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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 displays
basic controller information. Initially, the controller illuminates both displays
and all annunciators to verify that all display elements are functioning.
Following, the controller 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).
A profile can be programmed to Start (run mode), Stop (off mode), or Pause if
it was running on power-up (see "Profile Power Cycle Status Parameter"
section).
Upon completion of this sequence, the controller begins control action by
displaying the temperature and updating the outputs based upon the PID control
value.
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, which 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. Tuning consists of
adjusting the Proportional Band, Integral Time, and Derivative Time parameters
to achieve the optimum response to a process disturbance. Once the controller is
tuned, it may need to 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).
B) Use a manual tuning technique (see manual tuning).
C) Use a third party tuning software package package (generally expensive and
not always precise).
D) Use values based on control loop experience 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 transfered between Automatic control (closed loop; PID
or ON/OFF control) and Manual control (open loop). Placing the controller in
the Manual Mode does not impede the advancement or operation of a running
profile. 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 RS-485 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. The MAN (manual) annunciator
flashes to indicate that the unit is in manual operation.
In the Manual Mode, the output power can be adjusted using the front panel
arrow buttons when % output power is viewed in the lower display. If the %
output power is locked or read only, then the output power can be adjusted in the
unprotected parameter mode when OP is viewed. With the serial option, the %
output power can be modified independent of what is viewed in the display as
long as the unit is in the manual mode.
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 will correct (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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