STI Positioner FT Series - FT-FI00ASSA

The STI FT Series FasTrak positioner works on a digital-pneumatic principle, using a balanced-forces concept to accurately control a valve's position. It compares a 4-20 mA control signal from a control system (like a PLC or DCS) with the valve's actual position, which is measured by a feedback sensor. The positioner then uses an internal, high-flow pneumatic system to send air to or exhaust air from the actuator, driving the valve to the correct position.

Key operational steps

• Receiving the signal: The positioner receives an analog 4-20 mA input signal from a control system.
• Measuring actual position: A feedback mechanism, often a contactless sensor, provides the positioner with the valve's real-time position.
• Signal comparison: A digital control algorithm inside the positioner compares the command signal with the actual position to determine if the valve is in the desired position.
• Pneumatic control: Based on the comparison, the positioner uses a high-capacity internal spool valve to precisely control the flow of compressed air to either chamber of a single or double-acting actuator.
• Actuator movement: This pneumatic pressure moves the actuator's stem, which in turn moves the valve to the requested position.
• Feedback and equilibrium: As the valve moves, the feedback mechanism reports the new position, and the positioner continues to make adjustments until the command signal and actual position match.

• High flow capacity: The FT FasTrak positioner has a high flow rate, eliminating the need for external volume boosters in many applications and saving space and cost.
• Self-calibration: It can be configured through a software interface or via a self-calibration routine for easy setup.
• Advanced diagnostics: The positioner includes online and offline valve diagnostics for performance monitoring.
  Robust design: It features a rugged, IP66-rated housing suitable for harsh environments.
  HART communication: It supports HART protocol for advanced communication and configuration

The STI Positioner FT Series operates as a high-capacity, high-precision digital-pneumatic valve controller that employs a patented control algorithm in a closed-loop system to accurately position a valve or actuator.

Working Principle

The core working principle involves a comparison and control loop:

1. Input Signal Reception: The positioner receives a desired position setpoint as an electrical input signal (typically a 4-20 mA current signal) from a control system.
2. Position Feedback: A contactless position sensor continuously measures the actual position of the actuator or valve stem in real-time.
3. Error Calculation: An internal microprocessor and advanced control algorithm compare the received input signal (desired position) with the feedback signal (actual position) to determine any deviation or
4. Pneumatic Control: Based on the error calculation, the control logic adjusts the pneumatic output to the actuator. This is achieved through a high-capacity servo-valve or spool mechanism that controls the flow of compressed air into and out of the actuator chambers.
5. Actuation: The differential pressure of the air drives the actuator piston or diaphragm, moving the valve stem or a rotary mechanism.
6. Continuous Adjustment: This process forms a closed control loop. The positioner continuously monitors the actual position and makes rapid adjustments to the air pressure until the actual position matches the desired setpoint, overcoming friction and dynamic imbalances in the system.

Key Features Related to the Principle

• Digital Control Algorithm: The use of an advanced, patented control algorithm (including PID loop parameters) allows for accurate and fast control, with user-adjustable parameters for tuning the response (e.g., dead band, damping factor).
• High Flow Capacity: The positioner has a high air flow capacity (Cv=2 for the FT series), which allows for direct control of the valve and eliminates the need for external volume boosters in most applications, thereby increasing control quality and speed.
• Versatility: It can be configured for both single and double-acting actuators, using a simple internal setting.
• Self-Calibration: The device features a self-calibration function and can be configured and calibrated using a HART device or dedicated software interface

 Full Datasheet

Positioner Transmitter Feature  

• Manufacturer:  STI   
• Product No. : FT-FI00ASSA                                                                      
• FT - Fas Trak Positioner
• Execution: I- Intrinsically safe [ATEX/IECEX/CU TR/INMETRO/CCOE/NEPSI/KOSHA/CCC] [IP66]
• Exhaust port: 0 - Standard
• Feedback sensor: 0 - Standard Integrated
• Signal fail position: A - Standard (port A exhausted)
• Local Interface: S - Blind cover
• Type: S - HF High flow double/single acting CV 2,3 - Electrical ½” NPT- Pneumatic ½” NPT ½” NPT
• Housing: A - Alumium

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

Basic Ordering Information