Bently Nevada 3500/70M Recip Impulse Velocity Monitor
Overview
The Bently Nevada 3500/70M Recip Impulse Velocity Monitor is a four-channel module for the Bently Nevada 3500 rack, built as part of the reciprocating compressor solutions package to watch crankcase and crosshead vibration. It accepts signals from seismic transducers, conditions them into vibration measurements, and compares the results with user-programmable alarms. Each channel pair can be set to one of four functions: Impulse Acceleration, Acceleration 2, Recip Velocity or Low Frequency Recip Velocity, so one Bently Nevada 3500/70M can cover frame velocity on two throws and crosshead impacts on two others.
Seven Star LLC supplies the Bently Nevada 3500/70M, its I/O modules and external termination hardware to compressor owners in the Sultanate of Oman and across the GCC, with engineering support in Muscat. The manufacturer datasheet (166766 Rev. T) is attached here, and our team can help map the I/O option and transducer mix to an existing or new compressor monitoring rack.
Measurement Principle
Reciprocating machines do not vibrate like turbomachinery. Their loads change sharply through every revolution, and faults such as loose piston rod nuts, worn crosshead pins or excessive running clearances show up as short impacts at particular crank angles. The Impulse Acceleration function of the Bently Nevada 3500/70M therefore provides six user-adjustable crank-angle bands, each with a start between 0 and 359° and a duration of 1 to 360° at 1° resolution, and reports peak or RMS acceleration inside each band, smoothed with an 8-revolution average. High-pass corners can be set from 3 to 3000 Hz and low-pass corners up to 30 kHz with 4-pole filters.
The velocity functions address the frame and crankcase, where low-frequency motion caused by imbalance, foundation problems or loose anchor bolts is the main concern. Recip Velocity and Low Frequency Recip Velocity integrate the sensor signal and return direct value, 1X and 2X amplitude and phase from a constant-Q vector filter with a bandwidth of ±3% of running speed, plus a bias voltage for diagnostics. The low-frequency version allows high-pass corners as low as 0.750 Hz. The standard lower limit for machine speed is 60 rpm; machines down to 30 rpm need modification 135M8137-01. Accuracy is within ±0.33% of full scale typical and ±1% maximum, not including filter effects.
Engineering Design of the Bently Nevada 3500/70M
The Bently Nevada 3500/70M takes one full-height front slot and one full-height rear slot. The front panel provides OK, TX/RX and Bypass LEDs and one short-circuit-protected coaxial buffered output per channel at 550 Ω typical impedance. The module powers its transducers at −22 Vdc minimum and up to 40 mA, with foldback protection between 15.4 and 24.9 mA, and draws 7.7 W nominal. A special inhibit contact input (5 Vdc at 390 µA typical) is also provided. Recorder outputs of +4 to +20 mA carry one selected static value per channel, with 600 Ω maximum load and an update rate below 100 ms.
Five I/O module options for the Bently Nevada 3500/70M cover the usual transducer arrangements: Prox/Velom I/O with internal or external terminations, and three internal-barrier versions for four accelerometers, two accelerometers with two Velomitor sensors, or four Velomitor sensors, for intrinsically safe connection to sensors mounted on compressor frames in hazardous areas. Alert setpoints can be placed on every static value and Danger setpoints on any two of them, with Danger delays down to 0.1 second nominal. The main board weighs 0.91 kg.
Key Features
The main functions of the Bently Nevada 3500/70M described in the manufacturer datasheet are:
- Four channels, programmed in pairs, with up to two different functions running at once.
- Impulse Acceleration with six crank-angle bands reporting peak or RMS acceleration.
- Recip Velocity and Low Frequency Recip Velocity with 1X and 2X amplitude and phase.
- Sensitivity ranges of 5 to 115 mV/g for acceleration and 90 to 575 mV/(in/s) for velocity.
- Internal barrier I/O options for accelerometer, Velomitor or mixed sensor sets.
- Short-circuit-protected buffered outputs and individual 4 to 20 mA recorder outputs.
