Product Overview
The Bently Nevada 3500/70M 136449-09 is the dedicated reciprocating-machine monitor inside the Bently Nevada 3500 Machinery Protection System, and it exists for one honest reason: a reciprocating compressor does not vibrate the way a turbine does. Where a steam turbine produces a more or less continuous, sinusoidal shaft orbit, a reciprocating compressor delivers short, hard impacts separated by quiet dwell — valve slap, crosshead reversal, piston kiss, rod-drop, crank-web clearance events — and a conventional proximitor or seismic monitor, tuned for smooth 1X content, will either filter that impulse into nothing or report it as a pile of broad-band hash. The Bently Nevada 3500/70M 136449-09 was built to keep the impulse and throw away the ringing. It is a full-height, four-channel card that takes the raw charge or voltage output of a seismic velocity transducer or accelerometer, runs it through programmable high- and low-pass filtering and an eight-revolution smoothing average, and derives the static values that actually describe the machine’s health.
Each of the four channels on the Bently Nevada 3500/70M 136449-09 is software-selectable among four measurement personalities: Impulse Acceleration, Acceleration 2, Reciprocating Velocity, and Low-Frequency Reciprocating Velocity. The channels are programmed as a pair, so channels 1 and 2 can run Impulse Acceleration on the two crosshead-guide points of a frame while channels 3 and 4 run Low-Frequency Recip Velocity on the crankcase, all from one module and one backplane slot. That pairing is not a compromise — it is the product’s central commercial and engineering advantage, because a single compressor frame typically needs exactly that mix: high-frequency impact detection to catch a failing discharge valve, and low-frequency frame-velocity trending to catch a loosening foundation or a cracked crankcase before the vibration becomes structural. Every active static value gets an Alert setpoint, and any two may carry a Danger setpoint with independently configurable 1–60 second Alert and 0.1–60 second Danger delays, so a single noisy valve event cannot trip the rack while a genuinely growing trend still drives the Danger path.
Integration is deliberately boring, which is exactly what a protection engineer wants at 2 a.m. The 3500/70M 136449-09 draws its −22 Vdc transducer supply from the rack backplane, publishes its static values and alarm state to the rest of the frame, and presents one BNC buffered-transducer output per channel plus a user-selected 4–20 mA recorder output per channel for the DCS or a standalone trend logger. Configuration lives in the 3500 Rack Configuration Software and is stored in non-volatile memory, so a replacement card comes back on-line with the original filter corners, sensitivity and setpoint philosophy intact. In a 3500 rack that already holds a 3500/72M Rod Position monitor and a 3500/77M Cylinder Pressure monitor, the Bently Nevada 3500/70M 136449-09 supplies the third leg of the reciprocating diagnostic stool: the frame and crosshead dynamics that neither rod position nor combustion pressure can see.
Technical Specifications
| Parameter | Value |
|---|---|
| Product Model | 3500/70M 136449-09 |
| Manufacturer | Bently Nevada (Baker Hughes) |
| Product Type | Reciprocating Impulse/Velocity Monitor (4-channel, full-height) |
| System Platform | Bently Nevada 3500 Series Machinery Protection System |
| Measurement Channels | 4 independent, programmed in pairs |
| Selectable Functions | Impulse Acceleration, Acceleration 2, Recip Velocity, Low-Frequency Recip Velocity |
| Compatible Transducers | 330500 / 330525 Velomitor®, 190501 Velomitor CT, 330400 / 330425 accelerometers, seismic velocity probes |
| Input Signal Count | 1 to 4 velocity or acceleration transducer signals |
| Input Impedance | 10 kΩ (acceleration input); >1 MΩ (velocity input) |
| Sensitivity, Impulse/Accel 2 | 0.51–11.72 mV/(m/s²), or 5–115 mV/g (100 mV/g nominal) |
| Sensitivity, Recip Velocity / LF Recip Velocity | 3.54–22.64 mV/(mm/s), or 90–575 mV/(in/s) |
| High-Pass Filter (Impulse/Accel) | 3–3000 Hz, 4-pole (24 dB/octave); RMS corner 10–3000 Hz |
| Low-Pass Filter (Impulse/Accel) | 30–30,000 Hz, 4-pole |
| High-Pass Filter (Recip Velocity) | 1–400 Hz, 4-pole; RMS corner selectable |
| Low-Pass Filter (Recip Velocity) | 40–5500 Hz, 4-pole |
| Not-OK Filter | 1-pole, −3 dB at 2400 Hz |
| Smoothing | 8-revolution running average |
| Signal Conditioning Accuracy | ±0.33% typical, ±1% maximum (filters excluded) |
| Transducer Supply | −22 Vdc minimum; 40 mA max per channel, 15 mA max at start-up |
| Supply Output Impedance | 20 Ω typical; 1000 Ω typical under foldback |
| Foldback Current | 15.4–24.9 mA |
| Special Inhibit Input | Contact closure, 5 Vdc @ 390 μA typical |
| Buffered Transducer Output | 4 front-panel coaxial (BNC), one per channel; 550 Ω typical, short-circuit protected |
| Recorder Output | +4 to +20 mA per channel, proportional to selected static value |
| Recorder Accuracy / Resolution | ±0.05 mA; ±0.14 mA over temperature; 0.3662 μA max resolution |
| Recorder Load / Compliance | 600 Ω maximum; +12 Vdc maximum compliance |
| Recorder Update Rate | <100 ms |
| Alarm Setpoints | Alert on every active static value; Danger on any two; 0–100% FS, ±0.13% accuracy |
| Alarm Delays | Alert 1–60 s; Danger 0.1–60 s |
| Front-Panel Indicators | OK, TX/RX, Bypass, plus four channel-status LEDs |
| Power Consumption | 7.7 W nominal from rack backplane |
| Rack Footprint | 1 full-height front slot + 1 full-height rear I/O slot |
| Module Dimensions | 241.3 mm × 24.4 mm × 241.8 mm (H × W × D) |
| Module Weight | 0.91 kg (rear I/O sub-module 0.20–0.46 kg) |
| Operating Temperature | −30 °C to +65 °C (0 °C to +65 °C for Internal Barrier I/O option) |
| Storage Temperature | −40 °C to +85 °C |
| Humidity | 5% to 95% RH, non-condensing |
| Agency / Compliance | CE, CSA, cNRTLus; ATEX / IECEx / CSA Zone 2 options; API 670 guidance |
| Direct Cross-Reference | 176449-09 (later/alternate PWA numbering for the same monitor family) |
