Initial Operation:
When the control has been wired you can apply power.
The display should indicate the model number, software
version and LED lamp illumination test. The
temperature (or other process variable) as measured at
the sensor should be indicated by the PV display. The
thermocouple is wired in reverse if the indicated
temperature decreases as the temperature at the
thermocouple increases. While making initial settings
to configure the control, the set point should be lowered
to a value (eg. 30°F) to assure the heaters will not be
energized. This will allow time to make any adjust-
ments of the parameters in the operators or engineering
level.
During this initial set-up, alarm points and other settings
can be made. The low limit and high limit range set-
tings (Lo.SC) and (hi.SC) should be adjusted to your
process. This sets the range (span) of the control. The
set point cannot be adjusted out of this range.
Generally, for plastics processing and packaging, a
span of 0 - 800°F is common. If oils are used, a lower
span such as 0 -300°F should be entered.
When the configuration settings have been made, you
can return to the PV/SV level. Adjust the required
process set point. The red “out” lamp should illuminate,
indicating the heaters have been powered.
Autotuning:
The autotune function “teaches” the controller the main
characteristics of the process. It “learns” by cycling the
output on and off. The process will oscillate around the
set point during autotuning. Note the diagram below:
Adjust the set point to a lower value if overshoot
beyond the normal process value may cause damage.
The results are measured and used to calculate the
optimum PID values. It should not have to be repeated
on the same process. The autotune function starts by
depressing the and keys for 4 seconds; then
release. The process value display will flash on and off
indicating the control is in the autotune mode. No other
adjustments can be made to the system while the con-
trol is autotuning. The control will finish autotuning by
itself and the correct PID values will be entered into the
control’s memory.
Autotuning will not function if the control has been con-
figured from PID to ON-OFF. For electric heating PID is
usually recommended.
Autotuning may not give satisfactory results and hold a
close temperature on all applications. If this occurs,
you can change the PID values manually using the
three charts in Figure 5.2 on the top of the next page
for a guide. It is recommended to change only one
parameter at a time, so the results of that change can
be clearly noted.
Adjusting PID Parameters:
The PID parameters can be reviewed by operating the
scroll key and noting whether the values are reasonable
or not. Examine the controller’s result. Modify the PID
values until the control quality is acceptable.
ON-OFF Control:
On-off control action is recommended when continuous
cycling of the load cannot be used. Examples are
mechanical solenoids, large contactors and valves. For
on-off control, set the following parameters to zero:
proportional band; integral; derivative and offset (oFSE).
The hysteresis (hySE) adjustment is now used to set
the deadband. The larger the hysteresis is set, the
larger the deadband will be. A large deadband will
cause the contactor (or other device) to switch less
often, but the process will oscillate farther from the set
point. This setting is measured in degrees.
Initial Period
Process Oscillates
Verifying period
PID Control
Smarter Logic + PID
Set Point
Value
PB, TI, TD
Obtained
Autotune Finished
oFSE Value
Obtained
TEMPERATURE
TIME
Process
Value
Figure 5.1 Autotuning
