Ratio control of control valves
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The oxygen control valve and the hydrogen control valve mix in a 3:1 ratio as controlled by a ratio controller (the ratio module in the DCS), and then output a signal proportionally to this ratio. If the ratio exceeds a certain value (for example, becomes 3.5:1), the oxygen control valve is prevented from opening further; it can only be adjusted to a smaller opening degree. It makes sense that opening it fully is prohibited here; adding a limiting module will do the trick. But what about allowing it to be closed only? How should that be handled? Is there anyone who can solve this? Please help answer it.
This post was last edited by huio1983 on 2016-1-27 at 15:25; the operating mode of the valve was changed – if it was positive acting, it was changed to negative acting, and vice versa. Control modules generally have control interfaces for positive and negative actions
This post was last edited by huio1983 on 2016-1-27 at 15:54. If that doesn’t work, simply perform subtraction – use twice the limit value to subtract from the output of the module calculation
Cann’t ratio control be used to achieve this? The output of the ratio controller controls the oxygen control valve; when the oxygen to hydrogen ratio is greater than 3:1, the oxygen control valve is definitely closed.
The control valve is equipped with a limit mechanism; linear opening adjustment is sufficient, and the limit should be adjustable as required.
The poster is controlling the ratio; setting a limit on the oxygen valve is useless; limits can only be added through DCS configuration.