DLRO100 series of digital low resistance micro-ohmmeters

The need for accurate low resistance measurement is very diverse. Typical applications include:Utilities and service contractors - commissioning new installations and regular maintenance testing of:

• Switchgear and circuit breaker contact resistance
• Busbar and cable joints
• Wire and cable resistance
• Lightning conductor bonding

Original equipment manufacturer - detecting manufacturing defects

• Production test of circuit breakers - contacts and joints
• Production test of high voltage switchgear
• Production test of welded joints and connections

Transport manufacturing and maintenance

• Railway rolling stock ground connections and manufactured joints
• Railway lines and conductor rails - commissioning and maintenance
• Aircraft frame bonds and static control

For the required values in the tens to hundreds of micro-ohms, a general-purpose ohmmeter will not give satisfactory results, even if it can nominally measure the low values of resistance involved. A kelvin type, four-wire measurement is required to calculate the low contact resistance accurately. It’s essential for the instrument to deliver a high test current; IEC requires 50 A or greater, and IEEE requires 100 A or more. A smooth DC output, including ramp up and ramp down of the current, will significantly reduce the potential of an accidental relay trip while testing. Ideally, the instrument should be suitable for use with DualGroundTM test techniques for added safety.

Megger has a wide variety of micro-ohm test equipment. The general practice for standard circuit breaker applications is to test at 100 A. By designing the unit around this current, the DLRO100 can be compact and lightweight while providing the necessary current to meet the standards. If more current is needed, Megger offers 200 A and 600 A units in the DLRO and MOM series. If you need an even smaller test instrument with test probes, Megger offers several 10 A versions of the DLRO to meet all your testing needs.

The DLRO100 is equipped with a user-replaceable, high-power Lithium-ion battery that is less than 100 Wh. This battery meets federal aviation standards for travel, so you can carry the unit on the plane with you if travelling.

If the DLRO100 has the battery option, it can still be operated off of mains power if the battery is dead or low on charge. Note: the charge time is only 2.5 hours if completely dead. So, unless you need to test all day continuously, the DLRO100 can be charged while setting up to provide enough battery to complete your work.

During its design, we had circuit breaker testing directly in mind. Therefore, the DLRO100 provides an authentic, smooth DC output with ramp-up and ramp-down current at the beginning and end of the test to minimise unwanted tripping on parallel equipment that is still in service.

You can order the DLRO100 with 5, 10, or 15 metre lead lengths that are CAT IV 600 V rated. When other lengths or clamps are required, the DLRO100 has a terminal adapter plug in which a spade-type connector can be attached for custom current cables. The voltage sensing leads use standard banana jacks.

All DLRO models offer a choice of test modes. Manual mode allows you to initiate the test once the probes are in contact with the object under test. When you press the test button, the instrument performs a single test. In “Auto” mode, as soon as you connect the potential leads, the test starts automatically. To repeat a test, you must break and remake contact with the potential leads. In “Continuous” mode, you connect the test leads and press the test button. The instrument will continue to test, updating the display after each new test cycle until you press the test button again. With the simple keypad and rotary switches, you can operate all the DLRO100s with work gloves on.