Red Lion TCU - Manual (Page 21)

OPERATION OVERVIEW
Controller Power-up
Upon applying power, the controller delays control action and temperature
indication for five seconds to perform several self-diagnostic tests and
display basic controller information. Initially, the controller illuminates both
displays and all annunciators to verify that all display elements are
functioning. The controller then displays the programmed input sensor type
in the main display (verify that the input select sensor jumper matches the
programming). Concurrently, it displays the current revision number of the
operating system software in the bottom display. The controller checks for
correct internal operation and displays an error message (E-XX) if an internal
fault is detected (see
Troubleshooting , page 78, for further information).
Upon completion of this sequence, the controller begins control action by
displaying the temperature and updating the outputs based upon the PID
control calculation.
Controller Power Down
At power down, the steady state control value as well as all parameters and
control modes are saved, to provide a quick and predictable temperature
response on the next power-up.
When powering down the process, it is important to power down the
controller at the same time. This prevents the reset action of the controller
from shifting the proportional band while the temperature is dropping and
prevents excessive overshoot on the next process start-up.
Process Start-up
After starting the process, the controller’s PID settings must be initially
“tuned” to the process for optimum temperature control. Minimal tuning
consists of adjusting the Proportional Band, Integral Time, and Derivative
Time parameters to achieve the optimum response to a process disturbance.
The controller can be tuned once, but must be re-tuned if the process has been
changed significantly. Several options exist for tuning these parameters:
A) Use the controller’s built-in Auto-Tune feature (see
Auto-Tune , page 68).
B) Use a manual tuning technique (see Manual Tuning , page 81).
C) Use a third party tuning software package (generally expensive and not
always precise).
D) Use values based on control loop experience, calculated values or values
from a similar process.
If the controller is a replacement, the PID settings from the unit being
replaced may be used as good initial values. Be sure to consider any
differences in the units and the PID settings when replacing. The PID settings
may be fine tuned by using the techniques outlined in the PID Control section.
After tuning the controller to the process, it is important to power the load and
the controller at the same time for best start-up response.
Manual (User) & Automatic Operation
The controller can be transferred between Automatic control (closed loop;
PID or ON/OFF control) and Manual control (open loop). In the Hidden
Function Mode, the “trnf” parameter allows the operator to select the desired
operating mode. To allow front panel switching between control modes,
program the transfer (trnf) parameter to “Enbl” in the Lockout Module. The
user input or RS485 serial interface option may also be used to perform the
auto/manual transfer function, independent of the setting in the Lockout
Module.
Manual operation provides direct control of the output(s) from 0 to +100%,
or -100% to +100% if cooling output is installed. For Valve Positioner
models with slidewire feedback, this mode allows manual valve positioning.
The MAN (REM for Remote Setpoint models) annunciator flashes to indicate
that the unit is in manual operation. When transferring the controller mode
from/to automatic, the control power output(s) remain constant, exercising
true “bumpless” transfer. When transferring from manual to automatic, the
power initially remains steady but integral action corrects (if necessary) the
closed loop power demand at a rate proportional to the Integral Time. The
programmable high and low power limit values are ignored when the unit is in
manual operation.
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