RSLogix 5000 PID - Tieback / Manual

[slick_william]

Hello everybody, been a longtime viewer of the forum, this is my first time posting. Nice to meet you all.

I am working with a system which uses a PID instruction to control a VFD speed to deliver a desired flow rate, easy peazy. Additionally, the operator wants to be able to switch into a mode (via an HMI) which would then run the VFD at a manual speed setpoint.

For example, say the operator runs the pump to deliver 250 gpm of flow, so the PID takes over and we end up with a final VFD speed of something random, say 55.4 %.

Then the operator goes "okay, I want to run my VFD at 70% speed now". He/she hits a button on the HMI, and now 70% speed command gets sent directly to the analog output which controls the VFD speed.

So after a few hours of research, I think the tieback parameter inside the PID instruction (along with the manual control bit--.CTL.24) might be able to accomplish this.

Is it possible to accomplish this type of control using the PID block by itself, along with the tieback SP and manual function? Or will I need to add additional programming to handle the manual speed control?

If anyone could answer that, I can handle the rest.

Thanks all

- Will

 

[janner_10]

If you want to set a manual output on the PID:

Set MyPid.SWM to true and write the output value to MyPid.SO

(.SWM is software manual and .SO is set output)

 

[slick_william]

janner thank you for the answer. I will give that a try.

Have a blessed day

 

[rupej]

That's all there is to it. And setting the .swm bit to false will automatically result in a bumpless transfer from where the PID was when in manual.