Appendix C: Heater Break Option - Fuji Electric PXZ Series Operation Manual

Time
Constant
PV
4. Widen the Proportional Band until only slightly unstable. This is the
Proportional Band's Ultimate Sensitivity. The Proportional Band's
Ultimate Sensitivity width will be defined as "P" when calculating
the actual Proportional Band.
5. Use the following coefficients in determining the correct PID set-
tings for your particular application.
Control P
Action Setting Setting
P Only 2P
PI 2.2P
PID 1.67P
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Time
I D
Setting
* *
.83T *
.5T .125T
APPENDIX C
Heater Break Option
The Heater Break Option is used to detect heater break conditions
and to energize an alarm relay when such conditions exist. In most
cases, the option is used to detect the failure of one or more zones in
a multi-zoned heater where all individual resistive heater zones are
wired in parallel. Failed heater zones would create cold spots in a
system which could hamper the process and even ruin the product. If
cold spots in a system are a problem, the Heater Break Option is an
effective way of alerting the operator of a heater break condition, a
cause of cold spots.
The PXZ controller is able to detect a heater problem by analyzing the
current used by the heater. The actual sensing is done by a current
sensing transformer, sold separately, which is placed around the hot
lead going to the heater and connected to the controller. The signal
sent by the current sensing transformer is timed with the output of the
PXZ. When the output is energized the signal sent from the current
sensing transformer is analyzed. When the output is de-energized the
signal sent from the current sensing transformer is not analyzed. This
eliminates the alarm condition turning on and off due to the output
condition of the controller. If the signal sent when the output is ener-
gized indicates that the current level is below what the Heater Break
alarm is set for, the alarm is energized. The alarm is non-latching.
Notes:
1. The Heater Break Option is available on the PXZ-5, 7, and 9
controllers only.
2. The Heater Break Option cannot be used on the PXZ controller with
a 4-20mA DC output. The current sensing transformer would pick
up current changes due to fluctuating power output, between 0%
and 100%, which would result in a heater break alarm condition
even though no such condition existed.
3. The Cycle Time must be set at 6 secs. or higher in order for the
controller to correctly analyze the signal sent by the current sens-
ing transformer.
4. The power supply used should be the same for the PXZ and heater
to eliminate current fluctuations due to power differences between
different power supplies.
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