Step control
Thread Content
How is the valve position calculated in split-range control?
Step control involves two control valves and has four variations; only examples can be provided. Both are pneumatic on/off control valves, with the split point set at 50% of the control circuit output; 0-50% triggers valve A to operate, while >50-100% triggers valve B to operate. If the output of the control loop is 25%, what are the valve positions of control valves A/B respectively? The control loop outputs 25% within the operating range of control valve A; for control valve A, this 25% corresponds to 50% of the total output. As for control valve B, since it is not within its operating range, the valve opening degree is 0.
How to switch proportional control to automatic control,
This is already set during the instrument configuration process. For example, in the case of controlling the pressure at the top of the catalytic stabilizer, there are two control valves: one for the heat bypass and another for the non-condensable gases. If the pressure exceeds the set value, the heat bypass valve is first reduced in size; if the pressure remains high even after the heat bypass valve is fully closed, then the non-condensable gases valve is opened wider