4-20 mA loop - A 4-20 mA signal that is representative of a process variable or a control signal that controls a process variable.

Compliance voltage - The voltage a current source develops when attempting to drive a mA signal through a resistive load.

DMM - Digital multimeter.

Electronic valve positioners - Devices that can control the flow in a process with input from a mA or digital control signal.

Ground loop - A difference in potential (voltage) between (2) signal grounds.

Linearity - The closeness of a calibration curve to a specified straight line. Linearity is expressed as the maximum deviation of any calibration point from a specified straight line.

Loop-powered isolator - A device that produces an electrically isolated mirror image of the input side 4-20 mA current.

mA - Milliamp; a unit of electric current equal to one thousandth of an ampere.

Precision current shunt - A conductor joining two points in a circuit to form a parallel circuit, through which a precision voltage can be measured or derived.

RTD - Resistance temperature device, a temperature measurement sensor that has predictable changes in resistance with a change in temperature.

Signal conditioner - A circuit to modulate a signal so as to make it intelligible to, or compatible with, another device, including such manipulation as pulse shaping, pulse clipping, compensating, digitizing, and linearizing.

Strain gauge - A measuring element for converting force, pressure, tension, etc., into an electrical signal.

Thermocouple - A junction of dissimilar metals that generates a small voltage correlated to the temperature of the junction.

µA or uA - Microamp; a unit of electric current equal to one millionth of an ampere.

Vernier - A small, movable, graduated scale running parallel to the fixed graduated scale and used for