatically and carries out the next test, and so on until all joints have been tested. The results may be stored automatically and may be recalled to the display or downloaded for review.