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