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Control Action
This refers to the control loop(s) primary power output
direction. Reverse action is typically used with heating
applications as it increases the correcting variable as
the process variable falls. If a secondary output has
been configured, its action is always the opposite of
the primary output.
Also refer to: Control Type; Correcting Variable; Direct
Acting Control and Reverse Acting Control.
Control Enable/Disable
The PID controller outputs can be temporarily turned
off by disabling the control. When control is disabled
the setpoint value is replaced by “OFF”. All other func-
tions continue as normal. The control enable/disable
function can be controlled from the control configura-
tion sub-menu, via a digital input or optionally from the
operation menu if enabled in the display configuration
sub-menu.
Also refer to: Digital Input; Display Configuration; Op-
eration Mode and PID
Control Power Alarm
A control power alarm is based on the output from the
PID control algorithm. It can provide a warning if the
PID output rises above or falls below a set value. This
is often used in conjunction with the minimum alarm
duration time so that very brief power output peaks can
be ignored.
Also refer to: Alarm Duration Minimum; Alarm Types
and PID
Control Type
This defines if a control loop has Single (unidirectional)
or Dual (bidirectional) control outputs. Single outputs
have a primary output only. This can drive the process in
one direction (e.g. heat only, cool only, increase humid-
ity etc). Dual outputs have both primary and second-
ary outputs which can force the process to increase or
decrease (e.g. heat & cool, humidify & dehumidify etc).
Also refer to: Control Action; PID; Primary Proportional
Band; Process Variable; and Secondary Proportional
Band.
Controller
An instrument that controls one or more process con-
trol loops. For each control loop it compares a process
variable to a target setpoint, and attempts to make the
process maintain the setpoint value by applying a cor-
recting variable (e.g. turning on a heater or dosing with
alkali if controlling pH). The controller uses proportional
(P, PI, PD o PID) or On-Off control.
Also refer to: Correcting Variable; Indicator; Limit Con-
troller; On-Off Control; PD Control; PI Control; PID;
Process Variable; Proportional Control; Profiler and
Setpoint.
Controller Mode
The normal operating mode when profiling is not fitted
or it is not being used. Also refer to: Controller; Profiler
and Profiler Mode
Correcting Variable
The output level from a controller used to adjust the
process variable up or down, in order to remove any
control deviation. This might be turning on a chiller in
a temperature application or increasing the variable
speed drive of a pump in a flow application. The level
of correcting variable is commonly referred to as the
controller output power.
Also refer to: Control Deviation; PID; Primary Power
Output Limit and Process Variable
CPU
This stands for Central Processing Unit and refers to
the on-board microprocessor that controls the mea-
surement, control, alarm; display and other functions
of the instrument.
Custom Display Mode
The user can copy up to 50 Configuration Menu pa-
rameters into operation mode using the PC software.
If enabled in the display configuration sub-menu, the
configured parameters follow the normal operation
mode screens. In this mode these screens are not pro-
tected by a lock code.
Also refer to: Control Configuration; Display Configura-
tion; Lock Codes and Operation Mode
Cycle Time
For time proportioning outputs, the cycle time is the
period over which the controller averages the ON vs.
OFF time, in order to provide the required correcting
variable. Each control loop has separate cycle times
for the primary and secondary control outputs. Shorter
cycle times give better control, but at the expense of
reduce life for any electromechanical control devices
(e.g. relays or solenoid valves). Short cycle times do
not harm SSRs.
Also refer to: Correcting Variable; PID; Primary Pro-
portional Band; Proportional Control; Relay; Second-
ary Proportional Band; Solenoid Valve; SSR and Time
Proportioning.
Data Recorder
The Data Recorder option can record the process val-
ues, setpoints, alarms and events over time. Record-
ings can be transferred to a USB memory stick or via
the serial communications options for analysis in the
PC software or spreadsheets. This option includes a
battery backed-up real time clock (RTC) which con-
tinues to keep time when the instrument is powered
down.
Summary of Contents for Chromalox 4081
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