Unformatted text preview: In-Class Problem 1 = Chapters 8,9 SEM2
The control system shown below is designed to maintain a desired internal pressure in the tank shown
( Pgas = 50 psiG). Assume the pneumatic signals shown into and out of the controller are in the range of
3-15 psig. For clarity here we use “psiG” for process gas pressure and “psig” for pneumatic control
The direct-acting pressure transmitter, PT25, has an input range of 0 to 120 psiG for measured values of
Pgas and an output of 3 to 15 psig. The pneumatic controller, PC25, is a proportional-only controller.
Its bias value , p , is set at 9 psig for the desired set point (nominal steady state) of Pgas = 50 psiG.
If the pressure in the tank increases to 100 psiG,
the valve (which is air-to-open, A-O)
should be forced to it's "fully open" condition by the controller. (a) Determine the gain of
the transmitter PT25: Km = (psig/psiG) (b) Determine the correct action of the controller and circle one choice: (1) Reverse Action or (2) Direct Action (c) Complete the table of variables (corresponding to Fig. 11.8, pg264, SEM2) and calculate the
required value for Kc. Nominal Steady State
Full var. y=50 psiG ym= Deviation y' = 0 ym' = 0 ysp=50 psiG y sp = psig e=0 p = 9 psig ysp'= 0 psig y ' sp = 0 psig e' = e p' = 0 psig "Design Condition" (Steady State)
Full var. y=100 psiG ym= psig ysp=50 psiG y sp = Deviation y'= ym'= psig ysp' = 0 y ' sp = 0 psig psiG psig Kc = e= psig p= e' = e psig p' = psig/psig psig In-Class Problem 2 = Chapters 8,9 SEM2
A simple temperature control loop is used to heat the feed stream from 30 oC to the desired
90 oC, as shown in Figure 10.1 from the SEM1 text book below. Signals are in the standard ranges of 420 mA and 3-15 psig. The direct-acting temperature transmitter, TT, has an input range of 40 to 120 oC.
The electronic controller, TC, is a proportional-only controller with a gain of Kc = 2. Its bias value, p ,
is set to be 8 mA at the nominal setpoint. The I/P transducer has an input range of 4-20 mA and an output
range of 3-15 psig and is direct acting. The control valve is air-to-open. (a) Determine the gain of the transmitter: Km = in units of . (b) At what temperature would the control valve be fully open ? T= o C ...
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- Winter '08
- Thermodynamics, Kc