Article Details
(1) Improve the static characteristics of the valve
After using the valve positioner, as long as the output air pressure of the regulator changes slightly, through the action of the nozzle-baffle system and the amplifier, the air pressure leading to the diaphragm head of the regulating valve can change greatly to overcome the friction of the valve stem and eliminate the influence of the unbalanced force of the regulating valve, ensuring that the valve position is correctly positioned according to the signal sent by the regulator.
(2) Improve the dynamic characteristics of the valve
The positioner changes the first-order hysteresis characteristic of the original valve, reduces the time constant, and makes it a proportional characteristic.
(3) Change the flow characteristics of the valve
By changing the shape of the positioner feedback cam, the linear, quick-opening and other percentage flow characteristics of the valve can be changed.
(4) Used for split-range control
In a general process control system, the output signal of a controller drives a control valve to perform a full-stroke action, while a split-range control system has the function of controlling multiple valves. Each control valve can only perform a full-stroke action within a certain section of the controller’s output signal. The division of the controller’s output signal section is determined according to the production process requirements. There are two purposes of split-range control: one is to expand the adjustable ratio of the control valve and improve the control quality of the system and increase the stability of the system; the other is to meet certain special requirements of process operations. For example: make two regulating valves complete full stroke movement within the signal range of (20-60kPa) and (60~100kPa) respectively.
