Woodward SMM40 | Speed Adjusting Motor

The Woodward SMM40 is a ruggedized, precision-controlled electric actuator used primarily for the remote adjustment of speed settings on legacy mechanical governors. It is designed to interface with the speed-setting linkage of industrial governors, allowing operators to increase or decrease the prime mover’s target RPM from a remote control station or Distributed Control System (DCS). The SMM40 provides fine-tuned, incremental control, making it essential for synchronization and frequency matching in parallel generator operations.

⚙️ Product Specifications

• 🧩 Manufacturer: Woodward
• 🔢 Model Number: SMM40
• 🏷️ Product Type: Remote Speed Adjusting Motor
• 📐 Mounting: Flange or bracket mount (application-dependent)
• ⚖️ Weight: 0.85 kg (1.87 lbs)
• 🗺️ Country of Origin: USA
• ⚡ Operating Input Voltage: 24 VDC (Standard)
• 🔌 Output Torque: High-torque geared drive (specific to governor linkage resistance)
• 🛡️ Enclosure: Industrial-grade, dust-tight, and moisture-resistant casing

🏭 Applications

• ⚡ Generator Synchronization: Precise manual or auto-control of generator speed to match bus frequency during paralleling.
• 🚢 Marine Throttle Control: Remote RPM management for shipboard propulsion and auxiliary engines from the helm.
• 🛢️ Mechanical Drive Control: Remotely adjusting the setpoint of legacy mechanical governors on process pumps and compressors.
• 🏭 Plant Microgrids: Integrating older mechanical governor systems into modern digital plant control architectures.

🛑 Installation & Linkage Setup

🔧 Mechanical Integration

• Alignment: The SMM40 must be mounted such that the output shaft is perfectly aligned with the governor speed-setting lever. Misalignment will cause premature wear on the motor’s internal geartrain.
• Linkage: Use a ball-joint rod linkage to connect the motor arm to the governor lever. Ensure that the total travel of the SMM40 matches the required range of the governor’s speed-setting lever to prevent mechanical binding.
• Stop Limits: Most installations utilize external travel limits or internal electrical limit switches to prevent the motor from driving the governor lever past its physical mechanical stops.

🔌 Electrical Setup

• Directionality: Ensure the DC polarity is wired correctly; reversing the polarity will reverse the “Increase” and “Decrease” commands.
• Protection: It is standard practice to wire an isolation relay or a “Raise/Lower” toggle switch to prevent the motor from being continuously energized after the desired speed setpoint is reached.

🏃 Operational Procedure

• Step 1: Verify the governor is in “remote speed adjust” mode.
• Step 2: Apply a short pulse of 24 VDC to the “Raise” or “Lower” terminals to nudge the speed setpoint.
• Step 3: Observe the tachometer or frequency meter to verify the desired shift in RPM.
• Step 4: Once the target speed or frequency is achieved, terminate the voltage signal to hold the current position.

🔧 Maintenance & Troubleshooting

• Issue: Motor hums but speed does not change.
  • Check: Possible stripped internal gears or a disconnected mechanical linkage rod.
• Issue: Motor fails to respond in one direction.
  • Check: Inspect the “Raise/Lower” control relay contacts and ensure wiring continuity to the motor terminals.
• Issue: Speed drifts while running.
  • Check: Inspect the linkage for excessive play (slop) and verify that the motor’s holding torque is sufficient to overcome the governor spring tension.

❓ Frequently Asked Questions (Q&A)

• Q: Can the SMM40 be used as a primary governor actuator?
  • A: No. The SMM40 is designed only to adjust the setpoint of an existing mechanical governor. It is not fast enough to serve as the primary fuel-metering actuator.
• Q: Does this motor have internal limit switches?
  • A: Yes, most SMM40 variants include internal limit switches to cut power when the motor reaches the end of its travel stroke, preventing damage to the motor or the governor linkage.
• Q: Can I use a PWM signal to control this motor?
  • A: No. The SMM40 is a simple DC-brushed motor device; it requires constant DC voltage to drive the internal gear reduction, not a PWM or 4-20mA control signal.

📦 Recommended Related Components

• Woodward 2301A Load Sharing Controller (for automatic setpoint control)
• Woodward 0199-001 (Shielded MPU Cable)
• Woodward Magnetic Pickup (MPU)