Regulation and interconnection of control valves
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I would like to ask experts in instrument control: For an existing distillation tower, the temperature at the bottom of the tower is controlled by adjusting the opening degree of the heating steam control valve (0%–100%); when the temperature becomes too high, the steam control valve is automatically shut off； At the same time, the steam control valve should be shut off when there is no water pressure (or no flow) in the condensate water, and it should also be shut off when the pressure at the top of the tower exceeds the specified level. Can a single steam control valve meet all the above requirements?
If the interlock signal is ‘1’, logic ‘or’ can be used. If the interlock signal is ‘0’, logic ‘and’ can be used.
Aren’t these just the three “or” conditions in a chain? Chain interruption can occur as long as any one of the conditions is met.
It is easy to meet the control requirements by using a DCS system. Define three 2-byte (half-precision floating-point) variables: the variable for excessively high temperature, T**LSV; the variable for excessively low condensate pressure, P**LSV; and the variable for excessively high top pressure, P**HSV. In the control program, these variables are compared with their corresponding measured values, and the results of these comparisons are fed to the EN terminal of the assignment module – as long as any one of these conditions is met. The input terminal of this assignment module is set to “0”, and the output of this module is then sent to the “MV” output of the steam regulation single-loop module, thereby fulfilling the aforementioned interlock requirements.
Thank you all for your guidance and explanations :)