Watlow CPC400 - Manual (Page 78)

Chapter 3: Operation and Setup CPC400 Series User’s Guide
64 Watlow Anafaze Doc. 0600-2900-2000
What Happens if a Failed Sensor Alarm Occurs?
If a failed sensor alarm occurs:
• The controller switches to manual mode at the output
power indicated by the Sensor fail heat output and
Sensor fail cool output parameters in the Output
menu. (The output power may be different for a ther-
mocouple open alarm; see Thermocouple Open Alarm
below.)
• The controller displays an alarm code and alarm mes-
sage on the display. See Alarm Displays on page 51.
• The global alarm output is activated.
Thermocouple Open Alarm
The thermocouple open alarm occurs if the controller de-
tects a break in a thermocouple or its leads.
If a thermocouple open alarm occurs, the controller switch-
es to manual mode. The output level is determined as fol-
lows:
• If the Open T/C ht/cl out average parameter in the
Output menu is set to on, then the controller sets the
output power to an average of the recent output.
• If the Open T/C ht/cl out average parameter is set to
off, then the controller sets the output to the level in-
dicated by the Sensor fail heat/cool output parameter
in the Output menu.
Thermocouple Reversed Alarm
The thermocouple reversed alarm occurs if the tempera-
ture goes in the opposite direction and to the opposite side
of ambient temperature than expected—for example, a loop
is heating and the measured temperature drops below the
ambient temperature.
The thermocouple reversed alarm is enabled by default. If
false alarms occur in your application, you can disable the
alarm by setting the Reversed T/C detect parameter to off.
See Reversed Thermocouple Detection on page 106.
Thermocouple Short Alarm
The thermocouple short alarm occurs if the process power
is on and the temperature does not rise or fall as expected.
To enable the thermocouple short alarm, you must do the
following:
• Choose a digital input for the TC short alarm parame-
ter in the Global setup menu.
• Connect the digital input to a device that connects the
input to controller common when the process power is
on.