I do a lot of hot water set projects, which are simply a steam heat exchanger with a steam control valve that adjusts to a PID setpoint- the water outlet temperature. These are often controlled by MicroLogix 1400s. Lately I've been experimenting with using feed forward to adjust the CV output based on water flow rate, as the greater the water flow, the more steam is required to maintain temperature. This greatly improves the performance of the PID, but leaves me with two questions:
1. What the heck are the units for feed forward in a Logix 500 PID? The manual includes a whole single sentence on using feed forward, and doesn't cover units as far as I can tell.
2. Is there a clean way to include a deadband for the FF to avoid jitter? In my hot water sets, the flow rate is constantly changing slightly, as flow does naturally, which causes the control valve to constantly make unnecessary slight adjustments, which increases wear. How do y'all handle it for situations like that?
Thanks!
1. What the heck are the units for feed forward in a Logix 500 PID? The manual includes a whole single sentence on using feed forward, and doesn't cover units as far as I can tell.
2. Is there a clean way to include a deadband for the FF to avoid jitter? In my hot water sets, the flow rate is constantly changing slightly, as flow does naturally, which causes the control valve to constantly make unnecessary slight adjustments, which increases wear. How do y'all handle it for situations like that?
Thanks!