Emerson Exchange 365

In reply to LaurentB:

I don't know if I understood correctly, but you can try with i deadband = 3.
The reset will be limited on both sides and your process will be more stable.

In reply to laurent maurer:

No KNL is different than Ideadband
the initial request is PID_OUT (MV) will only action when PV deviate below setpoint, say -3DegC below SP => with KNL you can get exactly this.
With ideadband with a small disturbance <3°C you can have a PID_OUT move ( especially if the GAIN is high)

I agree that with Ideadband temperature control will be more stable, but maintening an accurate temperature can introduce up or downtsream disturbance and control valve can have oscillation to a lower lifecycle.

In the case of temperature can move on the +-3°C around the setpoint without quality issue, it's better to think KNL. KNL is especially used on level control but can be applied when a tight control is not required by quality or safety reasons

I'll explain that to you the next time we meet us ;-)

In reply to LaurentB:

I agree with your explanation but the i deadband is easy to set up and understand.
But i will check KNL in the book online.

;-)

Hi Robin,
you might give us some more information about your setup.
Is your Control Valve a single one, not split-range.
Why do you want act only if PV ist too cold and then only more than 3DegC?
Did you checkout the PID/Processtype parameter?
(self control or integrating)
Do you have an exotherm process?
You want to keep the actual PidOut and only if PV is 3DegC less than SP want to change your control valve.
A simple option where to play with the OUT_HI/LO_Lim, controlled by a calc block at you predefined rules.
You might freeze the OUT with OUT_HI_LIM if you are in a SP deathband and release OUT_HI_LIM slowly to 100% to get more heating. Check also the ARW_HI_LIM
What shall happen if the PV become too warm?