Glossary of Terms - R


The span of values over which a meter will function without entering overload condition, i.e., 0-150 VAC, 0-10 amps, etc.

Rated Voltage to Ground

The maximum voltage that can safely exist between the instrument measuring circuit and ground, or mounting panel. This voltage is much lower than the dielectric strength test voltage of the instrument.

Ratiometric Measurement

A technique used in some digital instruments to obtain highly accurate resistance measurements. The resistance under measurement is made a part of a resistance-ratio set, and its excitation is a self-determined fraction of the reference voltage standard used. Contact resistance and drift in the reference are thereby prevented from influencing the measurement accuracy.


The opposition presented by capacitance and/or inductance to the passage of alternating current of a given frequency.

Reactive Power (KVAR)

Power which is actually "borrowed" from the load and returned to the poser source each cycle; unused power.

Rectifier-type Meter

A DC meter equipped with a solid-state rectifier at its input to concert AC Energy to DC energy. The instrument provides measurements of the average value of an AC voltage or current, and its scale is usually calibrated in terms of the RMS equivalent. Such calibration is accurate for pure sine-wave signals, but the accuracy decreases for distorted signals.

Reference Junction

The other junction (usually at ice point) to which the measuring thermocouple junction is compared. The output voltage of a T/C is approximately proportional to the temperature difference between the measuring (hot) junction and the reference (cold) junction.


The ability of an instrument to register the same reading in successive measurements of the same input. Usually expressed as a percentage of full scale.


Electrical load or impedance device.


The degree to which nearly equal values of a quantity can be discriminated. In analog meters, the difference between the values represented by two adjacent scale divisions. In digital meters, the value represented by a one-digit change in the lease-significant digit.

Response Time (Time constant of a sensor.)

The time necessary for the sensor to reach 63.2% of step change in temperature with the sensor in water at a velocity of three (3) Ft/Sec, transverse to the sheath. (See also DPI definitions.)


A Computer interface connector used to connector serial device such as instruments for information transfer.


Resistance Temperature Detector, sensor, bulb, transducer; precision winding of copper, nickel, balco, platinum or tungsten element for temperature measurement. Connected via 2-, 3- or 4-wire hook-ups.