Hello,
One year experience here. Nice to find good forum with DeltaV community.
I have pressure control loop with AI, PID, and AO that controls between 0-10 psig fine. The control strategy is that with increaseing pressure, the PID out increasing (0-100%) opening the valve.
I want to re-range the pressure transmitter to read higher pressure values between -5 to 60 psig, however I would like still control between 0-10psig only.
1. Currently my AI Out_Scale is 0-10psig and PV_Scale of PID block is 0-10 psig. Do I need to change the AI Out_Scale to -5-60 psig after and leave the PID PV_Scale at 0 - 10 psig after reranging the transmitter in filed?
2. What happens if I rerange my transmitter to -5-60 psig, change AI OUT_Scale to -5 to 60 psig, and change PID PID PV_Scale to -5 to 60 psig, but my process operating range remains between 0-10psig? I am thinking the valve will slightly open at 10psig.
Thanks all for your support and help
The ranges specified do not really affect the performance of the control, but consider that if you have re-ranged your meter and you expect to see process variables outside of your current range, then tuning of your loop may need to be revisited. You may even need to employ non-linear tuning parameters if you operate between 0-10 99% of the time and want a different tuning for the rare occassion you are out of this range.
I would make the scales consistent throughout the loop, however, for clarity, and to avoid over/underranging in one part of your loop versus another.
Hi Darrell.
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In reply to Youssef.El-Bahtimy:
Thank you Youssef,
Yes, I was confused thinking if I re-range the meter that this will effect the control of the loop. When actually, i can set th SP_HI_LIM as 10 and SP_LO_LIM as 0 and my control loop will only be allowed to control between these two loops as original design. My control valve is designed to control with this range, so no problems here.
My process conditions will stay the same as before and still require control between 0-10psig. However, there for re-ranging the meter to measure higher pressures is needed for data historian collection for those rare cases of overpressure.
Let me know if my thinking is correct.
Thanks
In reply to Rachelle McWright:
Thank you Rachelle.
Nice to be here. Hopefully my knowledge can help others.
Thank you Rachelle. I am happy to be here. Hopefully my knowledge can help others.
In reply to DCS Newbie:
Changing the SP Hi and Lo limits is a good strategy. Update the PV_SCALE and OUT_SCALEs on the AI and PID to reflect the true nature of the process measurement. Doing so will also ensure any faceplates designed for the loop have consistent information as well. Don't forget to adjust alarms setpoints.
Thank you Youssef, i was able to do as you mention with no problem. Thank you
Good to know. Keep the discussions coming. Thanks.