Microhmmeter QMOM 600

Microhmmeter QMOM 600

The QMOM-600 is specifically 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 (33 lbs/ 15 Kg) micro-ohmmeter is designed to meet the IEEE C57.09-1999 (5.15) requirement for testing circuit breaker contact resistance. The QMOM-600 can accurately measure resistance values from 1,5 micro-ohm to 450 milliohms. A 0.1 micro-ohm resolution is possible with current greater than 10A. The QMOM-600 applies a selectable true DC test current from 10A to 600A to the resistance load to be tested.

The DMOM-600 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 DMOM-600 can also compare test results against preset limits and determine if a test passed or failed, and a “Pass” or “Fail” flag 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).

Dual Ground Option

With the Dual Ground option, the QMOM-600 can also measure the circuit breaker contact resistance with both sides of the breaker bushing being grounded. When a test current is applied to a circuit breaker with both sides grounded, some of the test current flows through the safety ground cables. Using an external current sensor, the QMOM-600 measures and eliminates this current from the total test current. It then calculates the actual resistance value of the circuit breaker.

Test Record Storage

The QMOM-600 can store 128 records of 64 readings internally, and up 999 test records on an external USB Flash drive. Test header information (Company, Substation, circuit breaker
ID’s) can also be entered using the 44-key keypad and is stored with each test record.

User Interface

The QMOM-600 features a back-lit 128 x 64 pixel LCD screen that is viewable in both direct sunlight and low light levels. The resistance readings are displayed in a large font on the LCD screen in micro-ohms or milliohms. The unit is operated via a convenient 44-key “QWERTY” keypad on the front panel.

Included Cables

The QMOM-600 is furnished with a 15-ft (#1/0 AWG) test cable set. Custom test cable lengths are optionally available. Optional heavy-duty, welding type C-clamps are also available allowing the user to connect the test leads to a wide variety of bushing sizes, bus-bars, or large conductors.

Built-in Thermal Printer

The DMOM-600 features a built-in 2.5" wide thermal printer that can be used to print test reports in the field.

Computer Interface

Windows®-based analysis software is provided with each unit and can be used to remotely control the QMOM-600 via the RS-232C port. Using this software, the user can retrieve test records (from the unit’s memory or a USB Flash drive), analyze test results, and print test results on a desktop printer. Test records can also be exported to PDF, Excel, and XML formats for further analysis.

QMOM-600 Specifications


Portable micro-ohmmeter

Physical specifications

16¾”W x 12½”H x 12” D (42.7 cm x 32 cm x 30.5 cm); Weight: 33 lbs (15 kg)

Input power

100 - 240 vac, 50/60 hz

Resistance reading range

1.5 milliohms at 600A to 450 milliohms at 10A


10A to 49.9A: 1% ±2 micro-ohms

50A to 600A: 1% ±1 micro-ohm

Test current range

10 Amperes to 600 Amperes (selectable in 1A steps); Thermally protected DC power supply


Back-lit lcd screen (128 x 64 pixels); viewable in bright sunlight and low light conditions


Rugged, 44-key "QWERTY" membrane keypad

Internal test record storage

128 test records. Each record can contain up to 64 readings

External test record storage

Up to 999 test records on external USB flash drive.

Computer interface

One RS-232C PC interface


Built-in 2.5" wide thermal printer

Pc software

Windows®-based analysis software included with purchase price


Designed to meet IEC 61010 (1995), UL 61010-a, and CAS-C22.2 standards


Operating: -10°C to +50°C (+15°F to +122°F); Storage: -30°C to +70°C (-22°F to +158°F)


90% RH @ 40°C (104°F) non-condensing


2,000 m (6,562 ft) to full safety specifications


15 ft (4.6 m), #1/0 AWG test cables, power cord, ground cable

Optional accessories

shipping case, 30 ft (9.1 m) test cables, C-clamp set, hand spike set, dual ground option


1 year on parts and labor

NOTE: the above specifications are valid at nominal voltage and ambient temperature of +25°C (+77°F). Specifications are subject to change without notice

Connections Microhmmeter QMOM 600Test result Microhmmeter QMOM 600Controls Microhmmeter QMOM 600

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