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Also refer to: Modulating Valves; On-Off Control and
Time Proportioning Control.
Supervisor Mode
Supervisor Mode allows access to a lock-code protect-
ed sub-set of the main configuration parameters. Up to
50 configuration menu parameters can be chosen for
inclusion in using the PC configuration software.
Refer to the Supervisor Mode information in the Con-
figuration & Use section.
Also refer to: Configuration Menu; Lock Codes and
PC Software.
Thermocouple
A temperature sensor made from two different met-
als. The thermoelectric effect generates a small signal
(a few microvolts per °C) relative to the difference be-
tween the “cold” junction (at the measuring instrument)
and the “hot” junction. This does mean that the wires
and connectors used must match the metals used in
their construction. Other issues are their nonlinearity
and limited accuracy. However, basic thermocouples
are cheap to make and can measure a wide range of
temperatures. While those made from more exotic ma-
terials can even withstand the very high temperatures
found in furnaces.
The color codes for the common types are shown in
the Thermocouple Wire Identification Chart in the Elec-
trical Installation Section of this manual.
Also refer to: Input Range; Process Input and RTD.
Three Point Stepping Control
Motorized modulating valves normally require a special
“Three Point Stepping” control algorithm. This which
provides an output to move the valve further open, or
further closed whenever there is a control deviation er-
ror. When this error is zero, no further output is required
to maintain control unless load conditions change. This
type of control is use when the instrument is in Valve
Motor Drive (VMD) control mode.
Also refer to: Control Deviation; Modulating Valve and
Valve Motor Control
Time Proportioning Control
Time proportioning control is accomplished by cycling
the output on and off during the prescribed cycle time,
whenever the process variable is within the proportion-
al band(s). The PID control algorithm determines the
ratio of time (on vs. off) to achieve the level of the cor-
recting variable required to remove the control devia-
tion error. E.g. for a 32 second cycle time, 25% power
would result in the output turning on for 8 seconds,
then off to 24 seconds. This type of output might be
used with electrical contactors, solid state relays or so-
lenoid valves. Time proportioning control can be imple-
mented with relay, triac or SSR driver outputs.
Also refer to: Control Deviation; Correcting Variable;
Continuous Control; Cycle Time; PID; Primary Propor-
tional Band; Relay; Secondary Proportional Band; So-
lenoid Valve; SSR and Triac.
Trend Displays
Trend views are a standard feature on all models. They
graphically represent recent process conditions for the
control loops, showing the most recent 120 out of 240
stored data points. This data can be the process vari-
able; process variable & setpoint (shown as a doted
line) or the minimum and maximum value of the pro-
cess variable measured since the last sample. The
scaling adjusts automatically to the visible data. Any
active alarms are indicated above the graph. The user
can scroll the right hand cursor line back to examine
all 240 data points. Their sample interval and data to
display is set in display configuration.
Unlike the optional data recorder, trend views do not
retain the stored data if the power is turned off.
Also refer to: Alarm Types; Display Configuration; Op-
eration Mode; and Process Variable; Setpoint.
Tuning
PID Controllers must be tuned to the process in order
for them to attain the optimum level of control. Adjust-
ment is made to the tuning terms either manually, or via
the automatic tuning facilities. Tuning is not required if
the controller is configured for on-off Control.
Also refer to: Auto Pre-Tune; Controller; Derivative Ac-
tion; Integral Action; On-Off control; PID; Pre-Tune; Pri-
mary Proportional Band; Self-Tune; Secondary Propor-
tional Band and Tuning Menu.
Tuning Menu
The tuning menu can be accessed from the main menu.
This menu is lock-code protected. It gives access to
the pre-tune, auto pre-tune and self-tune facilities.
These assist with PID tuning, by setting up Proportional
bands, Integral and Derivative time values.
Pre-tune can be used to set PID parameters initially.
Self-tune may then be used to optimize the tuning if
required. Pre-tune can be set to run automatically after
every power-up by enabling Auto Pre-Tune.
Refer to the Automatic Tuning information in the Con-
figuration & Use section.
Also refer to: Auto Pre-Tune; Derivative Action; Integral
Action; Lock Codes; Main Menu; On-Off control; PID;
Pre-Tune; Primary Proportional Band; Self-Tune and
Secondary Proportional Band.
Triac
A small internal solid state relay, which can be used in
place of a mechanical relay for low power AC switch-
ing (0.1 to 1 amp AC). Like a relay, the output is time
proportioned. However, as solid-state devices, triacs
do not suffer from contact degradation so much faster
switching cycle times are possible, offering improved
control and reliability. A snubber should be fitted across
inductive loads to ensure reliable switch off the triac.
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