Description
Product Introduction & Engineering Value
I’ve seen these cards used on turbine and critical valve positioning systems where precise closed-loop control of a hydraulic or pneumatic servo is required. The FBMSVH accepts a process command (typically 4-20 mA or 0-10 V) and an LVDT position feedback signal. It then applies proportional or proportional-plus-integral control to generate a bipolar current output (commonly ±27 mA) that drives the servo valve.
The card is intended for integration into Foxboro I/A Series or related control architectures that need dedicated electro-hydraulic interface capability. External ±15 V power is normally required. It provides adjustable zero and span, LVDT excitation, and external shutdown contact inputs.
Technical Specifications
Command Input: Selectable 4-20 mA or 0-10 V DC (zero and span adjustable)
Feedback Input: LVDT (0-10 V typical) with onboard modulator/demodulator
Output: ±27 mA (typical) to drive servo valve
Control Modes: Proportional (P) or Proportional + Integral (P+I)
Additional Features: External shutdown contacts, adjustable LVDT excitation amplitude, optional 0-20 mA valve position retransmission
Power Supply: External ±15 V DC
Operating Temperature: Typically 0 to 50 °C (confirm specific revision)
Form Factor: Control card style for system integration
Field Application & The “Trench” Experience
A power generation site needed reliable closed-loop positioning of a critical steam admission valve. The existing interface had drifted and was difficult to calibrate. An FBMSVH card was installed, the LVDT feedback and 4-20 mA command connected, and the P+I loops adjusted. After tuning the zero, span, and excitation, the valve tracked the demand signal accurately with stable positioning under varying load conditions. The external shutdown input was wired into the trip system for additional protection.
Typical niche applications:
- Closed-loop positioning of hydraulic or electro-hydraulic servo valves on steam turbines
- Precise control of critical process valves that use LVDT feedback
- Retrofit of aging DEH (Digital Electro-Hydraulic) interfaces in power or process plants that still rely on analog servo drive signals
FBMSVH
FBMSVH
Transparency SOP: QA & Testing
- Visual inspection of the card, connectors, and labeling.
- Power-up with external ±15 V supply and basic functional verification.
- Command input test (both current and voltage ranges) with zero/span adjustment confirmation.
- LVDT excitation and feedback demodulation check.
- Output current verification into a simulated servo load across the bipolar range.
- Shutdown input and overall loop response test under controlled conditions.
The Veteran’s Tech Trap Guide
⚠️ External ±15 V power is required. The card does not operate from the standard 24 V Module Fieldbus supply. Missing or incorrect bipolar power is the most common reason the card appears completely dead after installation.
PRO TIP: Confirm the LVDT excitation amplitude and phase before final tuning. An incorrect excitation setting produces noisy or non-linear feedback that makes the loop difficult or impossible to stabilize.
⚠️ Match the command signal type. The card supports both 4-20 mA and 0-10 V commands, but the selection and zero/span adjustments must be set correctly for the actual signal coming from the control system. A mismatch produces incorrect valve positioning.
Dynamic FAQ
Q: What type of device does the FBMSVH primarily control? A: It is designed as a closed-loop interface for servo valves that use LVDT position feedback, commonly found in electro-hydraulic positioning systems.
Q: What power supply does the card require? A: External ±15 V DC is required for normal operation.
Q: Can the command input be either current or voltage? A: Yes. The card accepts selectable 4-20 mA or 0-10 V DC command signals with adjustable zero and span.
Q: Does the card provide a valve position retransmission signal? A: Many versions offer an optional 0-20 mA valve position output for monitoring or recording.
Q: Are New Surplus FBMSVH units original Foxboro / Invensys product? A: Yes. Units are original OEM material that have passed functional testing of command input, LVDT interface, and servo output drive.
Q: What warranty is provided? A: 12-month warranty against defects in materials and workmanship from the date of shipment for both New Surplus and fully tested refurbished units.
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