What is the low selection in an instrument control system?
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For example, a main controller X controls valves A and B in a proportional manner: 0-50% controls valve A, and 50-100% controls valve B. Low-selective control with controller Y is possible only when the controller’s output is greater than 50%. It’s my first time encountering this; could some expert please explain it to me in detail?
The selection control system and the split-range control system are two unrelated control schemes.
Split routing and low selection are two different things. I suggest you take a look at the split-curve, with the horizontal axis representing the output of the PID controller and the vertical axis representing the valve opening degree.
This is split-control: one controller controls two actuators. Which action is performed by A\B, when in automatic mode, is determined by the OP value of the controller. Low-level selection involves two or more controllers controlling one actuator.