1. The valve positioner is divided into pneumatic valve positioner, electrical valve positioner and intelligent valve positioner according to the input signal.
(1) The input signal of the pneumatic valve positioner is a standardized gas signal, for example, the 20-100kPa gas signal, and its output signal is also a standardized gas signal. (2) The input signal of the electrical valve positioner is a standard current or voltage signal, for example, 4-20mA current signal or 1-5V voltage signal, etc., the electrical signal is converted into electromagnetic force inside the electrical 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 control valve, and counteracts the unbalanced force generated by the fluctuation of medium pressure according to the friction of the valve stem during the operation of the control valve, so that the valve opening corresponds to the current signal output by the control room. And the corresponding parameters can be set by intelligent configuration to achieve the intention of improving the function 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 in a piston actuator, the valve positioner works in only one direction, and the two-way valve positioner acts on both sides of the piston actuator cylinder and works in both directions.
3. According to the gain symbol of the output and input signal of the valve positioner, it is divided into positive acting valve positioner and reaction valve positioner. When the input signal of the 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, and as a result, the gain is negative.
4. According to the valve positioner, the input signal is an imitation signal or a digital signal, which can be divided into a general valve positioner and a fieldbus electrical valve positioner. Generally, the input signal of the valve positioner is to imitate the air pressure or current and voltage signal, and the input signal of the fieldbus electrical valve positioner is the digital signal of the fieldbus.
5. According to whether the valve positioner has a CPU, it can be divided into general electrical valve positioner and intelligent electrical valve positioner. Generally, electrical valve positioners do not have a CPU, therefore, they do not have intelligence and cannot handle the relevant intelligent calculations. The intelligent electrical valve positioner with CPU can handle relevant intelligent calculations, such as nonlinear compensation of forward channels, etc., and the fieldbus electrical valve positioner can also be equipped with PID and other functional modules to achieve corresponding calculations.
6. It can also be classified according to the detection method of the reaction signal.
For example, a valve positioner that detects a valve position signal by a mechanical linkage method, a valve positioner that detects the displacement of a valve stem by detecting the displacement using the Hall effect, and a valve positioner that detects the displacement of a valve stem by electromagnetic induction.
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