Rotating machinery — turbines, compressors, pumps, generators and fans — is the beating heart of power plants, refineries and process facilities. When a bearing degrades or a shaft begins to whirl, the first warning signs show up as vibration and shaft position changes long before a failure. The Bently Nevada 3500 Series is the industry-standard machinery protection and condition monitoring platform for capturing those signals. This guide explains how to select the right 3500 Series modules and probes for your application, following the requirements of API 670 (Machinery Protection Systems).
1. What Is the Bently Nevada 3500 Series?
The 3500 Series is a modular, rack-based monitoring system built around a backplane that accepts half-height and full-height cards. A complete system is assembled from three building blocks: a monitor module that reads the sensors, a power supply that feeds the rack, and a communication module that exports data to DCS, PLC or condition-monitoring software. The sensing elements — eddy-current proximity probes — are mounted on the machine itself.
Because the platform is modular, you only buy the channels and functions you actually need. The sections below walk through each module so you can size a rack correctly.
2. The Core Monitor: 3500/42M Proximitor/Seismic Monitor
The Bently Nevada 3500/42M Proximitor/Seismic Monitor is the heart of most 3500 racks. It is a 4-channel module that accepts proximity probes and seismic transducers, delivering radial vibration, axial (thrust) position and differential expansion measurements for API 670 turbomachinery protection. Key specifications include a 10 Hz to 10 kHz bandwidth, ±0.5% accuracy, SIL 2/3 capability and compatibility with 3300 XL 5 mm, 8 mm and 11 mm probes.
Use the 3500/42M whenever you must protect a critical machine with vibration and position channels — it is the default choice for turbine, compressor and large pump trains. For a multi-channel rack, install one 3500/42M per four measurement points.
3. Powering the Rack: 3500/15 Power Supply Module
Every 3500 rack needs a regulated supply, and the 3500/15 Power Supply Module provides it. The module accepts a wide 85–264 VAC (or 88–140 VDC) input and produces a regulated +24 VDC output rated at 75 W continuous. It is a half-height module, and the rack supports dual redundant supplies — two 3500/15 modules can be fitted so that the loss of one does not interrupt monitoring.
For critical, continuously monitored machinery, specify the redundant configuration. For a standalone monitor with a single power source, a single 3500/15 is sufficient.
4. Data Communication: 3500/22M Transient Data Interface (TDI)
Raw vibration data is only useful if it reaches your control or maintenance system. The 3500/22M Transient Data Interface (TDI) is the communication gateway between the 3500 rack and the outside world. It supports Modbus TCP, Modbus RTU and Ethernet, plus OPC, and buffers 32 MB of static and 4 MB of transient waveform data. It is configured through the 3500 Configuration Software and typically integrates with Bently Nevada System 1 condition-monitoring software.
Add the 3500/22M whenever you need to export real-time values and transient waveforms to a DCS, historian or CM platform. For a machine that must be trended and diagnosed remotely, this module is essential.
5. Phase Reference: 3500/25 Enhanced Keyphasor Module
Vibration amplitude tells you how much a shaft is moving; the Keyphasor tells you where it is in its rotation. The 3500/25 Enhanced Keyphasor Module conditions the once-per-revolution reference signal from a proximity or magnetic pickup, providing shaft rotational speed (1 to 20,000 RPM) and phase reference for balancing, orbit analysis and diagnostics. It offers two input channels and is SIL-capable.
A Keyphasor is mandatory for any machine where you need phase-locked vibration analysis, such as unbalance diagnosis, rotor-to-stator rub detection or synchronous vibration trending.
6. The Sensing Element: 3300 XL Proximity Probes (8 mm and 5 mm)
The sensors that actually touch the measurement are the 3300 XL eddy-current proximity probes. Two diameters cover most applications:
- 3300 XL 8 mm Proximity Probe — the industry standard for shaft vibration and position. It has a 0.5–4.0 mm (80 mil) linear range and 7.87 V/mm (200 mV/mil) sensitivity, and operates from −55 °C to +177 °C.
- 3300 XL 5 mm Miniature Proximity Probe — a compact 5 mm probe for tight installation spaces, with a 0.25–1.5 mm (60 mil) linear range and the same electrical interface as the 8 mm version.
Choose the 8 mm probe for standard shaft measurements; switch to the 5 mm probe when physical clearance or mounting space is limited. Both connect directly to the 3500/42M monitor.
7. Standalone Monitoring: 1900/65A General Purpose Monitor
Not every machine justifies a full 3500 rack. The 1900/65A General Purpose Monitor is a 6-channel vibration monitor for non-critical rotating equipment such as fans, pumps and motors. It accepts 3300 XL 5 mm and 8 mm probes and outputs 4–20 mA, Modbus RTU and Ethernet signals. It runs on a simple 24 VDC supply and is a cost-effective alternative to the 3500 for balance-of-plant machines.
8. Compact Probes: TK-3E Eddy-Current Probe
For case vibration monitoring on smaller rotating equipment, the TK-3E Eddy-Current Probe offers a 3 mm tip in a compact package. It covers 10 Hz to 10 kHz with roughly 4 V/mm sensitivity and works from −20 °C to +120 °C — ideal for tight installations where a full 3300 XL assembly is overkill.
9. Selection Checklist
- Criticality — API 670 / SIL-rated machines use the 3500 Series; balance-of-plant machines can use the 1900/65A.
- Channels — count radial vibration, thrust position and differential expansion points; each 3500/42M provides 4.
- Power — specify one 3500/15, or two for redundancy.
- Communication — add a 3500/22M TDI for Modbus/OPC export.
- Phase — add a 3500/25 Keyphasor for speed and phase reference.
- Probes — select 3300 XL 8 mm or 5 mm based on clearance; use TK-3E for compact case-vibration needs.
10. Get a Quote
Glorient supplies genuine Bently Nevada 3500 Series modules and 3300 XL probes with datasheet, competitive pricing and global delivery. Send us your machine list and required channels and our engineers will confirm the correct rack configuration. Request a quotation and we will respond within 24 hours.