I understand setpoint tracking.

But what is the difference between:

1) Having a loop in Auto and changing the setpoint from a low SP to a high SP in one step(in reference to the complete range)

vs.

2) Setting the loop mode to manual, reducing the output (affectively a low SP), then switching to Auto (already with a high SP) without setpoint tracking?

Seems to me the affect of the controller would be the same. (We are using a hybrid DCS). In one example, when we leave it in Auto, the controller has no problem with the transition between a low and high SP. Our concern is: If the operator puts it in Manual (with setpoint tracking), lowers the output (low SP) and switched back to Auto, he may forget to change the SP back to the original value.

DGR

 

Look Your Question seems that this a problem of realising a System. Whether it is Auto or Manual the SET POINT is more inportant

a) In Auto Mode Ususally Set Point realates to the Process value to be attained; So OutPut for a Supose Controlled Valve is not So important.

b) But In manual Mode Usually we are giving a direct OutPut to a controlled Valve to atain a desired Level of Process Value.

So for Yours Process Operators Do make them Responsible for Set Points and actual Process Value not just the Auto / Manual Conditions.

 

In DCS systems, mode changes are (usually) bumpless. This means that switching from manual to auto (as mentioned in your question) will result in a different controller action than when changing the setpoint value in the auto mode. Changing the SP in auto will give direct proportional and Integral controller action (PV derivative mode). Changing the mode without PV tracking (SP tracking) only the integral controller action will take care of the error (same as controller in PV proportional and derivative mode).

I have just tested it on our Yokogawa DCS and the results are inline with the above.

Regards,

Vincent
Process Automation & Control engineer

 

Hello DGR

Setpoint should track the measurement, switchover would be always bumpless.

JARI
[email protected]

 

Thank you Vincent. Your answer was exactly what I was looking for!

David