Glossary of Terms - O

O.D. (Tubing VS. Pipe)

Outside diameter, the proper way to size T/C or RTD sheath tubing vs. inside diameter used for pipe sizing.

Offset Current

The difference between two bias currents drawn by the inputs of a differential input stage of an electronic meter.

Offset Voltage

The deviation from zero output voltage of an amplifier having zero input voltage.


Oxygen free high conductivity copper, one leg in type T thermocouples, the other leg being an alloy of approximately 60/40 copper nickel.


Relates to total terminal resistance of voltmeters. For example, a meter with 1000 ohms/V, and 300 volts full scale has a total resistance of 3000,000 ohms, using ohms law l=E/R or 1V/1000 ohms = 1 MADC

OHMS Per Volt

Indication of the total terminal resistance of an analog voltmeter. A measure of the sensitivity of an analog voltmeter. A 1000-ohms-per volt instrument has resistance of 150,000 ohms on its 150 volt (full scale) range, and 300,000 ohms on it 300 volt range. Its basic movement is a 1-milliampere meter (1 = E/R = 1/1000 = .001A = 1 milliampere).


An isolation device that provides an electrical barrier between related circuits.


The excel load beyond full-scale value that an instrument can withstand without damage or failure. Expressed as a percent of a full-scale value.

Over Range

In digital meters, a reading that exceeds full-scale (but is less than an overload) that does not require switching to a high range, i.e., for 31/2 digit DPM 0-999 is full-scale rating. 1000-1999 is over range. 2000 and up is overload.


The ratio of the overtravel of the pointer beyond a new steady deflection to the change in steady deflection when a new constant value of the measured quantity is suddenly applied.