Samson 3725 Compact Electropneumatic Valve Positioner with 4-20mA and Self-Calibrating for Control Valves
Product Overview
The Samson 3725 is a compact, self-calibrating electropneumatic positioner for pneumatic globe and rotary valves. It is a single-acting device that compares the control signal from the system with the actual valve stem position or opening angle, then sends a proportional pneumatic output to the actuator. Non-contact magnetoresistive sensing eliminates mechanical wear in the feedback path. The unit resists environmental effects and steam hammering. Three capacitive keys and an LCD with selectable reading direction make operation intuitive from any mounting position. All parameters are stored in non-volatile EEPROM for power-failure protection. Variable automatic start-up with preset parameters means only deviations from standard values need adjustment. A tight-closing function is available, and the zero point is continuously monitored.
Technical Specifications
| Parameter | Specification |
|---|---|
| Brand | Samson |
| Communication Protocol | HART (optional) |
| Input Signal | 4 to 20 mA, 2-wire unit |
| Data Interface | Wired |
| Diagnostics | Continuous zero point monitoring |
| Supply Pressure | Max. 7 bar |
| Mounting Type | Linear and Rotary actuators; Single-acting |
| Travel (Adjustable) | 3.75 to 50 mm |
| Opening Angle | 24 to 100° |
| Operating Temperature | -25 to +80°C |
| Enclosure Protection | IP 66 |
| Housing Material | PPA (polyphthalamide), UV-resistant |
| Air Connections | G 1/4 or 1/4 NPT |
| Minimum Current | 3.8 mA |
| Load Impedance | Max. 6.3 V (315 Ω at 20 mA) |
| Characteristic Curves | 3 travel curves, 9 rotary angle curves |
| Explosion Protection | Type 3725-000: Without; Type 3725-110: ATEX; Type 3725-113: GOST; Type 3725-130: CSA |
| Certifications | Shipbuilding certificate |
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
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Positioner does not respond to input signal: Check supply pressure (max. 7 bar). Verify pneumatic connections are secure.
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Valve position does not match input signal: Check the characteristic curve setting. Verify that the operating direction is correctly set. Recalibrate the zero point.
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Erratic operation or oscillation: Inspect for air leaks in tubing and fittings. Check for excessive friction in valve packing or actuator.
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Zero point calibration error: The zero point is out of range. Check mounting and re-adjust the zero point.
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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.
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