Thermal Monitoring and Thermal Fault Behavior
The controllers can monitor internal module temperatures and act as the temperature increases.
IMPORTANT:
If you follow the recommended limits for ambient (inlet) temperature and apply the required clearances around the chassis, the controller should not reach the initial warning (minor fault) temperature. See the 1756 ControlLogix and GuardLogix Controllers Technical Data, publication 1756-TD001.
Thermal Monitoring
Item | Description |
|---|---|
A | Threshold for controller to declare a `T17:C35 Controller internal temperature is approaching operating limit’ minor fault and set the Diagnostics minor fault bit. The fault is recorded in the minor fault log but is not displayed on the front panel. If the temperature returns to an acceptable range, the Diagnostics minor fault bit clears, but the minor fault record remains. |
B | Threshold for the controller to declare a `CPU Temperature Fault’ major recoverable fault. If a fault handler does not clear the fault, then the module enters fault mode, records the fault in the major fault log, and displays `T17:C34 CPU Temperature Fault’ on the front panel. |
C | Hardware Preservation Hysteresis Limit. |
D | Power does not become enabled when in this range. |
E | Threshold for the controller to declare a `Hardware Preservation Fault’, resetting the module and disabling power. In the disabled power condition, only the OK status indicator is illuminated, and it is red. The module does not apply power until it has cooled below the Hardware Preservation Hysteresis limit. The module then enters fault mode, records the fault in the major fault log, and displays `CPU Temperature Fault’ on the front panel. |
F | All power to the controller is disabled except to run the red OK status indicator and monitor the temperature. |
IMPORTANT:
The presence of any temperature warning indicates that you must act to reduce the ambient temperature of the module. Instructions for using relay ladder logic to check for a minor fault can be found in the Logix 5000 Controllers Major, Minor, and I/O Faults Programming Manual, publication 1756-PM014. A GSV instruction can read the MinorFaultBits attribute of the FaultLog class name. If the Diagnostics minor fault bit (Bit 17) is set, then a temperature minor fault can be present. Check the Minor Faults tab of the Controller Properties dialog box in the Logix Designer application to see if the minor fault is a temperature warning.
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