Sensitivity of temperature control vs. pressure control

[DoraeS]

Hi, if I have one centrifugal compressor, and I would like to have the upstream control for the compressor speed, can anyone tell me that, is pressure transmitter or temperature transmitter more sensitive in term of response time? (the transmitters are both located on the suction scrubber of compressor)?
Thanks for everyone's input.

 

[roker]

hi,

response time of temperature is longer than pressure.

regards

 

[121202]

What is your control objective? Are you trying to control the pressure upstream of the compressor, i.e. varying the compressor speed to adjust to a variable inlet flow keeping suction pressure constant? Or do you have some other control objective?

 

[DoraeS]

Hi 121202,
My objective is to achieve the process gas dew point at say, 5 degC @ 85 barg. In order to achieve this dew point specification, I would like to have compressor upstream pressure maintained at 60 barg, but with temperature control as the master to the pressure control, i.e. I am actually giving a cascade control, which the temprature controller shall override the pressure controller set point if the gas temperature set point is not met. I am wondering if this is a good control as I feel that temperature control may not be so sensitive. Thanks.

 

[FrancisL]

What you describe ("the temprature controller shall override the pressure controller") is not truly Cascade control, if you really mean Override. In cascade the temperature controller would be continuously sending a a set point to the pressure controller- override being an on/off term imho.
But assuming you do mean continuous Cascade:
You say "temperature control as the master to the pressure control", which correctly for cascade would work if the temperature moves slower than the pressure.
However you also say "My objective is to achieve the process gas dew point"
That suggest to me humidity control. Do measure humidity itself?