Description

The Woodward 1680-622 is a high-output, passive Magnetic Pickup (MPU) sensor designed to monitor rotational speed within industrial prime movers, such as gas turbines, steam turbines, and large internal combustion engines. Operating on electromagnetic induction principles, the sensor detects the passage of ferrous gear teeth (or slots) on a target wheel and generates an alternating current (AC) voltage signal. The frequency of this output signal is directly proportional to the rotational speed of the shaft, providing precise, real-time speed data to Woodward governors, digital control systems (e.g., MicroNet or 723PLUS), or generic frequency-to-current converters.

Technical Specifications

Procurement & Commercial Availability

• Condition: New Original (Factory Boxed) or Clean Surplus. Certified pre-owned variants undergo rigorous coil resistance and insulation checks before distribution.
• Warranty: 12-month standard industrial warranty covering physical defects and electrical performance bounds.
• Lead Time: In-stock components ship globally within 1 to 3 business days from receipt of a purchase order.
• Pricing Notice: Listed prices across industrial distributors are indicative. Final transaction pricing varies with supply dynamics; contact us for a firm quotation.

Field Commissioning & Mechanical Constraints

Sensor Air Gap Adjustment

The strength of the AC voltage waveform generated by the 1680-622 is heavily dependent on the mechanical air gap between the pole piece tip and the gear tooth apex. If the air gap is too wide, the signal amplitude will drop below the control system’s minimum sensing threshold (typically 1.0 to 1.5 V RMS), leading to “loss of speed” trips during low-RPM engine cranking.

Standard Field Calibration Procedure: Thread the 1680-622 into the housing bracket until the pole piece makes direct, finger-tight contact with the high point of a gear tooth. Back the sensor out by 1/2 to 3/4 of a turn to establish an approximate 0.025-inch to 0.035-inch (0.64 mm to 0.89 mm) clearance window. Fasten the external jam nut securely to prevent drift from high-frequency structural vibration.

Electrical Interconnection and Noise Mitigation

Because the 1680-622 is a passive, unamplified sensor, its millivolt-level output at low speeds is highly susceptible to electromagnetic interference (EMI) from nearby high-voltage lines, variable frequency drives (VFDs), and ignition wiring.

• Wiring Specification: Connect the sensor using a twisted, shielded pair cable (such as Belden 8761).
• Shield Grounding: Ground the cable shield wire only at the control system end. Terminating or grounding the shield at both ends creates ground loops that introduce harmonic noise into the speed-sensing circuit.

Frequently Asked Questions

What happens if the internal resistance deviates from the 250-ohm specification?

An open circuit (\infty ohms) indicates a broken internal copper winding, rendering the sensor useless. A resistance value significantly lower than 250 ohms suggests a short circuit within the internal coil layers, which reduces signal amplitude and alters output impedance. Replace any sensor demonstrating unexpected resistance swings outside a \pm10\% variance at ambient room temperature.

Is the 1680-622 interchangeable with the 1680-631 MPU?

No, they are not direct structural drop-ins. While both sensors share the 0.625-18 UNF thread style and a 250-ohm nominal coil setup, the 1680-631 features a shorter 3.5-inch insertion depth and holds specific CSA Division 1 hazardous location certifications via integrated 10-foot lead wires. Verify clearance profiles and compliance boundaries before substituting.