Samson 3725 Self-Calibrating Electropneumatic Positioner with HART Communication and 4-20mA Input for Control Valves

Product Overview

The Samson 3725 is a compact, self-calibrating electropneumatic positioner designed for attachment to pneumatic globe and rotary valves. It is a single-acting positioner that compares the input control signal from the control system with the actual valve stem position or opening angle, then outputs a corresponding pneumatic signal to the actuator.

The unit features non-contact magnetoresistive position sensing, so there are no mechanical wearing parts in the feedback path. It is unaffected by environmental effects and steam hammering. Operation is intuitive with three capacitive keys and an LCD display that can be read in any mounting position thanks to a selectable reading direction. All parameters are stored in non-volatile EEPROM memory for power-failure protection.

The positioner offers variable automatic start-up, and preset parameters mean only values deviating from the standard need to be adjusted. A tight-closing function can be activated, and the zero point is continuously monitored.

Technical Specifications

Application Industry

The Samson 3725 is used in chemical and petrochemical processing, power generation, and general industrial automation. It is suitable for throttling service and applications where a compact design, easy operation, and ruggedness are essential. The positioner is developed for universal use on linear and rotary actuators.

Common Problems

• Positioner does not respond to input signal: Check supply pressure (max. 7 bar). Verify pneumatic connections are secure.

• Valve position does not match input signal: Check the characteristic curve setting. Verify that the operating direction is correctly set. Recalibrate the zero point.

• Erratic operation or oscillation: Inspect for air leaks in tubing and fittings. Check for excessive friction in valve packing or actuator.

• Zero point calibration error: The zero point is out of range. Check mounting and re-adjust the zero point.

• Initialization error: Check supply pressure and travel sensor connection. Verify valve is not stuck.

Replacement Models

The Samson 3725 is a compact positioner platform. The TROVIS 3730-1 is a direct replacement with HART communication and enhanced features. The Type 3724 is also available as an alternative in the same series. For cross-vendor alternatives, verify actuator mounting, travel range, and communication protocol before ordering.