Flowserve Positioner LOGIX 3800 Series - 3821-34EAD43L-1110-00

The LOGIX 3800 digital positioner works by receiving a control signal (like a \(4-20mA\) input) to precisely control a valve's position using air pressure. It achieves this through its core components: a non-contact position feedback system, a double-poppet relay for high air capacity, and an I/P piezo driver module. The positioner continuously monitors the valve's position using sensors and adjusts pneumatic pressure to move the valve to the desired setpoint, while advanced diagnostics provide predictive warnings about potential issues. 

Core working principle

• Receives control signal: The positioner takes an input signal, such as a \(4-20mA\) signal with HART communication, to determine the desired valve position. 
• Monitors valve position: It uses a non-contact feedback mechanism to continuously measure the actual valve position. 
• Calculates and adjusts pressure: A digital processor compares the desired position with the actual position. It then signals the I/P piezo driver module to regulate pneumatic pressure, which is delivered through the double-poppet relay to the actuator. 
• Moves the valve: The adjusted air pressure moves the valve to the correct position. The double-poppet technology allows for high air capacity, ensuring efficient and responsive movement. 

Key features and their function

• Double-poppet technology: This feature provides high air capacity with minimal air consumption, resulting in efficient operation.  
• Non-contact feedback: This ensures a longer service life and reliability by preventing wear and tear from a physical linkage.  
• Five pressure sensors: These sensors allow the device to monitor the health of the valve and actuator, identifying developing problems before they cause a critical failure.  
• Backup control mode: For models with Pro software, if the position feedback linkage is broken, the positioner can switch to a backup mode and estimate the valve position using actuator pressure, allowing for continued operation at a reduced performance level.
• QuickCal feature: This one-button calibration simplifies commissioning by automatically configuring the valve's zero, span, and gain.
• Advanced diagnostics: The positioner performs continuous health monitoring and provides predictive warnings about potential issues through an integrated display or remote connection via ValveSight DTM

Key components and their function

• Magneto-resistive position sensor: This non-contact, dual-element sensor continuously measures the valve's actual position. It is shielded to be robust against vibration and environmental factors, ensuring reliability in tough conditions.
• Electronic control module: The module is the "brain" of the positioner. It takes the input control signal (e.g., a 4–20 mA current or a digital signal via a fieldbus protocol) and compares it to the feedback from the position sensor. Based on this comparison, it calculates the necessary adjustments to be made to the air supply.
• Dual-poppet pneumatic relay: This component regulates the air pressure sent to the valve actuator. Using a temperature-compensated, dual-poppet design, the relay delivers a high volume of air quickly to the actuator, providing fast and precise valve movement. This design also significantly reduces air consumption compared to older designs.
• Valve actuator: The Logix 3800 mounts directly to the valve actuator, which can be either single-acting (spring-return) or double-acting. It is the mechanical device that actually moves the valve.
• Five on-board pressure sensors: These sensors are used for advanced predictive diagnostics, allowing the device to detect developing problems in the valve and actuator assembly before they cause a critical failure.

The operating cycle

1. Input signal reception: The positioner receives a command signal from a control system, such as a Distributed Control System (DCS). This signal typically specifies the desired position for the valve (e.g., a 4–20 mA current signal where 4 mA is 0% open and 20 mA is 100% open).
2. Position sensing: The non-contact magneto-resistive sensor provides continuous feedback on the valve's actual position to the electronic control module.
3. Error calculation and control: The control module compares the received command signal with the actual position feedback. It then calculates the error and sends a corresponding electrical signal to the pneumatic relay.
4. Pneumatic pressure adjustment: The pneumatic relay receives the electrical signal and regulates the flow of air into or out of the valve actuator.

• For a single-acting actuator: The relay controls the air supply to either drive the valve open or release air to allow a spring to close it.
• For a double-acting actuator: The relay directs air pressure to one side of the actuator's piston and exhausts air from the other side to move the valve in the desired direction.

5. Valve movement and feedback: The change in air pressure causes the actuator to move the valve. The position sensor continuously monitors this movement, providing real-time feedback to the control module to ensure the valve reaches and holds the precise target position.
6. Diagnostics: The integrated pressure sensors and diagnostic algorithms continuously monitor the valve's performance, checking for issues like friction, leakage, and backlash. This provides proactive maintenance data to operators.

 Full Datasheet

Positioner Transmitter Feature  

• Manufacturer: LOGIX 3800
• Product No. :  3821-34EAD43L-1110-00
• 3821 - Logix 3800 Series (38), Communication HART (2), Housing  Aluminum – Ex d (1)
• Certifications: 34 -FM/US/Canada Ex Proof Class and Division B-D to -40°C; Ex d IIC -50°C Intrinsically Safe and Non-Incendive IIC to -55°C5,8
• Threaded Connections: E - Mounting: 5/16" 18 UNC, Pneumatics: 1/4" NPT, Conduit: 1/2" NPT, Vents 1/4" NPT
• Actuation Medium: A - Air
• Relay Type: D - Double Acting, Standard
• Actuator Action: 4 - Four-Way (Double Acting)
• Pressure Gauges: 3 - SS with Brass Internals. psi (bar/kPa) Sealed and purged
• Gauge Orientation: L - Gauges oriented for display on the left side of the positioner.
• Diagnostics: 1 -Pro-Diagnostics (Full Functionality)
• Display: 1 - LCD
• Feedback Shaft: 1 - D - 316 Stainless Steel Shaft (Valtek Standard)
• Mounting: 0 -Standard Mounting
• Special Options: 00 -No Special Options

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

Basic Ordering Information