jeffblichmann
Member
I had an issue with my PID control in a PLC5 today. I'm using it to keep the humidity above a certain setpoint I have the input card set up to a raw min of 0 and a raw max of 100 (the block transfer read). In the PID configuration, engineering units are 0-4095, input range is 0-100. The block transfer write of the output module is 0-4095.
We recently lost power to the PLC. When power came back on, we found the PID wasn't controlling correctly, even though the process variable was below the setpoint according to the panelview.
When I went online, I found the input to the PID was 19% as expected. But opening up the PID dialog box, the process variable in the status window said 798 (about 19% of 4095). I then went to the input max/min of the PID dialog box. I changed the max to 4095, then back to 100, and then the process variable changed back to 19 as it should have been.
Any ideas why the dialog box would have shown 798 when it was actually 19? And why changing the settings then changing them back would reset that? How could I avoid this happening again?
Thank you.
We recently lost power to the PLC. When power came back on, we found the PID wasn't controlling correctly, even though the process variable was below the setpoint according to the panelview.
When I went online, I found the input to the PID was 19% as expected. But opening up the PID dialog box, the process variable in the status window said 798 (about 19% of 4095). I then went to the input max/min of the PID dialog box. I changed the max to 4095, then back to 100, and then the process variable changed back to 19 as it should have been.
Any ideas why the dialog box would have shown 798 when it was actually 19? And why changing the settings then changing them back would reset that? How could I avoid this happening again?
Thank you.