# 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.

### OFHC

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

### OHMS/Volts

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).

### Opto-Isolator

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