- Danger alarming on any two static values per channel with delays down to 0.1 second.
- Marine classification to DNV GL and ABS rules, with cNRTLus, ATEX and IECEx options.
Industrial Applications
Reciprocating compressors are found throughout Oman’s upstream and midstream assets: gas lift and gas injection units, fuel gas boosters, hydrogen make-up compressors in refineries, and process gas compressors in petrochemical plants. The Bently Nevada 3500/70M is typically installed with velocity sensors on the crankcase and accelerometers on each crosshead guide, so that frame vibration and crosshead impacts are alarmed in the same rack. Within the reciprocating compressor package it can be paired with the Bently Nevada 3500/72M Recip Rod Position Monitor and the 3500/77M Recip Cylinder Pressure Monitor for a fuller picture of each throw.
Alarms from the Bently Nevada 3500/70M can drive relay cards such as the Bently Nevada 3500/32M 4-Channel Relay Module, while the 3500/22M Transient Data Interface passes waveform and static data to System 1 software; the datasheet calls for 3500/22M TDI firmware 1.75 or later. Speed and phase references come from the 3500/25 Keyphasor Module. Seven Star LLC supports compressor teams in Oman and the GCC with module selection, firmware checks and spares planning for Sohar, Duqm and Salalah facilities.
Ordering Information
The Bently Nevada 3500/70M is ordered as 3500/70M-AA-BB with the following options from the datasheet:
| Option | Code | Description |
|---|---|---|
| A: I/O Module Type | 01 | Prox/Velom I/O Module with Internal Terminations |
| A: I/O Module Type | 02 | Prox/Velom I/O Module with External Terminations |
| A: I/O Module Type | 03 | Internal Barrier, Four Accelerometers |
| A: I/O Module Type | 04 | Internal Barrier, Two Accelerometers, Two Velomitors |
| A: I/O Module Type | 05 | Internal Barrier, Four Velomitors |
| B: Agency Approval | 00 | None |
| B: Agency Approval | 01 | cNRTLus (Class 1, Division 2) |
| B: Agency Approval | 02 | ATEX/IECEx/CSA (Class 1, Zone 2) |
An Earthing Module must be ordered for each rack with internal barriers. Termination blocks, cables and spares for the Bently Nevada 3500/70M:
| Part Number | Description |
|---|---|
| 176449-09 | 3500/70M Recip Impulse Velocity Monitor |
| 140471-01 | Prox/Velom I/O Module with Internal Terminations |
| 140482-01 | Prox/Velom I/O Module with External Terminations |
| 135489-01 | I/O Module with Internal Barriers, Internal Terminations, 4 x Prox/Accel |
| 135489-02 | I/O Module with Internal Barriers, Internal Terminations, 2 x Prox/Accel and 2 x Velomitor |
| 135489-03 | I/O Module with Internal Barriers, Internal Terminations, 4 x Velomitor |
| 125808-08 / 128015-08 | Proximitor / Velomitor External Termination Block (Euro Style / Terminal Strip connectors) |
| 128702-01 / 128710-01 | Recorder External Termination Block (Euro Style / Terminal Strip connectors) |
| 129525-AAAA-BB | 3500 Transducer (XDCR) to External Termination (ET) Block Cable; AAAA 0005, 0007, 0010, 0025, 0050 or 0100 feet; BB 01 not assembled, 02 assembled |
| 129529-AAAA-BB | 3500 Recorder Output to External Termination (ET) Block Cable; same codes |
| 00561941 | 3500/70M Prox/Velom I/O Module ten-pin connector shunt |
| 00580434 / 00580432 / 00502133 | Internal I/O Module connector header, Euro Style, 8 / 10 / 12 pin |
| 166M2389 / 166M2388 | Connector header, push-in-spring type (alternatives for PN 00580434 / 00580432) |
| 166226-01 | 3500/70M Recip Impulse Velocity Monitor User Manual |
Technical Specifications
Key Bently Nevada 3500/70M data from datasheet 166766 Rev. T:
| Parameter | Specification |
|---|---|
| Model | Bently Nevada 3500/70M Recip Impulse Velocity Monitor |
