Glossary of Terms

 


ac
type of electrical current, the direction of which is reversed at regular intervals or cycles
ac line frequency
the frequency of the alternating current power line measured in Hertz (Hz), usually 50 or 60Hz.
accuracy
the extent to which results of a calculation or the readings of an instrument approach the true values of the calculated or measured quantities
active components
electronics components, such as transistors, diodes, electron tubes, thyristors, etc which can operate on an applied electrical signal as to change its basic characteristics ie: rectification, amplification, switching, etc.
actual
the present value of the controlled variable
alarm
a signal indicating that a process has exceeded or fallen below the set or limit point
alarm delay
the lag time before an alarm is activated
alarm module
a controller software and hardware combination configured to alert an operator or perform another function in response to a problem in the thermal system
alarm silence
feature for disabling an alarm relay output
alpha
temperature coefficient of the change in electrical resistance of a material, indicating the basic change in electrical resistance in a material for each ºC in temperature
alternating current
type of electrical current, the direction of which is reversed at regular intervals or cycles
American Wire Gauge
(AWG) a standard system for specifying wire diameter. Also referred to as the Brown and Sharpe (B&S) wire gauge
ammeter
an instrument that measures the magnitude of an electrical current in amperes
ampere
the unit of measurement of the rate of flow of electric current; one coulomb (6.25 x 10^18 electrons) per second
analog
a method of representing data using the amplitude of a signal
analog output
a voltage or current signal that is a continuous function of the measured parameter
ANSI
American National Standards Institute; a voluntary organization of manufacturing industries that publishes standards for a variety of products
ASME
American Society of Mechanical Engineers
ASTM
American Society for Testing Materials
atmosphere
the ambient environment
atmospheric pressure
pressure, in pounds per square inch or grams per square centimeter, exerted by the earth's atmosphere upon bodies located within it
auto-tune
a feature that automatically sets temperature control PID values to match a particular thermal system
automatic mode
a feature that allows the controller to set PID control outputs in response to the set point and the process variable (PV)
automatic reset
upon a certain preset condition the system is restored to the original setting
auxiliary output
an output that controls external activities that are not directly related to the primary control output
AWG
American Wire Gauge, a standard system for specifying wire diameter. Also referred to as the Brown and Sharpe (B&S) wire gauge