Glossary of Technical Terms

G

Gain
The amount of amplifications achieved by a device measured from its input to its output.

H

Hysteresis
The difference in signal level determined by subtracting the amount required to just turn the device off from that required to just turn the device on.

Hz
Abbreviation for Hertz, the unit for frequency; one Hz equals one cycle per second.

L

LED
Light Emitting Diode—A solid state device used for displays.

Lead Break Protection
Applicable to controller applications, circuitry senses abnormally high resistance caused by defective sensor and turns off energy source to guard against overheating.

Linearity
The closeness of a calibration curve to a specified straight line. Usually measured as nonlinearity and written as linearity; a maximum deviation between an average curve and a straight line. The average curve is determined after making two or more full range traverses in each direction. The value of linearity is referred to the output unless otherwise stated.

Load Impedance
The total of all resistance capacitance and inductance, expressed in ohms, presented to the output terminals of an instrument by the external load connected to the terminals. Output impedance is presented by the load. Source impedance is presented to the input of a device by the source.

M

Manual Reset
Reference proportioning controls only; resetting proportional band to obtain coincidence of process value and set point; necessary when load or set point is changed. Reset has no effect on percentage of proportioning band in controller.

Mercury Contactor
A special purpose contactor designed for applications with frequent cycling.

Millivolt Source
Device to generate millivolts for testing and calibration of thermocouple controller.

Modulating Controller
A temperature control device which automatically varies its output signal to attain and then maintain a set point temperature.

N

Null Balance
Exists in the circuits of an instrument when the difference between the opposing electrical quantity within the instrument and the measured signal does not exceed the dead band.

O

Offset
The steady state deviation between process temperature and set point in a proportional controller. Also called droop.

ON/OFF Control
The most simple mode of temperature control. The element is either full power or no power.

Overshoot
Exceeds maximum acceptable temperature from set point within the system.