Product Introduction: 3500/72 140734-08
The 3500/72 140734-08 is an Analog-to-Tachometer Interface Module for the Bently Nevada 3500 Machinery Protection System. This specialized module serves as a signal conditioner and converter, bridging the gap between analog tachometer sensors and the digital monitoring framework of the 3500 system.
Its primary function is to accept a raw AC sine wave or pulse signal from various speed-sensing devices (such as magnetic pickups, photoelectric sensors, or proximity probes) and convert it into two key outputs: a clean, digital tachometer pulse for the rack's internal Keyphasor reference, and a proportional 4-20 mA analog output representing rotational speed. This enables precise speed monitoring, overspeed protection, and provides a phase reference for machinery diagnostics.
Detailed Parameters & Specifications
The following table summarizes the key physical and technical specifications of the module:
| Parameter Category | Specification Details |
|---|---|
| Part Number | 140734-08 |
| Functional Designation | 3500/72 Analog-to-Tachometer Interface Module |
| Physical Dimensions (H x W x D) | Approximately 200 mm x 60 mm x 220 mm (Standard 3500 series 4-channel module slot size) |
| Weight | Approximately 0.85 kg (1.87 lbs) |
| Power Requirements | Powered directly from the 3500 rack backplane. Typical consumption: +5V DC. |
| Operating Temperature | -30°C to +65°C (-22°F to +149°F) |
| Input Signal | Accepts raw AC signals from: • Magnetic Pickups (MPUs) • Proximity Probes • Photoelectric Sensors Frequency Range: Typically 0.5 Hz to 20,000 Hz. |
| Primary Outputs | 1. Digital Tach Pulse (Keyphasor): A conditioned, TTL-compatible once-per-revolution pulse distributed via the rack backplane. 2. Analog Output: A proportional 4-20 mA signal representing 0 to the configured full-scale speed (e.g., 0-5000 RPM). |
| Key Functions | • Speed Measurement: Provides RPM value to the monitoring system. • Overspeed Detection: Can be used as an input for overspeed protection channels. • Signal Conditioning: Converts noisy or low-amplitude sensor signals into clean, usable digital and analog outputs. |
| Configuration | Configurable via 3500 rack configuration software for parameters such as pulses per revolution, full-scale speed, and signal filtering. |
| LED Indicators | Provides status LEDs for Power, OK, Signal Present, and Fault. |
Primary Application Scenarios
The 3500/72 module is essential in applications requiring reliable speed sensing for protection, control, and diagnostics:
Overspeed Protection Systems:
Key Application: Serves as the primary or redundant speed input for 3500/50 Overspeed Protection Modules. It provides the critical speed signal used to initiate an emergency shutdown if the rotor exceeds a safe maximum speed, protecting turbines and turbo-compressors from catastrophic mechanical failure.
Speed Monitoring and Control:
Key Application: The 4-20 mA analog output provides a continuous speed signal to the plant's Distributed Control System (DCS) or Programmable Logic Controller (PLC) for process control, performance calculation, and operational monitoring.
Phase Reference for Vibration Analysis:
Key Application: When used with a once-per-revolution sensor, its digital tach pulse output acts as the Keyphasor® reference for the entire 3500 rack. This enables synchronous vibration analysis, startup/coast-down (Bode/Nyquist) plots, and orbit displays for diagnostic purposes.
Integration with Non-Standard Sensors:
Key Application: Allows the integration of legacy or non-Bently Nevada speed sensors (e.g., certain magnetic pickups or gear tooth sensors) into the modern 3500 monitoring framework by conditioning their raw signals into a format the system can use.
Redundant Speed Sensing:
Key Application: Used in pairs or trios to provide redundant speed inputs for high-reliability voting systems (e.g., 2-out-of-3 voting for overspeed trips), ensuring protection system availability and preventing spurious trips.
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