The FOXBORO 43AP-FA42C/PB-AA is a specific configuration of the highly regarded Foxboro 43AP Pneumatic Indicating Controller. This model is designed for direct measurement and control of pressure, specifically using a bellows pressure element for its input, and features Proportional plus Integral (PI) control action.
Product Overview
The FOXBORO 43AP-FA42C/PB-AA is a Model 43AP Pneumatic Indicating Controller from Foxboro (now part of Schneider Electric). It is a classic, robust, and highly dependable analog instrument that continuously measures process pressure, compares it to a set point, and produces a proportional pneumatic (air pressure) output signal to control a final control element, typically a control valve.
Let’s break down the full model code:
- 43AP: Denotes the basic model as a Pneumatic Indicating Controller.
- -F: Indicates Field Mounting, meaning it’s designed to be mounted on a pipe or yoke, usually close to the process equipment.
- -A4: Specifies the control action as Proportional plus Integral (Reset). This is a common and effective control mode (P+I or PI) that provides a response proportional to the control error and also eliminates any steady-state offset (the difference between the setpoint and the actual process variable). The integral (reset) range is typically adjustable from 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, and a local 0 to 30 psi output gauge for visual indication of the output pressure.
- -C: Designates the Automatic Manual Internal Transfer Switching as “Bumpless”. This feature incorporates a 2-position switch, a balance gauge, and a regulator, enabling smooth and “bumpless” transfers between automatic and manual control modes without disturbing the process.
- /PB: This signifies that the controller is equipped with a Pressure (Bellows) Measuring Element for its input. This means the controller directly senses the process pressure via a robust bellows mechanism. Bellows elements are typically used for lower to medium pressure ranges.
- -AA: This specific suffix after “/PB” denotes the pressure range of the bellows element. Based on common Foxboro configurations and vendor listings, “-AA” with a /PB element typically corresponds to a pressure range such as 0 to 100 psi (or similar lower pressure ranges like 0-50 psi, 0-150 psi, often going up to around 300 psi or sometimes higher depending on specific element material/design, though helical elements /PA are for much higher pressures). Some sources indicate this configuration could also be for ranges like 0 to 100 Bar (approx 0-1500 psi), implying a helical element. It’s important to clarify if ‘PB’ in this context refers to a bellows or a broader ‘pressure element’ category that includes helicals. Given other search results for 43AP-FA42C/PB-AA explicitly state “SS Gauge Pressure Element Calibrated 0-250PSIG” or “Helical Element Calibrated 0-1500 psig”, it seems there can be variations on the specific range associated with “AA” and whether it strictly refers to bellows or can encompass helical for certain pressure configurations. For the most precise information, the specific data sheet for the exact unit or its label would be ideal.
This particular configuration makes it highly suitable for direct measurement and control of process pressures, typically in lower to medium ranges, offering a local, intrinsically safe, and reliable control solution with P+I action.
Technical Specifications
Main Features and Advantages
The FOXBORO 43AP-FA42C/PB-AA offers a robust set of features, particularly due to its direct pressure measurement capability and pneumatic design:
Direct Process Pressure Measurement (/PB-AA): This is a defining characteristic. The controller directly senses and indicates process pressure via its internal bellows (or sometimes helical) element, calibrated for its specific range (e.g., 0-100 psi, or higher depending on the specific element). This eliminates the need for a separate pressure transmitter, simplifying the control loop and offering potentially faster response for pressure control applications.
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., in oil & gas, chemical plants) without requiring costly additional safety barriers or specialized enclosures. Its mechanical design also contributes to its exceptional durability in harsh industrial conditions.
Proven Reliability and Longevity: The Foxboro 43AP series has an extensive track record of reliable and continuous operation in demanding industrial environments, known for its robustness and long operational life.
Proportional plus Integral (Reset) Control (A4): The “A4” control action provides the essential combination of proportional response (to the magnitude of the error) and integral action (to eliminate any 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 is a critical operational feature, allowing 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 during mode changes.
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 near the pressure tap or control valve, which simplifies pneumatic piping and can improve responsiveness.
Application Field
The FOXBORO 43AP-FA42C/PB-AA is primarily utilized in process industries that rely on pneumatic instrumentation for direct, robust, and reliable pressure control, especially within its specified pressure range.
Chemical and Petrochemical Plants:
- Controlling pressures in distillation columns, tanks, or utility lines where precise and stable control is crucial.
- Ideal for hazardous areas where intrinsic safety is a primary concern.
Oil and Gas Production and Refining:
- Managing pressures in separators, flare lines, or low-to-medium pressure vessels.
- Controlling gas Blanket pressure on storage tanks.
Water and Wastewater Treatment:
- Controlling pressures in filtration systems, distribution networks, or digesters.
Manufacturing:
- Controlling air or gas pressure in various industrial processes, e.g., for pneumatic conveying or system pressure regulation.
In essence, the 43AP-FA42C/PB-AA is employed wherever a direct, continuous, closed-loop control of process pressure within its range (e.g., 0-100 psi, or higher if a helical variant) is needed, and the inherent safety, reliability, and local indication capabilities of a pneumatic controller are highly valued.
