Stationmaster said:That is: "HAND" is a completely independent circuit, separate from the PLC. You may consider including some safeties in this "independent" circuit by running "control power" through a set of contacts on the phase monitor and through a set of contacts on the low level sensor before it goes to the N.O. "HAND" switch contacts on its way to the contactor (or VFD).
Stationmaster
I have been waiting for someone else to chime in on this, but it has been bothering me all morning. The HAND should be independent, as so elequently indicated by Stationmaster.
JEldreth said:After reading the GDS it is critical to know all positions of all switches because there are a few valves that have to cycle before the pump can be started, even in the Hand position. I also need feedback to the HMI to know if it is Auto, Off or Hand so it looks like I will eat up 4 I/O for each station.
If you are requiring permissives for this pump to run in HAND, then you should have a hardwired circuit. HAND should be available for use when the PLC is out of service - therefore cannot make the determination if the pump could/should run in the first place.
If the process dictates that the pump should not be run manually, then the HAND should either be removed or substituted with JOG functionality.