Other PID settings
CNT-SVX12C-EN 71
Other PID settings
You can also use these settings to manage PID loops:
• Proportional bias, which takes the place of derivative gain in propor-
tional-only control
• Minimum and maximum output, which limit the range of output of
the PID algorithm
• Enabled and disabled modes, which enable the PID output or disable
it to a default value
• Fail-safe mode sets the PID output to a “safe” value if the hardware
input that provides the process variable fails.
For more information, see BAS-APG002, PID Control in Tracer Multi-
Purpose Controllers.
Troubleshooting procedure
IMPORTANT
Remember to change only one thing at a time.
Follow these steps to troubleshoot a PID loop:
1. Make sure that the system is not in override.
2. Graph the process variable, setpoint, and valve position over time to
determine how the system performs.
Look at the big picture. Can the system do what’s expected of it? What
is happening to the process variable? Is it oscillating or failing to
reach setpoint? Is the output oscillating?
3. Check for failure conditions that are always true.
4. Check PID settings for:
• Output minimum incorrectly set to 100%
• Output maximum incorrectly set to 0%
• Sampling time that is too fast or too slow
5. Check the system for disturbances from:
• Bad actuator linkages
• Faulty sensors
6. Change PID gains.
• Reduce gains if experiencing system overshoot, output at mini-
mum or maximum, or cycling of output around setpoint
• Increase gains if experiencing system undershoot
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