Watlow PC1X-F20, User Manual

Page: 26 / 73

Heater Bakeout
If a system is shut down for long periods, some
heaters can absorb moisture. With a standard power
controller, turning the power full “on” when mois-
ture is present, can cause the fuses or the heater to
blow. However, with the Power Series you can now
“bake out” the moisture in a wet heater before
applying full power and destroying the heater.
During heater bakeout, the Power Series slowly
increases voltage to the heater while monitoring the
output current. If the heater achieves full output
before the bakeout time expires, then the heater is
dry and can be put into service. At all times, the out-
put will not exceed the temperature controller set
point.
If the output current reaches a user-specified trip
point during the bakeout (as it would if arcing
occurred in the heater), then the Power Series shuts
off the output and activates an over-current trip
error,
[HbOC] . The operator should then lengthen
the bakeout time and restart or just restart, depend-
ing on how long the initial bakeout ran. To start
heater bakeout you must cycle the controller power.
After a successful heater bakeout, the Power Series
automatically switches to the operator pre-selected
control mode (phase angle or zero cross).
NOTE: Heater bakeout is intended for magnesium oxide
filled nichrome elements. A nichrome element heater can
have a tolerance up to ± 10%. This tolerance could add to
the maximum heater current during normal operation. For
example, a 50-amp heater could draw 55 amps and still be
a good and dry heater.
Heater bakeout may be selected in single phase
(phase to neutral) and 3 phase, 6 SCR systems with
any pre-selected control mode. You must also have
the heater diagnostics option installed on your
Power Series.
Heater bakeout operates with an over-current trip.
The operator must set the maximum current
allowed during heater bakeout using the
[HbOC]
prompt. This will set the maximum allowable load
during heater bakeout.
Setup Page:
• Enter the Setup Page by holding ± ¬ for 2 seconds.
• When the display reads [algo] , press Î until [Opt1]
[`set] [`set]
is displayed. Press ®
until
[`Off] is displayed.
[`Hbo]
Use the Ó Î keys to turn heater bakeout on.
• Press ®
until
[Min] appears in the lower display.
Use the Ó Î keys to set the desired heater bake-
out time in minutes.
• Press ®
until
[`HbC] appears in the lower display.
Use the Ó Î keys to set the desired maximum
load current during the heater bakeout process.
NOTE: Repeat this procedure for each zone that you wish to
configure.
Figure 5.4a— Heater bakeout.
100%
60%
0%
Output P
ower
Time
Temperature Control
Command Signal
Process Set Point
5 . 4
■
Wa t l o w P o w e r S e r i e s F e a t u r e s , C h a p t e r 5
Heater Tolerance Detection
Heater tolerance detection allows you to detect a
failed heater or a heater that is beginning to fail. An
alarm is triggered if the load current drops below or
rises above specific levels.
For example, if you have five heaters that draw 20
amps each, for a total load current of 100 amps at
100 percent power, you could program the heater
tolerance alarm to trigger if the load current drops
below 80 amps at 100 percent power. This would
indicate that one of the heaters has failed (open.)
To monitor for a heater that is beginning to fail or
age, you could watch for too little or too much cur-
rent. For example, in Figure 5.4b the alarm is pro-
grammed to trigger if the load current drops below 90
amps, or rises above 110 amps at 100 percent power.
The Power Series automatically adjusts the set
points, depending upon the percent power, as shown
in the illustration below.
Figure 5.4b— Heater Tolerance Detection.
Percent Power
100 75 50 25 0
Amps
Heater
Tolerance Low Set Point
Heater
Tolerance High Set Point
Load Current