Woodward ESSE2-LL | Electronic Speed Switch

The Woodward ESSE2-LL (Electronic Speed Switch, 2-Channel, Low-Logic) is a high-speed, DIN-rail mountable safety device designed to monitor the rotational speed of engines, turbines, and industrial machinery. It utilizes incoming signals from a Magnetic Pickup (MPU) to provide localized protection. The ESSE2-LL features two independent trip relays that can be programmed to trigger at specific RPM thresholds, serving as a critical safety barrier to initiate shutdowns or alarms during overspeed or underspeed events.

⚙️ Product Specifications

• 🧩 Manufacturer: Woodward
• 🔢 Model Number: ESSE2-LL
• 🏷️ Product Type: Dual-Channel Electronic Speed Switch
• 📐 Dimensions: 110 mm x 99 mm x 22.5 mm (4.33″ x 3.90″ x 0.89″)
• ⚖️ Weight: 0.15 kg (0.33 lbs)
• 🗺️ Country of Origin: USA
• ⚡ Operating Input Voltage: 10–30 VDC
• 📉 Power Consumption: 2 Watts maximum
• 🔌 Output Type: 2 x Form C Electromechanical Relays
• 🛡️ Isolation: Galvanic isolation between speed signal and power/output circuits

🏭 Applications

• 🛡️ Emergency Overspeed Trip: Providing an independent, hardware-based safety trip for turbines when the primary governor fails.
• ⚙️ Crank Termination: Automatically disengaging the starter motor once the engine reaches a set “firing” RPM.
• 🛑 Under-speed Monitoring: Detecting mechanical stalls or load-induced slowdowns in critical pump and fan applications.
• 🔄 Sequential Logic: Triggering auxiliary cooling systems, intake shutters, or oil pressure bypasses based on real-time RPM thresholds.

🛑 Power Sequencing & Setup

🔌 Installation Sequence

• 🔧 Securely snap the ESSE2-LL onto a standard 35 mm DIN rail inside a vibration-dampened control cabinet.
• 🔧 Connect the Magnetic Pickup (MPU) signal wires to the designated input terminals.
• 🔧 Wire the relay contacts to your machine’s safety PLC or emergency shutdown (ESD) relay string.
• ⚡ Apply 24 VDC power to the input terminals. The “Power” LED should illuminate immediately.
• 🛠️ Use the onboard configuration interface (or handheld programming tool) to input the gear tooth count and desired trip RPM for Trip 1 and Trip 2.

🏃 Operation & Trip Logic

• Step 1: Signal Conditioning: The device receives a continuous frequency signal from the MPU.
• Step 2: Threshold Comparison: The internal microprocessor compares the current frequency against the user-programmed “Setpoints.”
• Step 3: Relay Action:
  • If speed exceeds the setpoint, the corresponding relay trips (changes state).
  • The ESSE2-LL is often configured for “Fail-Safe” operation, meaning the relay is energized during normal operation and drops out (de-energizes) during an overspeed event or power loss.
• Step 4: Reset: Depending on settings, the relay can either auto-reset when speed drops back below the trip threshold (with hysteresis) or latch until a manual reset is performed.

🔧 Programming & Calibration

• 💻 Configuration: Programming is typically done via an external communication adapter or direct interface buttons (depending on the specific sub-version).
• 💻 Hysteresis: Always program a “deadband” (hysteresis) of 2–5% to prevent relay chatter or nuisance trips when the engine speed fluctuates slightly around the trip setpoint.
• 💻 Verification: Use a frequency generator to simulate MPU pulses and confirm that the relays trigger exactly at the target RPM before connecting the device to live machinery.

❓ Frequently Asked Questions (Q&A)

• Q: My speed switch triggers a trip even when the engine is running at normal speed. Why?
  • A: This is often caused by “Electrical Noise” (EMI). Ensure the MPU cable is shielded, the shield is grounded at the cabinet end only, and that the cable is not running in the same conduit as AC power lines.
• Q: Can I use this to replace a mechanical overspeed bolt?
  • A: Yes, many modern industrial standards allow for electronic speed switches as part of a high-integrity safety system, provided they are regularly tested and calibrated.
• Q: What does the “LL” in the model number stand for?
  • A: “LL” typically refers to “Low Logic” or specific configuration variants regarding trip logic and signal input range; always refer to the specific unit’s manual for your exact logic configuration.

📦 Recommended Related Components

• Woodward 1325-01.5 (Magnetic Pickup)
• Woodward 0199-001 (Shielded MPU Cable)
• Woodward 8271-442 (ProAct Actuator Driver)