14 96VTR Ver. 2.0 11/99
Appendix B: Application Programming Example
(Refer Fig.5).
The aim is to maintain an
oven temperature of 500
o
F. The
controller monitors the oven temperature
via the thermocouple. The controller
compares the actual temperature (PV) to
the desired temperature (500
o
setpoint
SV) and throttles the heater as needed
to maintain 500
o
F. If the oven
temperature reaches too high, the
controller's alarm output can trigger an
audio or visual alert. The alarm contact
can also be used to switch on/off an
external device such as a master switch
or cooling fan. In this example, the alarm will trigger an annunciator at 600
o
F. To program
the controller to perform the task described above, refer to the steps below. The
parameters not listed below are either inconsequential with regard to this example or they
will not appear on the controller display due to the controller configuration. Use the
programming level sequence shown below (i.e., Level 3 then Level 1. etc.)
Programming Level 3
A1Fu
(Alarm Function): Set to '2' which is an absolute alarm meaning that the alarm is
fixed. In this case the alarm will be fixed at 600
o
F. This 600
o
F value is
programmed later in the procedure.
A1HY
(Alarm Hysteresis): Set to '0'. Hysteresis is similar to 'deadband'. A region
extending from the alarm setpoint up or down, depending upon the alarm type,
where no relay action can occur to eliminate relay chatter.
Act
(Action): This is control output action. Set to '1' for heating.
unit:
Set to '1' for
o
F
dp
(decimal point): Set to '0' for no decimal point
Ct
(Cycle time):
To start off with, set to approx. 6 seconds. This can be re-adjusted later
after the process is observed. Cycle time is the rate at which the controller will
make adjustments to the heater. Set for the longest time possible (to save relay
life) without causing process oscillations.
tYPe:
Set to '1' for a K Type Thermocouple
LoLt and HiLt
(Low Limit / High Limit): Set these to 0
o
and 1000
o
respectively. This is
simply a span setting.
Programming Level 1
A1SP
(Alarm Setpoint): Set to 600
o
F. Temperature at which the alarm relay will switch on the
alert annunciator.
Tuning the Controller (Level 2 parameters)
The best plan of attack with tuning is running the Auto Tune utility. Auto Tune will
automatically program the controller to respond with little process oscillation around
setpoint and minimal overshoot on oven heat-up. Run the Auto Tune utility per section 9.2
in this manual. Running Auto Tune supersedes programming Level 2 parameters.
Calibration (Level 4 parameters)
Calibration is very rarely required. If calibration must be performed refer to Section 9.1 for
details or contact Extech.
Heater
Oven
96VTR
K Thermocouple input
Control Output
Compares oven
temperature with
desired setpoint
and adjusts heater
(Adjusts Heater)
(Measures oven temp.)
Alarm Annunciator
Alarm Output
Figure 5
