Principles and operation of intelligent valve positioners

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Hi everyone, your industrial control assistant is here! Today we’re sharing some knowledge about intelligent valve positioners. An intelligent valve positioner is a type of valve positioner that utilizes the HART communication protocol; it consists of three components: a microprocessor-based electronic control module, which includes a HART communication module as well as an on-site user interface switch； Piezoelectric valve of the electric/pneumatic converter module ； Valve position sensor. The working principle of the intelligent valve positioner: the entire control circuit is controlled by a two-wire, 4–20mA signal. The HART module sends and receives digital information superimposed on the 4–20mA signal, enabling two-way digital communication with microprocessors. The 4–20mA analog signal is sent to the microprocessor, where it is compared with the feedback from the valve position sensor. The microprocessor performs control calculations based on the magnitude and direction of the deviation (primary control), and sends electrical commands to the piezoelectric valve to make it open or close. The piezoelectric valve adjusts the output pressure in accordance with the width of the control command pulse, which corresponds to the increase in pressure generated by the pneumatic amplifier. The output from the pneumatic amplifier is then fed back into the internal control loop, where it is compared again with the results calculated by the microprocessor (secondary control). The output signal from this two-stage control mechanism is sent to the actuator, and changes in the air pressure within the actuator control the movement of the valve. When the control deviation is large, the piezoelectric valve emits wide-width pulse signals, causing the actuator to output a continuous signal that results in a significant change in the signal pressure applied to the actuator, thereby driving the valve to move rapidly. As the valve approaches the desired position, the difference between the commanded position and the actual measured position decreases; in this case, the piezoelectric valve emits pulses with a smaller width, resulting in intermittent and minor changes in the signal pressure applied to the actuator, which allows the actuator to move toward the new commanded position more gradually. When the valve reaches the desired position (entering the dead zone), the piezoelectric valve produces no pulse output, and the output of the positioner remains at zero, keeping the valve stable in that position. Simple Operation Guide for Intelligent Valve Positioners
Preparation:
1. Connect PS2 to the valve according to the operating instructions.
2. Check and confirm the connections of the electrical and pneumatic circuits.
3. Power it on (powered by 4–20mA current).
4. Voltage power supply is not allowed.

Initialization:
1. Confirm the feedback angles (33° and 90°).
2. Adjust the zero point and range of PS2 using the adjustment wheel and the length of the feedback rod (adjusting the adjustment wheel corresponds to adjusting the zero point, while adjusting the length of the feedback rod corresponds to adjusting the range).
3. Set the lower limit of the range to 5%–10%.
4. Set the upper limit of the range to below 95%.
5. Confirm that the valve position is at 50%.
6. Enter parameter settings and confirm the relevant parameters (Parameters 1, 2, 3).
7. Go to Parameter 4 to start automatic initialization (if manual initialization is used, go to Parameter 5).

That’s all for today’s quick tips. Updates will be provided regularly, so feel free to stay tuned.