Automatically Decel a 700H vfd with pressure setting

[remullis]

I have a need to temporarily decel a pump vfd when the head pressure reaches a certain psi. The application is pumping a slurry through sprayers that clog from time to time. Any pressure over 525 psi blows the pump diaphragm.

We monitor this pressure in logic so I know I could cut the pump off at this pressure however I need to pump to continue at a lower speed until we unplug the sprayers. Can this be done using the .spdcmd of the vfd and if so how would I go about programming this in logix.

The drive is a 700h with rslogix 5000.

 

[Peter Nachtwey]

Use two PIDs with a low select

One is the speed PID and the other the pressure PID. The pressure PID tried to control to the pressure limit. Use the minimum of the two control outputs.