The BT51 Low Resistance Ohmmeter makes measurements by passing a current through the conductor under test and also monitoring the voltage across it. The test current is limited by a simple current limiting circuit and is measured by monitoring the voltage across a resistor. The test current is maintained at a nominal 2 A, and as the measurement is ratiometric, the reading is unaffected by any current variations.

The instrument has a 3.5 digit LED display to facilitate use in low light levels. Two LED’s on the front panel indicate battery condition and whether test current is flowing when a measurement is being made. A neon lamp indicates the presence of a dangerous voltage if the test spikes are accidentally placed across a live circuit. This warning takes place whether or not the instrument has been switched on.

The ohmmeter is protected up to 240 V a.c. by a relay circuit that keeps the instrument in a safe mode isolated from the mains supply. Again, this safeguard is effective whether or not the instrument has been switched on.

Operation of the instrument is simple, there being only one range switch to set. Power is supplied by internal rechargeable cells and the charger unit is incorporated into the case. Duplex hand spike test leads are supplied and other types of leads are available.

The instrument is built into a robust, portable case that is weatherproof and shockproof and has a hinged, detachable lid.