Description
TheWOODWARD 9907-164 is a ProTech series, digital overspeed detection system manufactured by Woodward. It functions as a dedicated, safety-critical protection device designed to monitor the rotational speed of turbines, engines, and other high-speed machinery, initiating an immediate shutdown if a dangerous overspeed condition is detected. This module is engineered with dual-channel processing and voting logic to provide extremely reliable protection, helping to prevent catastrophic mechanical failure and ensure personnel safety.
Application Scenarios
Picture a gas turbine driving a compressor on an offshore oil platform. A fuel system malfunction causes the turbine to begin accelerating uncontrollably towards a speed that could cause a catastrophic disk rupture. TheWOODWARD 9907-164 is the last line of defense. It continuously monitors speed signals from two independent magnetic pickups on the turbine shaft. Within milliseconds of either sensor detecting a speed exceeding the pre-set safety limit, the module’s solid-state safety relays de-energize, tripping the turbine’s fuel shutoff valves. In this critical role, the9907-164 doesn’t control the process; it exists solely to protect the multi-million dollar asset and the platform itself from destruction. Its value is measured not in efficiency gains, but in its flawless, fail-safe operation during the once-in-a-lifetime emergency, making it a cornerstone of functional safety in any high-speed rotating machinery installation.
Parameter
Main Parameters
Value/Description
Product Model
9907-164
Manufacturer
Woodward
Product Category
Digital Overspeed Detection / Protection System
Safety Standard
Designed to meet SIL 2 / IEC 61508 requirements.Indicates a high level of safety integrity for risk reduction.
Number of Inputs
2 Independent Speed Sensor Inputs (MPU or Proximity).Dual-channel design for redundancy and 2oo2 (2-out-of-2) voting logic.
Number of Setpoints
3 Adjustable Setpoints (Typically Warning, Danger/Trip, and Test).Allows for staged alarming and safe testing.
Outputs
2 or 3 isolated Relay Outputs (Trip, Alarm, Aux).Fail-safe relay contacts directly interface with shutdown circuits.
Analog Output
4-20 mA or 0-10 Vdc speed signal output.Provides a buffered speed signal for indication or recording.
Speed Range
Wide, configurable range (e.g., up to 9999 RPM or 30,000 PPM).Suitable for diverse machinery from slow compressors to high-speed turbines.
Power Supply
Typically 24 Vdc or 120/240 Vac.Designed for standard industrial power.
Display
Digital LED or LCD readout for real-time speed and status indication.
Key Feature
“On-The-Fly” testing capability.Allows functional testing of the trip circuit without causing an actual shutdown.
Technical Principles and Innovative Values
TheWOODWARD 9907-164 is built on the principle of fail-safe, redundant monitoring, moving beyond simple switch contacts to intelligent, configurable protection.
Innovation Point 1: Dual-Channel, 2oo2 Voting Logic for Maximum Safety. Unlike single-channel monitors, the9907-164 requires two independent speed sensors. Its core innovation is the application of 2-out-of-2 (2oo2) voting logic: a trip signal is only generated if BOTH channels simultaneously detect an overspeed condition. This architecture is critical for rejecting a spurious trip from a single failed sensor (enhancing availability) while still guaranteeing a trip on a genuine, dangerous overspeed (maintaining safety). This design directly targets the reduction of nuisance trips without compromising protection.
Innovation Point 2: Advanced Digital Signal Processing & Diagnostics. The module uses microprocessors to digitally process the raw pulse train from the speed sensors. This allows for superior noise immunity, accurate measurement even at low speeds, and advanced diagnostics. It can detect sensor faults such as a broken wire, short circuit, or loss of signal, and can annunciate these conditions independently of an overspeed event. This predictive diagnostic capability allows maintenance teams to address sensor issues before they compromise the protection system.
Innovation Point 3: “On-The-Fly” Testing and Three Configurable Setpoints. Safety systems must be testable. The9907-164 allows for a simulated overspeed test to be performed while the machine is running at normal operating speed. This tests the entire chain—sensor input, processor logic, and output relay—without causing an actual shutdown. Furthermore, its three setpoints (often Alarm, Trip, and Test) provide operational flexibility. The Alarm setpoint can provide early warning, the Trip setpoint initiates shutdown, and the Test setpoint is used for the safe functional test.
Innovation Point 4: Seamless Integration via Isolated Outputs. The module provides both safe shutdown and integration capabilities. Its failsafe relay outputs are physically isolated and can directly drive the coil of a primary shutdown solenoid valve. Simultaneously, the isolated 4-20mA output provides a high-integrity speed signal to the plant’s DCS or PLC for logging, display, and process control, eliminating the need for a separate signal conditioner and maintaining signal isolation for safety.
