Series 3725Electropneumatic Positioner Type 3725ApplicationSingle-acting positioner for attachment to pneumatic globe and rotary valves.Self-calibrating,automatic adaptation to valve and actuator.Reference variable 4 to 20 mA Travels 3.75 to 50 mm Opening angles 24 to 100°The positioner ensures a predetermined assignment of the valve stem position (controlled variable x)to the electric input signal (reference variable w).It compares the control signal received from a controller to the travel or opening angle of the control valve and issues a corresponding output signal pressure (output variable y).Special features•Simple direct attachment to SAMSON Type 3277Actuator (120 to 700 cm², Fig. 1)•Attachment according to NAMUR (IEC 60534-6-1)•Attachment to rotary actuators according to VDI/VDE 3845(Fig. 3)•Attachment to SAMSON Type 3372Actuator from the V2001 valve series (Fig. 2)•Easy operation with intuitive navigation menu using three ca-pacitive keys•LCD easy to read in any mounting position due to selectable reading direction•Variable, automatic start-up•Preset parameters –only values deviating from the standard need to be adjusted•All parameters saved in EEPROM (protection against power failure)•Two-wire system with a small electrical load of 300W •Tight-closing function can be activated •Continuous monitoring of zero point •Non-contact position sensing•Unaffected by environmental effects and steam hammeringVersion–Type 3725·Electropneumatic postioner with local opera-tion and LCDAssociated Information Sheet T 8350EN Edition December 2011Data SheetT 8394 ENFig.1Type 3725,direct attach-ment to Type 3277Pneumatic ActuatorFig.3Type 3725,attachment to rotary actuator according to VDI/VDE3845Fig.2Type 3725,attachment to Type 3372ActuatorPrinciple of operationThe electropneumatic positioner is mounted on pneumatic con-trol valves.It is used to assign the valve stem position(controlled variable x)to the input signal(reference variable w).The input signal received from a control system is compared to the travel or opening angle of the control valve and an output signal pres-sure (output variable y) is produced.The positioner consists of an anisotropic magnetoresistive (AMR)sensor(2),an analog i/p converter(6)with a down-stream booster(7)and the electronics unit with microcontroller (4).The travel or opening angle is measured by the pick-up lever connected to a magnet and an AMR sensor installed in the hous-ing.The motion of the pick-up lever causes the direction of the magnetic field to change.This change is sensed by the AMR sensor.The microprocessor determines the momentary valve position from this information.When a deviation occurs,the actuator is pressurized or vented. If required,the changes in the signal pressure can be slowed down by a volume restriction.The i/p module(6)is supplied with a constant upstream pressu-re by the pressure regulator(8)to make it independent of the supply air pressure.OperationA user-friendly,intuitive concept using three capacitive keys and a LCD has been developed:Users select parameters by touching the arrow keys and confirm the settings with the confir-mation key.In the menu,all parameters are listed in one level, meaning there is no need to search through submenus.All pa-rameter settings can be read and changed on site.All values are displayed on the LCD.The reading direction of the LCD can be rotated by 180°.2T8394ENTable 1·Technical data3T8394ENPositioner attachmentThe Type 3725Electropneumatic Positioner can be attached di-rectly to the Type 3277 Actuator over a connection block.When attached to the Type 3277-5Actuator (120cm²),the sig-nal pressure is routed over an internal bore in the actuator yoke to the actuator.In actuators with fail-safe action “Actuator stem retracts”and in actuators with effective diaphragm areas of 240cm²or larger,the signal pressure is routed to the actuator over ready-made external piping.Ordering textType 3725 Positioner–Without pneumatic connecting rail (only for direct attachment to Type 3277 Actuator)–Direct attachment to Type 3277 Actuator (120 to 700 cm²)–Attachment according to IEC 60534-6-1 (NAMUR)–Attachment to rotary actuators acc. to VDI/VDE 3845–Attachment to Type 3278 Rotary Actuator (160/320 cm²)–With pneumatic connecting rail G ¼–With pneumatic connecting rail ¼ NPT–Without/with pressure gauge up to max. 6 barT 8394ENSAMSON AG ·MESS- UND REGELTECHNIKWeismüllerstraße 3·60314 Frankfurt am Main · Germany Phone: +49 69 4009-0·Fax: +49 69 4009-1507Internet:http://www.samson.de2012-02Summary of explosion protection certificates (issued)Article codeII 2G Ex ia IIC T4according to ATEX11。