| Channels / functions | 4, in pairs: Impulse Acceleration, Acceleration 2, Recip Velocity, Low Frequency Recip Velocity |
| Input impedance | 10 kΩ acceleration input; >1 MΩ velocity input |
| Sensitivity | Acceleration 0.51–11.72 mV/(m/s²) (5–115 mV/g); velocity 3.54–22.64 mV/(mm/s) (90–575 mV/(in/s)) |
| Accuracy | Within ±0.33% of full scale typical, ±1% maximum, not including filter effects |
| Impulse acceleration bands | Six bands; start 0–359°, duration 1–360°, 1° resolution; 8-revolution average |
| Vector filter | 1X and 2X, constant Q, bandwidth ±3% of running speed, Q = 16.7 |
| Machine speed | 60 rpm minimum standard; 30 rpm with modification 135M8137-01 |
| Transducer power | −22 Vdc minimum, 40 mA maximum, foldback 15.4–24.9 mA |
| Buffered outputs | One coaxial per channel, 550 Ω typical, short-circuit protected |
| Recorder outputs | +4 to +20 mA; +12 Vdc compliance maximum; 600 Ω maximum; within ±0.05 mA; update <100 ms |
| Alarm delays | Alert 1–60 s in 1 s steps; Danger 0.1 s nominal or 1–60 s in 1 s steps |
| Power consumption | 7.7 W nominal |
| Operating temperature | −30 to +65 °C (external termination I/O); 0 to +65 °C (internal barrier I/O) |
| Storage / humidity | −40 to +85 °C; 95% non-condensing |
| Main board dimensions / weight | 241.3 × 24.4 × 241.8 mm; 0.91 kg |
| Software / firmware | 3500/01 v5.2 or later; 3500/02 v2.50 or later; 3500/03 v1.50 or later; System 1 v6.90 or later; 3500/70M firmware 4.21 or later |
How to Order
To request a quotation for the Bently Nevada 3500/70M, send Seven Star LLC the full 3500/70M-AA-BB code, or the sensor arrangement on each compressor throw, the hazardous area classification and your rack software versions. Our team in Muscat will confirm availability, lead time and the termination hardware required, and the datasheet can be downloaded from the documents tab on this page. We supply the Bently Nevada 3500/70M to customers in Oman and the GCC.
- Datasheet Bently Nevada 3500/70M Recip Impulse Velocity Monitor Datasheet (166766 Rev. T) Download
Bently Nevada 3500 modules and transducers
The listed 3500 modules include the 3500/20 Rack Interface Module, the 3500/50M Tachometer, the 3500/61 Temperature and 3500/62 Process Variable monitors, the 3500/64M Dynamic Pressure monitor, the 3500/44M for aeroderivative gas turbines and the 3500/46M Hydro monitor. Reciprocating compressor monitoring is covered by the 3500/70M, 3500/72M and 3500/77M. The 3500/92 Communication Gateway and 3500/94M display link the rack to the control system. Transducers include the 3300 XL proximity probe system, the 330400 accelerometer and the 190501 Velomitor CT velocity transducer. The manufacturer's newer platform, Orbit 60, is offered as the modernization path for 3500 racks, and System 1 software handles diagnostics.Where Bently Nevada vibration monitoring is used
Steam and gas turbines, generators, centrifugal and reciprocating compressors, large pumps, hydro units and cooling tower fans in oil and gas, power generation, petrochemical and mining plants are the usual machines. Measurements include radial vibration, thrust position, speed, phase, differential expansion, bearing temperature, rod position and cylinder pressure.Ordering Bently Nevada parts: what we need
Send the complete part number with every option field, for example 330103-00-05-10-01-00 for a probe or the 3500 module number with its option dashes, plus the matching I/O module number. For probe systems state probe series, system length and the hazardous area approval. A photo of the label avoids transcription errors, and for rack modules the firmware revision is useful.Browse Bently Nevada products by category: Vibration.
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