Article Details
Valve positioners are divided into pneumatic valve positioners, electro-pneumatic valve positioners and intelligent valve positioners according to input signals. The input signal of the pneumatic valve positioner is a standard gas signal, for example, 20~100kPa gas signal, and its output signal is also a standard gas signal. The input signal of the electric valve positioner is a standard current or voltage signal, for example, a 4~20mA current signal or a 1~5V voltage signal, etc. The electric signal is converted into an electromagnetic force inside the electric valve positioner, and then the gas signal is output to the toggle control valve. The intelligent electrical valve positioner converts the current signal output by the control room into the gas signal that drives the regulating valve. According to the friction of the valve stem when the regulating valve is working, it offsets the unbalanced force caused by the fluctuation of medium pressure, so that the valve opening corresponds to the current signal output by the control room. It can also perform intelligent configuration to set corresponding parameters to achieve the purpose of improving the performance of the control valve.
According to the direction of action, it can be divided into one-way valve positioner and two-way valve positioner. When a one-way valve positioner is used in a piston actuator, the valve positioner only works in one direction. A two-way valve positioner works on both sides of the cylinder of the piston actuator and works in both directions.
According to the gain sign of the valve positioner output and input signals, it is divided into direct acting valve positioner and reaction 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 to a reaction valve positioner increases, the output signal decreases and, therefore, the gain is negative.
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 fieldbus electrical valve positioner. The input signal of an ordinary valve positioner is an analog air pressure or current or voltage signal, while the input signal of a fieldbus electrical valve positioner is a digital signal of the fieldbus.
Depending on whether the valve positioner has a CPU, it can be divided into ordinary electrical valve positioners and intelligent electrical valve positioners. Ordinary electric valve positioners do not have a CPU, so they do not have intelligence and cannot process related intelligent operations. The intelligent electrical valve positioner is equipped with a CPU, which can handle relevant intelligent operations, such as nonlinear compensation of the forward channel, etc. The fieldbus electrical valve positioner can also be equipped with PID and other functional modules to implement corresponding operations.
It can also be classified according to the detection method of the feedback signal.
For example, a valve positioner that uses a mechanical connecting rod to detect the valve position signal; a valve positioner that uses the Hall effect to detect the displacement to detect the valve stem displacement; a valve positioner that uses electromagnetic induction to detect the valve stem displacement, etc.
