Video: RMO-H

Video transcript

What the RMO-H measures, why a battery-powered micro-ohmmeter changes the way a breaker is tested, and how it is connected, from a bucket lift, or from the ground. Contact resistance is measured with high direct current, and that has meant a heavy instrument on the ground and long, thick cables up to the breaker. The RMO-H weighs 0.95 kg, runs on its own battery, and goes up to the breaker with the operator. Up to 300 A of regulated direct current, chosen from 1 A upwards.

Readings from 0.1 micro-ohm to 3,000 milli-ohms, with the same typical accuracy as the mains-powered models, in a body of 0.95 kg. Six models in two sub-series. The first three have a one-cell battery, and work with short leads. The other three have two cells, double the output voltage, and drive leads of 5 meters, or more. Each sub-series has its own lead sets. They are not interchangeable.

Everything is on one face, made for one hand. The display shows the current and the memory position. The Omega key starts the measurement, and the arrows set the current. The two terminals on the sides take the combined current and sense leads. The current comes from a lithium polymer battery, not from an ultracapacitor. So there is no wait between tests. The current does not drop during the reading, and it does not depend on the object. One charge gives up to 3,000 tests at 50 amps, or 600 at 300 amps.

ships with the PC software, an earth cable, carrying straps, and a plastic case. The recommended leads combine current and sense in one cable with TTA clamps. Kelvin probes with a trigger button, battery clamps, test shunts, the car charger, and a spare battery are options. The connection follows the four-point Kelvin method. Current leads at the outer points, sense leads inside them, as close to the object as possible, so that cables and clamps stay out of the result.

With the combined leads, each clamp carries both. With short leads, the operator takes the RMO-H up in the bucket and clamps straight onto the terminals of each interrupter. One click, and the reading is taken. The breaker is earthed on both sides, and one earth lead also serves as the sense return. Some utilities require testing from the ground, with leads longer than 5 meters. The higher output voltage of the RMO-H 21, 22, and 23 keeps the current up

through those leads, without the heavy cables a long run usually needs. On medium voltage breakers, the Kelvin probes with a trigger button are the quickest way. Each probe carries current and sense, and the button on the probe starts the test, so the operator never has to reach for the instrument. can also measure with the breaker earthed on both sides, with the same connection as with one side earthed. Part of the current then flows through the earth leads,

so the reading may be slightly less accurate than the standard measurement. Select the current, attach the clamps, and press omega. The current rises along an automatic ramp, is held while the voltage drop is measured, and ramps back down. The ramps keep magnetic transients out of the reading, and the result is stored with its date and time. With RMAX enabled, the RMO-H flags any reading above the limit set by the user, a pass or fail check on the spot.

The internal micro SD card keeps up to 10,000 readings with date and time, and the PC software downloads them over Bluetooth. It suits any low, non-inductive resistance, breakers and switchgear, disconnectors and bus bar joints, conductor terminals on high voltage lines, welds and cable splices, offline tap changer contacts, railway rails, and bonds in aircraft. Circuit breaker testing from Amperis.