D8 Series User’s Guide
Chapter 4: Operation and Setup
74
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 thermocouple open alarm; see Thermocouple Open Alarm below.)
• The controller displays an alarm code and alarm message on the display. Alarm Displays on
• The global alarm output is activated.
Thermocouple Open Alarm
The thermocouple open alarm occurs if the controller detects a break in a thermocouple or its leads.
If a thermocouple open alarm occurs, the controller switches to manual mode. The output level is
determined as follows:
• 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 indicated by the
Sensor fail heat/cool output
parameter in the
Output
menu.
Thermocouple Reversed Alarm
The thermocouple reversed alarm occurs if the temperature 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. Reversed Thermocouple
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
parameter 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.
RTD Open and RTD Fail Alarms
The RTD open alarm occurs if the controller detects that the positive RTD lead is broken or
disconnected.
The RTD fail alarm occurs if the controller detects any of the following conditions:
• negative lead is broken or disconnected
• common lead is broken or disconnected
• positive and negative leads are shorted
• positive and common leads are shorted
• positive, negative and common leads are shorted
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