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Glossary
A
AC
See Alternating Current.
AC Line Frequency
The frequency of the AC power line measured in
Hertz (Hz), usually 50 or 60Hz.
Accuracy
Closeness between the value indicated by a
measuring instrument and a physical constant
or known standards.
Action
The response of an output when the process
variable is changed. See also Direct Action,
Reverse Action.
Address
A numerical identifier for a controller when used
in computer communications.
Alarm
A signal that indicates that the process has
exceeded or fallen below a certain range
around the setpoint. For example, an alarm may
indicate that a process is too hot or too cold.
See also:
Deviation Alarm
Failed Sensor Alarm
Global Alarm
High Deviation Alarm
High Process Alarm
Loop Alarm
Low Deviation Alarm
Low Process Alarm
Alarm Delay
The lag time before an alarm is activated.
Alternating Current (AC)
An electric current that reverses at regular
intervals, and alternates positive and negative
values.
Ambient Temperature
The temperature of the air or other medium that
surrounds the components of a thermal system.
American Wire Gauge (AWG)
A standard of the dimensional characteristics
of wire used to conduct electrical current or
signals. AWG is identical to the Brown and
Sharpe (B&S) wire gauge.
Ammeter
An instrument that measures the magnitude of
an electric current.
Ampere (Amp)
A unit that defines the rate of flow of electricity
(current) in the circuit. Units are one coulomb
(6.25 x 10
18
electrons) per second.
Analog Output
A continuously variable signal that is used to
represent a value, such as the process value or
setpoint value. Typical hardware configurations
are 0 to 20mA, 4 to 20mA or 0 to 5VDC.
Automatic Mode
A feature that allows the controller to set PID
control outputs in response to the Process
Variable (PV) and the setpoint.
