FOXBORO Positioner SRD960 Series - BHNDMN6BDZNC-X1

The FOXBORO SRD960 operates on an electro-pneumatic principle to control pneumatic valve actuators, using an incoming analog signal (e.g., 4-20 mA) with HART communication to precisely position the valve. It features an intelligent self-calibration process that automatically determines the valve's geometric data and control parameters for optimized performance after installation. The positioner then uses this information to convert the control signal into a precise pneumatic output to move the actuator.

Working principle details

1. Input and feedback: The positioner receives an electrical control signal (e.g., 4-20 mA) from a control system. A position sensor within the device continuously monitors the actual position of the valve.
2. Comparison and control: The SRD960 compares the setpoint signal from the control system with the actual valve position from the sensor.
3. Pneumatic output: Based on the difference between the two signals, it sends an electrical signal to an I/P converter (if applicable), which then controls the pneumatic output pressure to the actuator. This pneumatic pressure is what physically moves the valve to the desired position.
4. Auto-start: The device can perform an "autostart" to automatically calibrate itself by finding the valve's fully open and fully closed positions, setting control parameters, and storing them for optimal operation.

  Intelligent features

• Diagnostics: The SRD960 performs self-diagnostics and provides status and diagnostic messages that can be viewed through the device's DTM software (VALcare).
• Partial Stroke Test (PST): It can perform a Partial Stroke Test to check the operability of emergency shutdown (ESD) valves, which are prone to getting stuck.

Communication:In addition to the analog signal, it supports digital communication protocols such as HART and FOUNDATION Fieldbus for configuration, operation, and diagnostics. It also has an infrared interface for wireless configuration.

Working principle: A step-by-step breakdown

1. Input and setpoint: The SRD960 receives a setpoint signal, typically a standard 4–20 mA current from a control system like a Distributed Control System (DCS). For digital communication protocols like HART, PROFIBUS-PA, and FOUNDATION Fieldbus, the setpoint is communicated digitally over the same wires.
2. Electronic control and conversion

• The positioner's internal electronics convert the incoming electrical setpoint signal into an internal reference value.
• If using HART communication, the electronic signal carries both the 4–20 mA analog control signal and a digital communications signal.

3. Position measurement and feedback

• A feedback lever on the SRD960 is mechanically connected to the valve's stem or shaft.
• As the valve moves, the lever's position is detected by an internal potentiometer or sensor. This provides a real-time electrical signal representing the actual position of the valve.

4. Error detection and control

• A digital controller within the SRD960 acts as the "brain." It constantly compares the electrical signal representing the actual valve position with the setpoint's reference value.
• If there is a difference (an error), the controller determines how much air pressure needs to be adjusted to correct it.

5. Electro-pneumatic conversion

• The controller sends a signal to the electro-pneumatic converter, which modulates the supply air. In older designs, this was often an I/P (current-to-pressure) converter. The SRD960 uses a high-performance spool valve or diaphragm amplifier for this purpose, depending on the model.
• This converter takes a constant, high-pressure instrument air supply and translates the electronic correction signal into a variable pneumatic output pressure.

6. Pneumatic output and actuation

• The variable pneumatic output pressure from the converter is fed to the valve actuator.
• For single-acting actuators, the positioner sends pressure to one side to drive the valve open or closed, with a spring providing the opposing force.
• For double-acting actuators, the positioner directs pressure to one side while venting pressure from the other to precisely control movement in both directions.

7. Closed-loop feedback

• The change in air pressure causes the valve actuator to move, changing the valve's position.
• This new position is measured by the feedback lever and sent back to the digital controller, completing the control loop. The process repeats continuously to keep the actual valve position aligned with the desired setpoint.

Intelligent features

The "intelligent" aspect of the SRD960 adds extra layers of functionality beyond basic positioning.

• Autostart with self-calibration: A key feature that automatically detects the actuator's characteristics, such as end positions and travel range, and optimizes its control parameters.
• Self-diagnostics: The positioner continuously monitors its own internal health and can display status and diagnostic messages on its local LCD screen.
• Advanced diagnostics: Using software like VALcare, the SRD960 can provide predictive maintenance features, including analyzing stroke data, monitoring friction, detecting air leakage, and generating valve health reports.
• Partial stroke testing (PST): For safety-critical emergency shutdown (ESD) valves, the SRD960 can perform a PST to periodically check for proper function without disrupting the process.
• Digital communication: Support for fieldbus protocols like HART, FOUNDATION Fieldbus, and PROFIBUS-PA allows for remote configuration, calibration, and access to diagnostic data from a control system.

 Full Datasheet

Positioner Transmitter Feature  

• Manufacturer: SRD960
• Product No. :  BHNDMN6BDZNC-X1
• SRD960 - Universal Positioner
• Version: B - Single Acting
• Input/Communication: H - HART Communication (4 - 20 mA)
• Additional Inputs/Outputs: N - Without Additional Inputs / Outputs
• Display / Indication: D - Grafical LCD (cover with window and with external pushbuttons)
• Gauges: M- Built-In Gauges with scale in bar/psi
• Pneumatical Connection: N - 1/4 - 18 NPT
• Electrical Connection: 6-  1/2 - 14 NPT (w/o cable glands or plugs for certified SRD960)
• Electrical Certification / Explosion protection: BDZ - GOST Approved For Explosion-proof
• Mounting Preparation on Positioner: N - NAMUR acc. to IEC 534-6 / Direct Mounting to Flowserve actuators
  FlowPak and FlowTop / / Rotary Actuators according to VDI/VDE 3845
• Language: C - LCD Language in English / German / Portuguese
• Booster Relay (mounted independent from positioner, for SRD960, SRD991 und SRI990, with connection G1/4): X1 - for Version single acting

There are several Model of positioner, for more details read the PDF below 

Basic Ordering Information