With out the rest of the system or process it would only be a guess.
A plc will do what you tell it to. So you must have inputs to tell the PLC
what is happening. The you write a program to do your process. Then you will
connect to the outputs to get the valve to open and close. There are
different kinds of inputs and outputs analog which is scaleable and digital
which is open and closed. Be glad to help need more information
My problem is that i don't know exactly how a motor driven butterfly
I suppose there is a DC motor to turn the valve. I suppose you have to
put an encoder in the shaft to know the position of the valve, and from
the PLC you order the motor to stop or to run. However, how do you know
the number of revolutions the motor must run from a wide open position
to a close one?
As I said, it's the valve+motor, not the PLC, what I don't understand.
MOV (Motor Operated Valves) come in all sizes and shapes. Usually a
butterfly valve is *not* meant for throttling/process control (their flow
characteristic is very non-linear). For process control, typically a form
of globe valve with specially designed 'trim' is usually called for (the
'trim' may be linear, 'equal-percentage', or 'quick-opening' depending on
In many industrial cases, the operator is a gear train with an auxilary
shaft that turns as the valve itself is moved. Various schemes of limit
switches are arranged on the auxilary shaft to stop the motor at the full
open and full closed positions. A reversible AC motor drives the whole
scheme with a couple of contactors ('42' devices) and motor overloads. PLC
not really necessary unless just to replace the manual control switch
contacts to initiate opening or closing.
If you *do* want to stop/control the valve in some intermediate position,
you would need a position signal. RVDT (rotory variable differential
transformer) or LVDT (linear variable differential transformer) are common,
but so is plain and simple potentiometers.
On 8/20/04 12:00 PM, in article email@example.com,
A set up like you describe is used on a flow control for agricultural
sprayers. The ones I saw operated on 12VDC. This application has the
motor directly turning the valve with no gear reduction. A flow meter tells
the controller to open or close the valve to regulate flow. It does not
completely stop the flow. This valve is just a flap inside the valve. It
looks like a choke inside a carburetor. Hiniker is one brand.
A ball valve was used once on irrigation systems to shut off water for the
end sprinkler. It was 120 VAC. That had gear reduction. A couple of cams
mounted directly on the valve shaft tripped a couple of micro switches. The
switches would tell the motor to stop turning when the valve reached the
fully closed or open position. Jamesbury is one brand.
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