Reset MotL start output

Hi All,

Is there a proper way to reset the start output of the MotL block when switching from manual>local? I want to prevent the fan to run right away when switching from manual>local, then back to local>manual.

My LocalSet parameter is set to 2, as I will need the MotL block to function if the local switch at the fan panel is set to remote.

Regards,

JP

Hi wantutri

You can try Feature Bit 10.  I don't know that it is exactly what you want, but that is the closest built in feature that describes what you want as far as I can tell from your description.

If that doesn't work as you like, you will have to write some CFC logic, possible rising/falling edge triggers to command the block as you want.

Maybe you are trying to emulate an HOA switch when you only have a L/R switch?

Hi RVS.wick,

Thanks for the reply. Let's say current conditions are the following:

1. Local switch at "Remote position"

2. Manual start using the faceplate

3. MotL block "Start" out parameter is set, fan will run.

In the event that I will put the local switch at "Local position", the MotL "Start out parameter" is still set. So when I put again the local switch back to "Remote position", since the "Start out parameter is still set, the fan runs again.

I'm still doing a simulation right now but I guess this is what will also happen if the inputs/outputs are connected physically.

Regards,

wantutri

Hi wantutri,

Yes local returning to remote is bumpless by design.  If you stopped the motor in the field while still in local (or in your simulation removed the running input) then your command output will stop.  If you don't remove the running feedback prior to switching out of local, the motor keeps running, unless you return to auto instead of manual, then it will follow the auto command.

It sounds like instead of simple local/remote you desire Hand/Off/Auto control in one direction only, where the motor has to pass through Off when returning to DCS control.  Typically this functionality is done electrically in the motor starter, but in your case you have to make it yourself in code.

So you will have to write some CFC logic.  There are many ways to do this depending on your preference and exact use case when combined with your other logic in your CFC or CMT.  I suggest using some triggers and potentially flip flops on local/remote signal and AND/OR logic with the running feedback to command the motor to stop in local upon exiting.

I faced the same issues two years ago, and my solution was ...customized my own PTT for the motor template. 

Check and test as much as you can to Fix the operation of the motor. The most important is the Auto/Manual/Local/Remote. From Auto to manual, manual to auto, auto to local, local to manual, how the pump behave. 

Show you a sample here. (which I don't really like it. But sometimes during commissioning, we have quite limited time to test)

I will have a look on your suggestions.

Many thanks!