Application Cases and Industry Value
Case Study: Reliability Upgrade for a Refinery Turbine-Generator Set
A refinery’s steam turbine-generator, a critical unit providing plant power, was protected by an old, pneumatic overspeed trip that required frequent mechanical testing and calibration, leading to planned downtime. The system was also prone to vibration-induced spurious trips. The refinery upgraded to aWOODWARD 9907-164 digital system. The dual magnetic pickup inputs provided redundant speed sensing, and the 2oo2 logic immediately eliminated the vibration-related nuisance trips. The “On-The-Fly” test feature allowed operations to verify the trip circuit weekly in minutes without taking the unit offline. The plant engineer reported, “The9907-164 transformed our approach. We have verifiable safety without operational disruption. The diagnostic warning for a degrading sensor last month allowed us to schedule a changeout during a minor outage, avoiding a potential forced trip. Its reliability and testability are unparalleled.”
Case Study: New Installation on a Pipeline Centrifugal Compressor
For a new electric motor-driven centrifugal compressor on a long-distance gas pipeline, engineers specified theWOODWARD 9907-164 as the primary overspeed protection device. Its SIL 2 capability helped the project meet stringent international safety standards. During commissioning, the adjustable setpoints were easily configured via the front panel: a 95% speed warning for the control room, a 110% trip for the emergency shutdown system, and a 105% test setpoint. The integrated 4-20mA output was wired directly to the unit’s control panel for speed indication, saving the cost of a separate transmitter. The project manager highlighted the module’s “simplified installation and commissioning” and its “all-in-one design” that reduced wiring, panel space, and overall system complexity while delivering certified safety performance.
Related Product Combination Solutions
A complete overspeed protection or machinery monitoring system often involves components that work with theWOODWARD 9907-164.
Magnetic Pickup Sensors (MPUs) like 8252-xxxx: The primary speed sensing elements that generate the AC voltage signal read by the9907-164. A redundant pair is required.
Proximity Probes (e.g., 3300 series with drivers): An alternative to MPUs, used to sense gear teeth or key phasor marks, providing the speed signal to the9907-164.
Trip Solenoid Valve (e.g., Woodward SRV, 1501-xxx): The final element actuated by the relay contacts of the9907-164. It typically dumps control oil pressure to close the turbine’s steam or fuel valves.
Backup Mechanical Overspeed Bolt: A purely mechanical backup device on the turbine shaft, entirely independent of the electronic9907-164, representing a diverse layer of protection.
ProTech 2301D Actuator: For integrated control and protection on smaller turbines, the overspeed logic is sometimes embedded within the actuator’s electronics, whereas the standalone9907-164 is used for larger or separate applications.
PLC or DCS (e.g., Woodward NetCon, or major brand DCS): The plant’s main control system receives the 4-20mA speed signal and alarm contacts from the9907-164 for operator display and historical trending.
Dynamic Pressure Switch (for Hydraulic Trip Systems): In some older systems being retrofitted, the9907-164 may be used to energize a solenoid that vents a hydraulic trip line originally designed for a pressure switch.
Installation, Maintenance, and Full-Cycle Support
Installation of theWOODWARD 9907-164 requires careful planning for safety integrity. The module is typically panel-mounted. Critical steps include using shielded, twisted-pair cable for sensor leads, routed away from power cables to prevent noise. The two speed sensor inputs must be connected to physically independent sensors on separate power supplies or channels for true redundancy. The “Trip” output relay contacts are wired in series with the shutdown solenoid’s power circuit, ensuring that a relay de-energization (on overspeed or loss of power) causes a safe shutdown. Configuration involves setting the dip-switches or using the front keypad to define the speed range, setpoints, and output behaviors as per the safety validation calculations.
Routine maintenance is centered on periodic functional testing. The “On-The-Fly” test feature is a key maintenance tool, allowing verification of the entire electronic and output circuit. Additionally, the health of the magnetic pickups should be verified by checking their AC voltage output. The module’s front-panel diagnostics will alert to any sensor or internal fault. It is considered a life-limited device in safety systems; thus, a preventative replacement schedule (e.g., every 10-15 years) is often part of the safety plan, regardless of apparent functionality.
Our support for theWOODWARD 9907-164 recognizes its critical safety role. We provide new or certified refurbished units with full documentation. We strongly recommend and can provide support for safety lifecycle services, including assistance with proof test procedures to validate the system’s Safety Integrity Level (SIL) performance. Our experts can help with configuration guidance, wiring diagrams, and integration questions to ensure the device is installed and maintained in a way that preserves its designed safety functionality. We are committed to being a partner in maintaining the integrity of your critical machinery protection systems.
