ARCAPROÂ® positioner - Von Rohr ARCA BV

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ARCAPRO ®positionerPositionercustomized for specific tasks231A linear function between the input signal and stroke is thebest way to ensure maximum control precision. Controlvalves with pneumatic actuators, however, are subject tofriction, media pressure, and high flow forces, whichmeans that this linearity is not intrinsic in the system. Onlya positioner can eliminate positioning errors. To do so, itcompares the input signal (reference variable w) with theactual stroke (control variable x). Depending on the controldeviation (x W), the positioner uses the intake air pressure(p Z) to yield the actuating pressure (p S) for the actuator(actuating variable y). Either 0.2…1 bar, 4…20 mA ordigital signals can be used as input signals.1 Positioner mounting to IEC 534 (NAMUR)The standard mounting method to IEC 534 is based onmanufacturer-neutral mechanical interfaces with the actuatoryoke and stem. A bracket is normally used to securethe positioner, while the feedback lever comprises a leverwith a spring element. The inlet air is connected to thepositioner, while the pneumatic connection with the actuatoris realized by means of a pipe or hose.2 Direct integrated mountingThe positioner can be easily mounted on the actuator yokeby means of two screws to ensure that it is robust andprotected against vibrations. The feedback lever is locatedwithin the yoke, which offers better protection than theNAMUR mounting method. The actuating pressure is channeledfrom the positioner through the actuator yoke to theactuator without the need for additional piping, therebypreventing any leakage. The inlet air is connected directlyto the positioner.3 Integrated mounting to VDI/VDE 3847As with the NAMUR mounting method, this method usesstandardized mechanical interfaces with the actuator yokeand stem. The actuator interface, however, is also a pneumaticinterface, which means that, as with the directmounting method, the actuating pressure is channeled tothe actuator through the actuator yoke. In addition, the rearof the yoke is equipped with an interface for a solenoidvalve, which is pneumatically connected between the positionerand actuator, thereby enabling a safety shutdown ofthe unit. The inlet air is connected directly to the yoke,which means that no work needs to be carried out on thepiping if the positioner is replaced.244 ARCAPLUG ® stroke pick-upThe patented ARCAPLUG ® stroke pick-up connects thevalve stem and the stroke scanning lever. The taperedroller, which is made of wear-resistant plastic, gripsbetween two pins on the stem. The spring mechanism forthe tapered roller is self-adjusting, which means that thestroke is always detected without any zero backlash andwithout hysteresis. Even strong vibrations or heavyimpacts do not cause any wear and tear, and the spacingtolerances of the pins are optimal equalized.
The classic design:analog positioner type 824ARCAPRO ® positionerFunctional principlePositioner type 824 functions accordingto the tried-and-tested forcebalanceprinciple. The pneumatic setpointstandardized signal issued by apneumatic controller or I/p convertermodule generates a force on thediaphragm that is balanced with thespring force on the feedback shaft.The resulting difference in forcemoves the gate valve, which connectsthe actuator with the intake airor atmosphere, thereby controllingthe movement of the valve.Modular designPneumatic positioner type 824 ismodular in design and can be expandedwith a range of additionalmodules, thereby allowing it to beeasily customized for specific tasks.I/p converter moduleThe I/p converter module convertselectrical 0/4...20 mA input signalsto pneumatic standardized signalswith 0.2...1 bar for controlling thepositioner.Limit switch moduleTwo adjustable inductive switchesenable checkback signals for limitpositions to be sent to the controlsystem (e. g. as NAMUR signal).Feedback potentiometerThe feedback potentiometer generatesa message containing the actualposition for evaluation in the controlsystem.The intelligent design:ARCAPRO ® digital positioner type 827AFunctional principleARCAPRO ® is an intelligent, secondgenerationpositioner. It not onlyoffers a wider range of functions andhigher level of reliability, but also featuresan advanced online diagnosticssystem and optional maintenance display.The position of the stem is sentto a potentiometer whose outputsignal is then compared with the setpointby the microprocessor. Using aspecial control algorithm, the controlleractivates the two piezo valves,which connect the actuator with theinlet air or atmosphere.The ARCAPRO ® positioner can beoperated locally or from the controlroom.Optimized operating modesThe ARCAPRO ® positioner supportsthe following operating modes:■ Automatic or manual mode■ Initialization■ Parameterization■ DiagnosticsModular designThe ARCAPRO ® positioner is compactand modular.Additional modules increase yourrange of options:■ Analog module: Position transmitterfor signaling the actual positionas a current signal of 4...20 mA■ Binary module: Two adjustablesoftware limit switches, fault signalingswitch, binary input■ Slot initiator module: Two variableinductive limit switches, faultsignaling switch■ Contact module: Two adjustablemechanical limit switchesAutomatic commissioningThe automatic initialization functionallows you to commission the positionerquickly and easily. The parameterscan be set on the device or bymeans of HART, PROFIBUS or FoundationFieldbus communication. Thefollowing parameters can be set:■ Setpoint direction, characteristic■ Split-range mode■ Tight closing function■ Function for position and faultsignaling outputs and the binaryinputs3
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ARCAPROÂ® positioner - Von Rohr ARCA BV

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