When a rotating machine needs vibration monitoring, the first decision is usually which Bently Nevada platform fits the job. The two most common choices are the 3500 Series (the API 670 modular rack) and the 1900/65A (a compact standalone monitor). This comparison explains the difference so you can pick the right one without overspending or under-protecting your asset.
At a Glance: The Short Answer
Choose the 3500 Series for critical turbomachinery — turbines, large compressors and generators that need API 670 compliance, SIL-rated protection and integration with a DCS. Choose the 1900/65A for non-critical balance-of-plant machines — pumps, fans and small motors where a simple, low-cost 4–20 mA or Modbus output is enough.
Side-by-Side Comparison
| Feature | 3500 Series (Rack) | 1900/65A (Standalone) |
|---|---|---|
| Architecture | Modular rack, expandable | Fixed 6-channel unit |
| Channel count | 4 per monitor module, scale by adding cards | 6 (fixed) |
| Standard | API 670 machinery protection | General-purpose monitoring |
| Safety rating | SIL 2/3 capable | Not SIL-rated |
| Outputs | Modbus, Ethernet, buffered signals | 4–20 mA, Modbus RTU, Ethernet |
| Power | Rack supply, redundant option | 24 VDC nominal |
| Probe compatibility | 3300 XL 5 mm / 8 mm / 11 mm | 3300 XL 5 mm / 8 mm |
| Best for | Turbines, compressors, generators | Pumps, fans, small motors |
The 3500 Series: Modular Protection for Critical Machines
The 3500 Series is built as a rack of half-height modules, each performing a dedicated function. A complete system is assembled from these building blocks:
- 3500/42M Proximitor/Seismic Monitor — the 4-channel core monitor for radial vibration, axial position and differential expansion. It has a 10 Hz to 10 kHz bandwidth, ±0.5% accuracy and SIL 2/3 capability.
- 3500/15 Power Supply — the rack supply (85–264 VAC / 88–140 VDC input, +24 VDC output), with dual-redundant support.
- 3500/22M TDI — the communication gateway exporting data over Modbus TCP/RTU, Ethernet and OPC to DCS or System 1 software.
- 3500/25 Keyphasor — the once-per-revolution phase reference for speed (1–20,000 RPM) and orbit/balancing analysis.
Because it is modular, the 3500 scales from a single four-channel machine to a full turbine train with dozens of channels — all under one API 670-compliant architecture. This is why it is the reference system for power-generation turbines, LNG compressors and other safety-critical rotating equipment.
The 1900/65A: Compact Monitoring for Balance-of-Plant
The 1900/65A General Purpose Monitor is a 6-channel, fixed-configuration monitor designed for machines that do not justify a full rack. It accepts 3300 XL 8 mm and 5 mm probes and provides simple 4–20 mA, Modbus RTU and Ethernet outputs. It runs on 24 VDC and is a fraction of the cost of a 3500 system.
The trade-off is capability: no API 670 compliance, no SIL rating, no per-channel buffered outputs, and a fixed six-channel limit. For a balance-of-plant pump or fan where the requirement is simply "detect a problem and alarm", that is exactly the right level of protection.
Choosing the Right Probes
Both platforms use the same 3300 XL eddy-current probes, so the sensor selection is independent of the monitor:
- 3300 XL 8 mm — standard shaft vibration and position (0.5–4.0 mm linear range).
- 3300 XL 5 mm — miniature probe for tight mounting spaces (0.25–1.5 mm).
- TK-3E — compact 3 mm probe for case vibration on smaller machines.
Decision Guide: Which One Do You Need?
- Is the machine API 670 / safety-critical? → 3500 Series.
- Do you need SIL-rated protection? → 3500 Series (3500/42M is SIL 2/3 capable).
- Do you need more than 6 channels, or future expansion? → 3500 Series.
- Is it a pump, fan or small motor with a simple alarm requirement? → 1900/65A.
- Do you need phase reference and orbit analysis? → 3500 Series with 3500/25 Keyphasor.
Get a Quote
Glorient supplies both Bently Nevada platforms — the full 3500 Series rack and the 1900/65A — together with 3300 XL probes. Send us your machine list and required channels and our engineers will recommend the correct configuration. Request a quotation and we will respond within 24 hours.