Question

Q2. The level of liquid in a vessel is controlled by pure proportional control. The controller acts on a valve on the outlet stream by means of an analogue current signal in the range 4-20 mA. The valve stem position responds linearly to the current over the range 0-100% and for this installed valve it is known that the % of max flow is roughly equal to the % stem position (c.f. course notes p34, Fig 23). The maximum flowrate through the valve is 100 m³ hr?¹. At an initial steady-state condition, the level in the tank is at its set-point and the flow rates into and out of the tank are both 50 m³ hr?¹. After a step-change disturbance in the inlet flowrate of 5 m³ hr?¹, the process response results in a steady-state offset of 50 cm in the tank level. a) Calculate the gain of the controller (in mA/m) b) How should the gain be altered to limit level changes to ±1 m when the inlet flowrate may vary between 20 and 80 m³ hr?¹.

          Q2. The level of liquid in a vessel is controlled by pure proportional control. The controller acts on a
valve on the outlet stream by means of an analogue current signal in the range 4-20 mA. The valve
stem position responds linearly to the current over the range 0-100% and for this installed valve it is
known that the % of max flow is roughly equal to the % stem position (c.f. course notes p34, Fig 23).
The maximum flowrate through the valve is 100 m³ hr?¹.
At an initial steady-state condition, the level in the tank is at its set-point and the flow rates into and
out of the tank are both 50 m³ hr?¹.
After a step-change disturbance in the inlet flowrate of 5 m³ hr?¹, the process response results in a
steady-state offset of 50 cm in the tank level.
a) Calculate the gain of the controller (in mA/m)
b) How should the gain be altered to limit level changes to ±1 m when the inlet flowrate may
vary between 20 and 80 m³ hr?¹.

Q2. The level of liquid in a vessel is controlled by pure proportional control. The controller acts on a
valve on the outlet stream by means of an analogue current signal in the range 4-20 mA. The valve
stem position responds linearly to the current over the range 0-100% and for this installed valve it is
known that the % of max flow is roughly equal to the % stem position (c.f. course notes p34, Fig 23).
The maximum flowrate through the valve is 100 m³ hr?¹.
At an initial steady-state condition, the level in the tank is at its set-point and the flow rates into and
out of the tank are both 50 m³ hr?¹.
After a step-change disturbance in the inlet flowrate of 5 m³ hr?¹, the process response results in a
steady-state offset of 50 cm in the tank level.
a) Calculate the gain of the controller (in mA/m)
b) How should the gain be altered to limit level changes to ±1 m when the inlet flowrate may
vary between 20 and 80 m³ hr?¹.

Added by Christopher L.

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