The FOXBORO 43AP-FA42C/PB-AA is a specific configuration of the classic Foxboro 43AP Pneumatic Indicating Controller. This model is distinguished by its direct connection to a Pressure (Bellows) Measuring Element and specific control and transfer options.
Product Overview
The FOXBORO 43AP-FA42C/PB-AA is a Model 43AP Pneumatic Indicating Controller, manufactured by Foxboro (now part of Schneider Electric). This instrument is a robust and reliable analog device designed for continuous measurement, indication, and control of pressure in industrial processes using air pressure signals. It compares the measured pressure to a user-defined set point and generates a proportional pneumatic output signal to operate a final control element, typically a control valve.
Let’s break down the full model number:
- 43AP: Denotes the basic model, a Pneumatic Indicating Controller.
- -F: Indicates Field Mounting, meaning it is designed to be mounted on a pipe or yoke, typically close to the process or control valve.
- -A4: Specifies the control action as Proportional plus Integral (Reset). This combination (P+I or PI control) provides a proportional response to the error and also eliminates steady-state offset (the difference between the setpoint and the actual process variable). The integral (reset) range is typically 0.01 to 50 minutes per repeat.
- -2: Refers to the Output Signal and Gauge: a standard 3 to 15 psi (pounds per square inch) pneumatic output air signal, with a local 0 to 30 psi output gauge for visual feedback.
- -C: Designates the Automatic Manual Internal Transfer Switching as “Bumpless”. This feature includes a 2-position switch, a balance gauge, and a regulator, allowing for smooth transfer between automatic and manual control modes without disturbing the process.
- /PB: This is the crucial part. It indicates that the controller is equipped with a Pressure (Bellows) Measuring Element for its input. This means the controller directly measures process pressure by converting the pressure into a mechanical motion via bellows, which then drives the controller’s mechanism.
- -AA: This suffix typically indicates specific ranges or options for the PB (Pressure Bellows) element. While the exact range isn’t universally defined by “AA” without a Foxboro catalog, it usually signifies a common or standard pressure range (e.g., 0-15 psi, 0-30 psi, 0-100 psi, etc.) for the bellows. This implies the controller is designed to directly measure and control process pressure within that specific range.
This specific configuration makes it ideal for direct control of pneumatic pressure lines, vessel pressures, or other process pressures where a local, robust, and intrinsically safe control solution is desired.
Technical Specifications
Main Features and Advantages
The FOXBORO 43AP-FA42C/PB-AA offers a distinct set of features and advantages, primarily stemming from its direct pressure measurement capability and pneumatic design:
Direct Process Pressure Measurement (/PB): This is the defining feature. The controller directly senses process pressure via its internal bellows element. This eliminates the need for a separate pressure transmitter, simplifying the control loop, reducing components, and potentially minimizing signal lag for responsive control of pressure.
Inherent Safety and Robustness: As a purely pneumatic instrument, it is intrinsically safe and immune to electrical noise, electromagnetic interference (EMI), and radio frequency interference (RFI). This makes it exceptionally well-suited for hazardous (explosion-proof) environments (e.g., oil & gas, chemical plants) without requiring additional safety barriers or specialized enclosures.
Proven Reliability: The Foxboro 43AP series has a long-standing reputation for robust and dependable operation in harsh industrial conditions. Its mechanical design contributes to its durability and resistance to environmental factors like extreme temperatures and vibration.
Proportional plus Integral (Reset) Control: The “A4” control action provides both proportional response (to the magnitude of the error) and integral action (to eliminate steady-state offset). This ensures precise and stable control, allowing the process pressure to accurately reach and maintain its setpoint over time.
Bumpless Auto/Manual Transfer (“C” option): This crucial operational feature allows operators to seamlessly switch between automatic and manual control modes without introducing sudden changes or disturbances to the pneumatic output and thus to the process. This significantly enhances operational stability and minimizes process upsets.
Local Indication: The controller provides a direct, mechanical indication of the measured process pressure, the set point, and the output control signal. This allows operators to quickly monitor and assess the process status directly in the field, independent of a central control system.
Field Mountable (“-F”): Designed for mounting directly on a pipe or yoke, typically close to the pressure tap or control valve. This simplifies pneumatic piping and can enhance control loop responsiveness due to shorter signal lines.
