Aim : To study level control using 1 – Element (Level) Single Loop PID.
Control System : It consists of the following in feedback.
LT11 - Level
LIC11 - Loop 1, PID 1, of LIC/FIC11
LCY11, LCV11 - Control Valve at Inflow Pipe
Special Remarks : LIC/FIC11 is in the 1 – Element position with Loop 1 in A mode.
1. Pump P13 was switched OFF as there is no necessity to operate the product flow system. The heater was also turned OFF as there is no necessity for heating.
2. A final check was done to ensure that the instrument air supply was 25 psig
(1.7 Barg), the overflow drain valve and the vent at tank T11 were opened.
Proportional (P) and Integral (I) Control were set into LIC11 (Loop 1, PID 1) using the trial values for LIC11.
PB1 = 18%
TI1 = 56secs
TD1 = 0secs
11. The level PV1 at LC11 was observed. The SV1 setpoints was moved until it is near the measurement value PV1. “A” button was pressed to switch LIC11 to Automatic Mode.
12. The recorder LFTR11 was set at fast speed (500mm/HR). The control response (red pen) of the level was observed until the response was steady. The result is as follow:
13. The SV1 setpoint was increase about 50mm and the control response of the level was observed at LFTR11 (red pen).
14. The above procedures were repeated with a different set of PID values. After each change of new PID values, the setpoint was disturbed and the level response was observed until it is steady.
PB1 = 10%
TI1 = 30secs
TD1 = 0secs.
15. Repeated with other PID values.
PB1 = 95%
TI1 = 70secs
TD1 = 0secs
16. The process was disturbed with different ways.
Setpoint step changed as above.
The by-pass valve around the inflow pump P12 was opened-closed to disturb the flow.
The outflow was increased by opening the “Other Demand” valve.
LIC11 was put in Manual (M) mode and its control output was manually step change to LCV11 by 10%.
LIC11 was quickly put back into Automatic (A) mode.
17. The vent and overflow drain valve at the top of tank TI1 were shut. The top space of tank T11 was pressurized by opening the air supply valve between TI1 and the regulator AR1, to a few psig. Any difference to the level measurement was observed at LT11. The vent and overflow drain valve...