Control Valve Calibration

P

Thread Starter

pd1986

Dear All,

I am New in Process control. i have a Samson steam control valve with zero and span setting in it. i am facing problem that when i set temp 100 from hmi, it goes up to 108 and then close and when return to 95 then again open. i want to reduce the tolerance to only 2 degrees. means if i set 100 degree Celsius then it will close max on 102 and again open on 98.

please help how can i calibrate the control valve positioner? please guide in deeply step by step as i am new to automation and control valve. model number Samson 4763 o/p 4-20ma proportional controller Samson 6109 input 4-20ma and output 0.2-1 bar.
 
R
I think you are misunderstanding what process control is all about, there is no direct connection between the setpoint in °C and the valve position.

To check the calibration of the valve put the controller in Manual and change the Controller Output, the valve should follow that and don't worry if there is a slight variation,

It's common to have the valve remain closed until the controller output is slightly higher than zero (say 5%) this ensures the valve is well closed at zero output.

Roy
 
A Samson 6109 is an I/P. An I/P converts a 4-20mA control signal to a pneumatic control signal. The pneumatic output typically becomes a control input signal to a pneumatic positioner.

A Samson 4763 is an electropneumatic positioner. An electromechanical positioner uses an electronic 4-20mA signal as an input demand signal and it senses the mechanical position of the valve stem. It supplies air to the actuator until the feedback from the mechanical position sensor shows that the valve is at the position required by the control signal. The manual for the positioner describes its mechanical setup.
http://www.samson.de/pdf_en/e83592en.pdf

One uses either an I/P or an electropnuematic positioner, not both.

What you did not describe is the loop controller. The controller generates the 4-20mA control signal. The controller needs to be "tuned" to provide the action that you are looking for.

Most controllers have an autotune function. Go find the controller manual and look up 'autotune' and follow the instructions.
 
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