Classification of valve positioners

Valve positioners' classification

1. Valve positioners are divided into pneumatic valve positioners, electro-pneumatic valve positioners and intelligent valve positioners according to the input signal.

(1) The input signal of the pneumatic valve positioner is a standard gas signal, for example, a 20~100kPa gas signal, and its output signal is also a standard gas signal.

(2) The input signal of the electric valve positioner is a standard current or voltage signal, for example, 4~20mA current signal or 1~5V voltage signal, etc. The electric signal is converted into electromagnetic force inside the electric valve positioner, and then the gas signal is output to the toggle control valve.

(3) The intelligent electrical valve positioner converts the current signal output from the control room into the gas signal that drives the regulating valve. According to the friction force of the valve stem when the regulating valve is working, it offsets the unbalanced force generated by the fluctuation of the medium pressure and makes the valve opening. Corresponds to the current signal output from the control room. And can carry out intelligent configuration to set the corresponding parameters to achieve the purpose of improving the performance of the control valve.

2. According to the direction of action, it can be divided into one-way valve positioner and two-way valve positioner. When the one-way valve positioner is used for the piston actuator, the valve positioner only works in one direction, and the two-way valve positioner acts on both sides of the piston actuator cylinder and works in two directions.

3. According to the gain symbols of the output and input signals of the valve positioner, it is divided into a positive-acting valve positioner and a reverse-acting valve positioner. When the input signal of a positive-acting valve positioner increases, the output signal also increases, so the gain is positive. As the input signal of the reaction valve positioner increases, the output signal decreases, so the gain is negative.

4. According to whether the input signal of the valve positioner is an analog signal or a digital signal, it can be divided into ordinary valve positioner and field bus electric valve positioner. The input signal of ordinary valve positioner is analog air pressure or current, voltage signal, and the input signal of fieldbus electric valve positioner is the digital signal of fieldbus.

5. According to whether the valve positioner has a CPU, it can be divided into ordinary electric valve positioner and intelligent electric valve positioner. Ordinary electric valve positioners do not have a CPU, therefore, they do not have intelligence and cannot handle related intelligent operations. The intelligent electric valve positioner has a CPU, which can process related intelligent operations, such as nonlinear compensation of the forward channel, etc., and the fieldbus electric valve positioner can also carry functional modules such as PID to realize the corresponding operation.

6. It can also be classified according to the detection method of the feedback signal. For example, the valve positioner that detects the valve position signal by the mechanical linkage method: the valve positioner that detects the displacement of the valve stem by the method of detecting the displacement of the Hall effect: the valve positioner that detects the displacement of the valve stem by the electromagnetic induction method, etc.