The positioner is the main control valve accessories . Would stem displacement measurement signal input as a feedback signal to the controller output signal as setting signal , comparing the two when there is deviation , change its output actuator signal , the actuator operation to establish correspondence between the amount of displacement of the valve stem and the controller output signal. Therefore , the composition of the positioner to the valve stem displacement measurement signal to the controller output signal is set to a feedback control system. The manipulated variable is the valve control system to perform the output signal of the positioner body .
2.Action
(1) Be used to adjust the high quality requirements of important regulatory systems to improve the positioning precision and reliability of the control valve.
(2) for a large pressure difference across the valve ( p> 1MPa) occasions. Increased by increasing the air pressure actuator output force to overcome the imbalance force generated by the liquid on the spool reduces stroke errors.
(3) When the transfer medium temperature, high pressure, low temperature, toxic, flammable, explosive, in order to prevent leakage of foreign, often the very tight packing pressure, and therefore the larger the friction between stem and packing, this time Delays can be overcome with a locator.
(4) the medium was adjusted to contain the viscous fluid or suspended solids, can be overcome by positioning the media resistance to movement of the valve stem.
(5) for large diameter (Dg> 100mm) of the control valve to increase the output thrust of the actuator.
(6) When the actuator when the actuator 60m from above, can be overcome by positioning the hysteresis control signal is transmitted, the operation of the valve to improve the reaction rate.
(7) Be used to improve the flow characteristics of the control valve.
(8) A regulator control of the two actuators to implement process control, the two positioning devices can be used to receive either a low input signal and the input signal is high, the lower the forward movement of an actuator, other elevation movement, constitutes a sub-Cheng regulation.
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