ControlLogix T04:C34 (Timer Failure) after a recipe download, what to check?
I'm getting a Major Fault T04:C34 (Timer Failure) on our ControlLogix controller. It seems to happen right after an operator downloads a new recipe. What should I be looking for first?
A Major Fault T04:C34, also known as a 'Negative Timer' fault, indicates that a timer instruction in the Logix 5000 controller program received a negative value for its preset (.PRE) or accumulated value (.ACC). This fault occurs when the timer instruction attempts to execute with this invalid negative value. The controller status display will show 'Major Fault T04:C34 Timer Failure'.
Likely causes and checks
1Preset or accumulator written from an HMI, recipe or message
- Points to it
- The fault follows an operator entry or recipe download, suggesting that the negative value originated from an external source like an HMI or recipe system.
- Check
- Check the source value from the HMI or recipe and add a range check in both the HMI interface and the controller program to ensure only non-negative values are written to the timer's preset or accumulator.
2Preset written from a calculation that can go negative
- Points to it
- The timer's preset (.PRE) might be set by a MOV or CPT instruction from another value, such as a difference or a scaled input, which could result in a negative outcome.
- Check
- Find every write operation to the timer's .PRE tag in the program and ensure that the result of any calculation is limited to zero or a positive value before being written to the timer.
Next check: The fault message will name the program and routine where the fault occurred. While the timer tag is in the faulted rung, the problematic negative value is often written to it from elsewhere in the program. Cross-reference all writes to the timer's .PRE and .ACC tags to identify the source of the negative value.
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