May 6, 2025
Generally divided into two categories of intelligent positioner and ordinary positioner, the so-called semi-intelligent positioner is also an intelligent positioner, only the intelligence is not complete.
Ordinary positioner only analog circuit, generally with the nozzle baffle mechanism.
Intelligent positioner for the digital circuit, can be superimposed on the Hart protocol. Internal with multi-digit digital valve, each valve is equivalent to a bit in binary. No static air consumption. Very powerful, but high requirement for gas source, such as ABB, Siemens. If the quality of your gas source is not good or the quality of field personnel is not high enough, it is not recommended.
Another kind of intelligent positioner is also a digital circuit, but still use the old nozzle baffle mechanism, we call it semi-intelligent positioner, I do not know if this is the official name. In fact, our experience, this good to use, such as Yamatake, fisher.
2. intelligent valve positioner compared with the traditional valve positioner
The traditional electric / gas valve positioner is the main control accessory of the pneumatic control valve, and the valve supporting the composition of the pneumatic control valve with electric / gas valve positioner. The signal from the regulator output after the positioner proportional amplification output to control the actuator action, when the valve stem movement, its displacement and through the mechanical device negative feedback to the valve positioner, thus constituting a valve stem displacement and input pressure proportional to the negative feedback system. The valve positioner corrects the deviation of the valve stem stroke and restores it to the corresponding relationship between the control signal and the valve stem stroke, thus ensuring the correct position of the regulating valve.
Intelligent valve positioner as a new generation of products, the traditional type of valve positioner function and digital communication technology combined, performance has a great breakthrough. For example, the control accuracy has been improved; automatic adjustment of the zero position, automatic adjustment of the full scale; intelligent valve fault diagnosis technology; maintenance and field adjustment is very convenient and so on.
3. the choice of intelligent valve positioner superiority
Through the above theoretical and engineering applications on the analysis and comparison, the choice of intelligent valve positioner may improve the performance of the control system, so that the field adjustment is more convenient.
(1) the controlled object nonlinear characteristics of the compensation method has been expanded.
Controlled object nonlinear characteristics can be compensated by the control valve flow characteristics; available ordinary valve positioner or intelligent valve positioner to compensate; also available intelligent digital controller (for example, single-loop or multi-loop controllers or DCS in a variety of digital controllers) connected to the nonlinear link to achieve. From the point of view of reducing investment costs and reduce maintenance, etc., the use of intelligent valve positioners or digital controllers connected to the nonlinear compensation link has the function of soft connection, can easily change the nonlinear characteristics and other advantages.
(2) The selection of control valves becomes simple.
Control valve flow characteristics can be all linear flow characteristics or easy to process, high precision flow characteristics, thereby reducing the type of control valve flow characteristics. If the use of sleeves and other valve parts, but also to reduce the control valve body specifications, so that the user's control valve spare parts types and specifications are greatly reduced. Sleeve valves and other control valves can also choose to balance the valve parts, noise reduction network and other components for high pressure differential and the requirement to reduce the noise of the application.
(3) Eliminate the nonlinear compensation function of the valve positioner.
Due to the nonlinear characteristics of the feedback cam affects the stable operation of the control system, the control valve flow characteristics of the compensation function can be realized by the intelligent valve positioner, therefore, the nonlinear compensation function of the valve positioner can be removed from its function.
(4) The valve positioner's valve position detection adopts a non-contact method, which can greatly improve the performance of the control loop.
(5) Intelligent valve positioner can be added to the overrun hysteresis link. Used for serial resonance to increase the sub-loop time constant, stagger the resonance frequency.
4. the actual engineering applications
In practical engineering applications, it is more likely to bring:
(1) Reduce the cost of loop commissioning, including installation costs and calibration costs;
(2) The role of intelligent diagnostic techniques to maintain the circuit, software diagnosis is the direction of development of valve fault diagnosis;
(3) Improve process control by reducing process deviation;
(4) Automatic calibration and configuration. Compared with the traditional zero and range calibration, it can significantly save time;
(5) Valve diagnosis. Through the DCS, PC software or hand manipulator, the user can make online diagnosis of the health status of the valve, do not need to disassemble the valve to detect the actual situation of the valve, so that predictive maintenance is possible;
(6) Remote communication capability. It can realize valve monitoring and report its equipment to the user.
