STI Positioner SHP Series - SHP-TH00ADSAL

The STI SHP Positioner works on a digital force-balance principle, using an advanced control algorithm and a spool valve to precisely control a valve's position based on an input signal. It receives a control signal (like 4-20mA), compares the desired position to the actual position measured by a contactless sensor, and then uses its internal logic to adjust the air pressure to the actuator. The positioner's high-flow design and patented algorithm enable quick response times and accurate control. 

Working principle

• Digital control: Unlike older analog positioners, the SHP uses a digital system with a patented control algorithm to process the input signal and manage the actuator's movement.
• Force balance: The positioner operates on a force balance principle, constantly comparing the input signal to the position feedback from the valve stem.
• Spool valve: Air distribution to the actuator is controlled by an internal spool valve, which opens and closes supply and exhaust ports to move the actuator to the correct position.
• Feedback loop: A contactless position sensor provides real-time feedback on the valve's actual position to the control unit. The positioner compares this feedback to the desired position from the input signal.
• Smart adjustments: If there is an error between the desired and actual position, the positioner's algorithm directs the spool valve to supply or exhaust air to the actuator chambers until the error is corrected.
• Advanced diagnostics: The SHP includes online and offline diagnostic features, such as valve signature tests, to monitor performance and predict potential issues, which helps to minimize downtime.

The STI Positioner SHP Series is a digital pneumatic positioner that operates on a feedback control loop principle, using advanced control algorithms (such as PID control) to precisely position a valve.

Working Principle

The core principle involves a continuous comparison between a desired valve position (setpoint) and the actual, measured position of the valve, with the positioner adjusting the air pressure to the actuator to correct any difference (error).

1. Input Signal Processing: The SHP positioner receives an analog input setpoint signal (typically 4-20 mA) from a control system, which indicates the required position of the valve.
2. Position Feedback: The positioner uses an internal, contactless position feedback sensor (or an optional remote sensor) to measure the actual, real-time position of the valve stem or shaft.
3. Error Calculation: A microprocessor within the positioner compares the input setpoint signal with the feedback signal from the position sensor. The difference between the desired position and the actual position is the error signal.
4. Control Logic and Amplification: Advanced, patented control algorithms (based on principles like PID control theory) process the error signal. This signal is then amplified to direct the pneumatic output.
5. Pneumatic Output: The positioner manages the supply and exhaust of compressed air to the pneumatic actuator's chambers via an internal spool or servo-valve, based on the amplified error signal.

• If the valve needs to move, the positioner increases the air pressure to one side of the actuator (for single-acting) or differentially to both sides (for double-acting).
• The high-capacity flow rate of the SHP ensures quick response and low stroking times.

6. Continuous Adjustment: This feedback loop is continuous. The positioner constantly monitors the valve's position and adjusts the air pressure until the actual position matches the desired setpoint, overcoming forces like friction and varying differential pressures to ensure high accuracy and stability.

Key Features Related to Principle

• Digital Control: The use of a microprocessor allows for sophisticated functions like auto-calibration, advanced diagnostics (online and offline), and customizable control functions (e.g., adjustable dead band, damping, and integral/derivative factors).
• Contactless Sensor: The use of a contactless magnetic feedback sensor eliminates wear and ensures reliable, precise position detection in harsh environments.
• High Flow Capacity: A high-capacity servo-valve ensures that enough air can be quickly supplied or exhausted to move even large actuators rapidly, reducing stroking times.

 Full Datasheet

Positioner Transmitter Feature  

• Manufacturer:  STI   
• Product No. : SHP-TH00ADSAL                                                                                  
• SHP - Smart High-Performance Positioner
• Pneumatic: T - Special configuration - CU-TR Intrinsically Safe
• COMMUNICATION: H - 4-20 mA and HART 7
• EXHAUST PORT: 0 - Standard
• POSITION SENSOR: 0 - Contactless Integrated
• SIGNAL FAIL POSITION: A - Fail Safe
• LOCAL INTERFACE: D - Display and push button
• TYPE & CONNECTIONS: S - High flow double/single acting - CV 2,3 - Electrical ½” NPT (qty 3) - Pneumatic ½” NPT (qty 3)
• MATERIAL: A - Aluminum low copper housing
• TEMPERATURE RANGE: L - -40°C / +85°C

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

Basic Ordering Information 

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