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Once you see the oscillation, back the integral gain down by 0.05 – 0.1. Start the pump again and make sure that the
flow rate does not overshoot the set point significantly.
Note: you may want to use a stopwatch to time how long it takes to get to 80% of the set point, especially if you are using the
PulsaGuard pump protection. PulsaGuard will stop the pump if the minimum flow is not reached within the timeout limit. In
any case the pump should be able to get to at least 90% of the given flow set point within 25 seconds.
Step 5 – Tune the derivative gain
The derivative gain is not required under all circumstances. In many cases, a PI controller alone is sufficient to
control the pump flow. If derivative gain is added, start with a low setting (0.05 or so) and keep adjusting in 0.05
increments until desired settling time is met.
22.5
Troubleshooting
My flow rate is never reached. How can I fix it?
If the flow rate is never reached you have what is called an over-damped system. Try increasing the Integral gain to
help pull the set point up higher. Also, make sure your flow rates and units match. If you are trying to set a flow
higher than the pump can provide, you'll never reach it!
My flow goes past the set point and back below again and oscillates a long time. How can I fix it?
Some oscillation is natural in many PID controlled systems. To minimize it you need to decrease the Proportional
and/or Integral gains to slow the system down a bit.
105
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Table of Contents
Troubleshooting
