Glossary of Loop Calibration Terms
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.
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 measuring a fractional part of one of the divisions of the fixed scale.
