PID Loop reaction to loss of power

[JoshM]

Hi Guys,

I have a scenario where when control power is lost to my PLC, PID's that were running retain their previous output, but PID's that weren't controlling and just had states being written to their outputs zeroed out. Does this make sense? Is there a way to make those PID's loop go to a preferred known state?

I am using relogix5000 to code.

Regards,

JoshM

 

[mellis]

Without seeing your code, hard to say what is going on.

All memory is retentive in AB PLCs. So it's either a pre-scan action, or your code that is doing it.

 

[Ron Beaufort]

if I remember correctly, your system is using PIDE - not PID ... the rules for prescan action are quite a bit different ...

the Instruction Help for PIDE has a lot to say about how "start up" will affect the system's operation (it's close to the end of a long description) ... but ... there's a LOT involved depending on how the system is configured ...

suggestion:

post your code - and tell us WHAT you want each PID or PIDE to do in a "start up" condition ... we can probably make it happen - but we need to know specifically what operation you desire ...

 

[JoshM]

Thanks guys.

The main difference I'm seeing is that the PIDE loop that zeros has a CVHAlarm and Winduplout alarm. When alarms are active on a PIDE does it reinitialize where none alarmed PIDE's just continue what they were previously doing?