Official datasheet reference: 141535 Rev. R — Cordant 3500/40M Proximitor Monitor

In high-stakes rotating machinery environments — from thermal power turbine trains to oil and gas compressor lines — the difference between normal operation and catastrophic failure can be measured in microns. The Bently Nevada™ 3500/40M Proximitor Monitor is engineered to capture those microns with unwavering accuracy, delivering four channels of simultaneous vibration and position measurement within the 3500 Machinery Protection System.

One Monitor, Multiple Measurement Disciplines

The 3500/40M is not a single-purpose module. Each of its four channels can be independently programmed via the 3500 Rack Configuration Software to perform one of five critical functions:

• Radial Vibration — the cornerstone of rotor health assessment

• Thrust Position — axial displacement monitoring for rotor-to-stator clearance

• Differential Expansion — detecting thermal growth mismatches in large turbine casings

• Eccentricity — capturing slow-roll bow and runout conditions

• REBAM — bearing defect detection through spike, element, and rotor filtering

Channels are configured in pairs: channels 1 and 2 share one function, while channels 3 and 4 can perform either the same or a different function. This architecture allows a single 3500/40M to monitor, for example, radial vibration on two bearing planes while simultaneously tracking thrust position on the same machine train.

Signal Conditioning That Goes Beyond the Basics

Every channel accepts input directly from Bently Nevada proximity transducers — no external signal preconditioners required. The monitor conditions each signal to produce a suite of static values, each available for alert and danger setpoint configuration.

For radial vibration, the 3500/40M delivers a comprehensive parameter set: Direct and Gap measurements, 1X and 2X amplitude with phase lag, Not 1X amplitude, and Smax. The 1X and 2X vector filters employ a Constant Q design with a minimum stopband rejection of -57.7 dB, ensuring precise synchronous tracking even as machine speed varies. The Not 1X filter, with -34.9 dB minimum stopband rejection, isolates non-synchronous components that often signal developing faults.

Frequency response is user-programmable across multiple filter paths: a direct filter spanning 4 Hz to 4000 Hz or 1 Hz to 600 Hz, a gap filter with -3 dB corner at 0.09 Hz, and a Not 1X filter covering 60 cpm to 15.8 times running speed.

Accuracy You Can Defend

When a protection system trips a turbine, the measurement must be defensible. The 3500/40M delivers:

• Direct and Gap: ±0.33% of full-scale typical, ±1% maximum (exclusive of filtering)

• 1X and 2X: ±0.33% typical, ±1% maximum

• Smax: ±5% maximum

• Not 1X: ±3% for machine speeds below 30,000 cpm; ±8.5% above

Phase accuracy is held to a maximum of 3 degrees error. Alarm setpoints are adjustable from 0 to 100% of full-scale for each measured value, with accuracy within 0.13% of the desired value.

Thrust, Differential Expansion, and Eccentricity

For thrust and differential expansion measurements, the 3500/40M provides Direct and Gap static values with a direct filter response of -3 dB at 1.2 Hz and gap filter response of -3 dB at 0.41 Hz. Accuracy remains ±0.33% typical, ±1% maximum.

Eccentricity channels return Peak-to-Peak, Gap, Direct Minimum, and Direct Maximum values, with direct filter response at -3 dB at 15.6 Hz and gap filter response at -3 dB at 0.41 Hz.

REBAM: Bearing Health at the Speed of Sound

The REBAM channel type transforms the 3500/40M into a bearing defect detection instrument. It returns Spike, Element, Rotor, Direct, Gap, 1X Amplitude, and 1X Phase Lag static values. The spike filter is user-programmable from 0.152 Hz to 8678 Hz; element bandpass covers 0.139 Hz to 3836 Hz with a high-pass corner at 0.8x BPFO and low-pass corner at 2.2x BPFO; rotor filtering spans 0.108 Hz to 2221 Hz.

REBAM requires the M version of the 3500 Proximitor Monitor and specific firmware/software revisions: 3500/40M Module Firmware Revision 2.1, 3500/01 Software Version 3.30, 3500/02 Software Version 2.40, 3500/03 Software Version 1.40, and DM2000 Software Version 3.40.

Filter Tracking for Variable Speed Machines

When machine speed changes, filter parameters must follow. The 3500/40M implements automatic filter tracking with defined switching thresholds:

• Switch from nominal to lower filter set when current shaft speed ≤ 0.9 × nominal

• Switch from lower to nominal when current shaft speed ≥ 0.95 × nominal

• Switch from nominal to higher filter set when current shaft speed ≥ 1.1 × nominal

• Switch from higher to nominal when current shaft speed ≤ 1.05 × nominal

In the event of a shaft speed error condition, the monitor defaults to the nominal filter set, ensuring continued protection.

Outputs and Front Panel Indications

Each channel provides a buffered transducer output via a front-panel coaxial connector, short-circuit protected with 550 Ω output impedance. The transducer power supply delivers -24 Vdc.

Three front-panel LEDs provide immediate status: OK (proper operation), TX/RX (communication with other rack modules), and Bypass (monitor in bypass mode).

Environmental and Physical Resilience

The 3500/40M operates from -30°C to +65°C when used with Internal/External Termination I/O Modules, and 0°C to +65°C with Internal Barrier I/O Modules. Storage temperature ranges from -40°C to +85°C. Humidity tolerance is 95%, noncondensing.

The monitor module measures 241.3 mm × 24.4 mm × 241.8 mm and weighs 0.91 kg. Non-barrier I/O modules occupy 241.3 mm × 24.4 mm × 99.1 mm and weigh 0.20 kg; barrier I/O modules measure 241.3 mm × 24.4 mm × 163.1 mm and weigh 0.46 kg.

Hazardous Area Approvals

The 3500/40M carries comprehensive global approvals. For cNRTLus, when used with I/O modules without internal barriers, it is rated Class I, Zone 2: AEx/Ex nA nC ic IIC T4 GC; Class I, Division 2, Groups A, B, C, and D; T4 @ Ta = -20°C to +65°C. With internal barriers, the rating extends to include [ia Ga] intrinsic safety outputs for Division 1.

ATEX/IECEx approvals mirror these classifications, with the internal barrier version providing II 3(1) G Ex nA nC ic [ia Ga] IIC T4 Gc when installed per drawing 138547.

Compliance and Certifications

The 3500/40M complies with FCC Part 15, EMC Directive 2014/30/EU (EN 61000-6-2 and EN 61000-6-4), LV Directive 2014/35/EU (EN 61010-1), and RoHS Directive 2011/65/EU. China RoHS cables carry an EFUP designation of 15 years per SJ/T 11364-2024.

Ordering Information

The 3500/40M Proximitor Monitor is ordered as 3500/40M-AA-BB:

A: I/O Module Type

• 01: Proximitor I/O Module with Internal Termination

• 02: Proximitor I/O Module with External Terminations

• 03: Proximitor I/O Module with Internal Barriers and Internal Terminations

B: Hazardous Area Approval Option

• 00: None

• 01: cNRTLus (Class 1, Division 2)

• 02: ATEX / IECEx / CSA (Class 1, Zone 2) — only available with A-03

External Termination Blocks (125808-01 with Euro style connectors, 128015-01 with terminal strip connectors) and cables (129525-AAAA-BB) must be ordered separately when external terminations are specified.

The Bottom Line

The Bently Nevada 3500/40M Proximitor Monitor delivers four channels of high-accuracy, configurable protection for the most demanding rotating machinery applications. Whether monitoring radial vibration on a gas turbine, thrust position on a steam turbine, or bearing health via REBAM, it provides the measurement integrity, environmental robustness, and hazardous area certifications required for global deployment.