Polar Toneohm 550

The 550 TONEOHM is a precision milliohmeter with a unique resistance-dependent, variable-frequency audio tone output.

The 550 is ideally suited for electronic manufacturing and service industries as a short circuit and fault-finding aid. The highly sensitive variable-frequency audio tone output makes it ideal for locating the physical location of short circuits on PC boards and within system wiring. In many cases, shorts may be located to within 0.2 inches of the actual fault location, without the need to disconnect associated components or wiring.

Frequency resolution of the audio tone is accurately dependent on the resistance between two hand-held Kelvin probes. If the probes are placed on two tracks of a PC board and a tone is heard, the tone indicates there is a short circuit between the two tracks. By moving one of the probes along its track until the tone reaches its highest pitch, the precise location of a short can be found.

The highly accurate 550 allows the TONEOHM to be used for other varied applications including continuity testing, relay and switch contact measurements, detection and measurement of high-resistance connections, measurement of transformer winding resistance, and the determination of partial shorts between windings. The low probe tip injection voltage (60mV max., 5mV typ.) prevents possible damage to sensitive semiconductor devices within the circuit under test. Kelvin probes, in combination with DC injection, avoids measurement errors which could result from parallel capacitors or lead loss.