Foxboro SRD991 Microprocessor-based Smart Valve Positioner with HART 4-20mA and SIL 3 Capability

Product Overview

The Foxboro SRD991 is a microprocessor-based intelligent valve positioner designed to accurately control pneumatic valve actuators. It supports single-acting and double-acting actuators for both linear and rotary applications. The device offers local configuration via push-buttons and a multilingual graphical LCD, advanced self-diagnostics, and multiple communication options.

The positioner features an easy-to-operate, menu-driven graphical LCD with multilingual full-text display. All parameters can be configured locally by push buttons. A time-saving automatic startup with self-calibration gets the positioner ready for operation in just two steps. Status and diagnostic messages are displayed on the LCD.

Communication options include HART, FoxCom, PROFIBUS-PA, FOUNDATION Fieldbus H1, or no communication. The unit is SIL 3 capable and offers advanced and premium diagnostics including valve footprint, online friction, position/response history, and Partial Stroke Test (PST). Mounting follows NAMUR standards for linear actuators and VDI/VDE 3845 for rotary actuators.

Technical Specifications

Application Industry

The Foxboro SRD991 is used in petrochemicals, power generation, water treatment, paper, and general industrial process control. It is suitable for precise throttling control of pneumatic linear and rotary valve actuators in demanding environments. The SIL 3 capability and Partial Stroke Test function make it suitable for safety instrumented systems (SIS) and emergency shutdown (ESD) valves.

Common Problems

• Input signal mismatch: If the positioner's recognized input signal differs from the DCS or calibrator output, check the power supply voltage. If supply current is normal, reset the <IN ZERO> and <IN END> values in the <TUNING> menu.

• Hunting or oscillation: If hunting occurs due to high valve packing friction, increase the dead band value within the field-allowed range. If the dead band is set too low, it slows the search for the target point.

• EEPROM error: Check whether the positioner is installed too high or too low. Check if it is installed too far from the actuator (check the angle of use). Check if the potentiometer gear and main gear are out of position due to strong vibration or external shock.

• No response to input signal: Check supply pressure is within 1.4~6 bar. Verify pneumatic connections are secure. Check the feedback lever installation.

• Slow valve response: If the actuator size is too large, set the TbL value to TbL 4 (LLS). If the torque motor is damaged, replace it.

• Air leakage: Check O-rings, gaskets, and diaphragm for wear. Replace as needed.

Replacement Models

The Foxboro SRD991 is a current-generation intelligent valve positioner platform. The SRD960 and SRD998 are other models within the same product family. For applications requiring SIL 3 capability, the SRD991 is already certified. For cross-vendor alternatives, the Fisher DVC6200, Samson 3730, Siemens SIPART PS2, and Neles ND9000 are frequently cited as direct competitors.