Low Maintenance Requirements (for trained personnel): While regular calibration and clean air are essential, pneumatic instruments generally have fewer delicate electronic components. This often leads to simpler troubleshooting and repair compared to complex electronic systems, provided technicians are familiar with pneumatic principles.
Application Field
The FOXBORO 43AP-FA42C/PB-AA is specifically designed for applications requiring direct, robust, and reliable pneumatic control of pressure. Its primary application fields are in process industries that utilize pneumatic instrumentation:
Oil and Gas Industry:
- Wellhead Control: Direct pressure control for various wellhead parameters.
- Pipeline Pressure Regulation: Maintaining specific pressures in gas or liquid pipelines.
- Vessel Pressure Control: Regulating pressure in separators, knock-out drums, and storage tanks.
- Refineries and Petrochemical Plants: Controlling pressures in distillation columns, reactors, and various process vessels, particularly in areas where the intrinsic safety of pneumatic devices is a key advantage.
Chemical Processing:
- Controlling reaction vessel pressures, header pressures, and line pressures within chemical synthesis units.
- Managing pressure in storage tanks for various chemicals.
Power Generation (Traditional Plants):
- Controlling steam pressure, feedwater pressure, or fuel gas pressure in older boiler systems and balance of plant auxiliary systems.
- Pressure regulation for seal steam systems or other utility applications.
Pulp and Paper Industry:
- Controlling steam pressures, digester pressures, or air pressures in various process stages.
Water and Wastewater Treatment:
- Regulating pressure in water distribution networks, pumping stations, or treatment process lines.
In essence, the 43AP-FA42C/PB-AA is employed wherever a direct, continuous, closed-loop control of a pneumatic pressure is needed, and the inherent safety, reliability, and local indication capabilities of a pneumatic controller are highly valued.
Related Products
The FOXBORO 43AP-FA42C/PB-AA operates as a standalone pressure controller within a pneumatic control loop. Its related products primarily involve the final control element and the necessary air supply system.
Primary Connecting Instruments:
- Pneumatic Control Valves: These are the final control elements that receive the 3-15 psi output signal from the 43AP-FA42C/PB-AA to manipulate the process pressure. They typically consist of:
- A valve body (e.g., globe valve, butterfly valve) suited for pressure control.
- A pneumatic actuator (diaphragm or piston type) that converts the air signal into mechanical force to move the valve.
- Often, a pneumatic valve positioner (e.g., Foxboro 69P or 69F) mounted on the valve. While the 43AP-FA42C/PB-AA provides a direct 3-15 psi output, a positioner improves control valve accuracy and overcomes friction.
Pneumatic Infrastructure and Accessories:
- Instrument Air Supply System: Essential for providing clean, dry, and regulated air to the controller:
- Air Filters and Dryers: Crucial for removing moisture, oil, and particulates from the compressed air, preventing internal clogging and corrosion.
- Air Regulators: To reduce the plant air supply pressure (e.g., 80-100 psi) to the required 20 psi for the controller. The 43AP-FA42C/PB-AA often incorporates an integral air supply set, but external regulation might also be present.
- Pneumatic Tubing and Fittings: For routing the instrument air supply and the output signal to the control valve.
- Pneumatic Relays and Boosters: If the control valve is large or needs to actuate very quickly, a pneumatic relay or volume booster might be used to amplify the 3-15 psi signal from the controller and provide a higher air volume to the actuator.
Other Foxboro 43AP Variations:
- While this model has a direct pressure (bellows) input, other 43AP models have different internal measuring elements for direct connection, such as helical or spiral elements for higher pressures, or filled thermal systems for direct temperature measurement.
- Models with different control modes (e.g., Proportional only, Proportional + Derivative).
Interface Components (for hybrid systems):
- Pneumatic-to-Electric (P/I) Converters: If the pneumatic output (3-15 psi) from the 43AP-FA42C/PB-AA needs to be transmitted to a modern electronic Distributed Control System (DCS) or Programmable Logic Controller (PLC) that uses electrical signals (e.g., 4-20mA).
- Electric-to-Pneumatic (I/P) Converters: These would typically be used if a modern electronic controller or DCS needed to send a signal to a pneumatic control valve that the 43AP-FA42C/PB-AA might be cascading with or overseeing.
Calibration and Test Equipment:
- Pneumatic Calibrators: Used to generate and measure precise pneumatic pressures for calibrating the controller and its associated control valve/positioner.
- Pressure Gauges and Manometers: For verifying input/output pressures and detecting leaks during maintenance.
