Bently Nevada 3500/42 monitor module

Bently Nevada  3500/42  monitor module

I. Overview

3500/42 is the vibration monitoring module in the Bently Nevada 3500 series, focusing on the vibration state analysis 

of rotating machinery. Unlike the 350/40 module (which focuses on displacement parameters), its channel type takes 

vibration energy parameters as the core, and assesses equipment failures through signals such as acceleration, velocity,

 and absolute vibration. It is suitable for machinery sensitive to vibration, such as gearboxes, fans, and pumps.

Ii. Core Channel Types and Technical Analysis

1. Acceleration

Monitoring purpose: To measure the vibration acceleration of mechanical components (unit: g or m/s2), reflecting 

high-frequency vibration characteristics (such as bearing failure, gear meshing impact).

Sensor type:

Piezoelectric Accelerometer (Piezoelectric accelerometer) uses the piezoelectric effect to convert mechanical vibration 

into a charge signal, and the response frequency can reach over 10kHz;

IEPE (Integrated Electronic Piezoelectric) sensor: Built-in charge amplifier, output voltage signal (such as ±5V), strong 

anti-interference ability.

Measurement principle:

The sensor converts the acceleration signal into an electrical signal, which is filtered by the 3500/42 module (such as 

high-pass filtering to remove low-frequency noise) and amplified, and then outputs the peak value, effective value or 

time-domain waveform of the acceleration.

Key parameters:

Measurement range: 0-50g (customizable for higher ranges)

Frequency response: 1Hz to 10kHz (typical value)

Application scenarios: High-frequency fault diagnosis such as bearing outer rings and gear tooth surface damage.

2. Velocity

Monitoring purpose: To measure the vibration velocity of mechanical components (unit: mm/s or in/s), reflecting 

medium and low frequency vibration energy (such as rotor imbalance, mechanical loosening).

Sensor type:

Magnetoelectric Velocity sensor (Velocity Pickup) : It generates a voltage signal proportional to the velocity by the coil 

cutting the magnetic field lines, with a frequency response range of 10Hz to 1kHz.

Or it can be derived from the integration of acceleration signals (with an integrated circuit built into the 3500/42 

module).

Measurement principle:

The magnetoelectric sensor directly outputs the speed signal;

The acceleration signal is integrated once to obtain the velocity (time-domain integration or frequency-domain 

integration), and the module can eliminate the DC offset error.

Key parameters:

Measurement range: 0-250mm/s (effective value)

Industry standards: Vibration evaluation standards such as ISO 10816 take the effective value of velocity as the 

benchmark;

Application scenarios: Analysis of medium and low-frequency faults such as unbalanced motor rotors and loose 

foundations.

3. Absolute Shaft Vibration

Monitoring objective: To measure the absolute vibration of the rotor relative to a fixed reference frame (unit: μm or 

mil), comprehensively reflecting the superimposed effect of rotor vibration and bearing housing vibration, which is 

closer to the actual operating state than radial vibration (relative vibration).

Sensor type:

Combined sensor: Composed of an eddy current sensor (for measuring the relative vibration of the rotor) and an 

acceleration sensor (for measuring the absolute vibration of the bearing housing), the absolute vibration is calculated 

through the vector summation function of the 3500/42 module.

Or directly use a non-contact absolute vibration sensor (such as a laser Doppler vibrometer, which requires additional 

configuration).

Measurement principle:

The eddy current sensor acquires the displacement signal (relative vibration) of the rotor relative to the bearing.

The acceleration sensor acquires the absolute vibration velocity signal of the bearing housing and converts it into 

displacement through integration.

The module calculates through phase synchronization and superimposes the vectors of the two to obtain the absolute

vibration displacement of the shaft (peak-to-peak value or RMS value).

Key parameters:

Measurement range: 0-500μm (peak-to-peak value)

Phase accuracy: Error ≤5°, ensuring the accuracy of vector synthesis;

Application scenarios: Full-state vibration assessment of large rotating machinery such as steam turbines and 

compressors to avoid monitoring errors caused by bearing housing vibration.

Iii. Technical Characteristics of the 3500/42 Module

Signal processing function:

It is equipped with multi-order filtering (low-pass, high-pass, band-pass), which can screen signals based on the fault 

frequency range (such as bearing fault characteristic frequencies BPFI, BPFO).

Supports FFT spectrum analysis, outputs vibration spectrum diagrams, and locates the main vibration frequency (such

 as 1X, 2X rotational speed frequencies).

Configuration and Output:

Each module typically supports 4 to 8 channels and can be independently configured as acceleration, velocity or 

absolute vibration modes.

Output signal: 4~20mA (engineering value), ±10V (original signal), compatible with PLC/DCS systems and portable 

vibration analyzers.

Fault diagnosis support:

Calculate the characteristic parameters such as vibration Velocity (RMS) and Kurtosis in real time to identify early faults;

Support trend analysis, draw vibration amplitude-time curves through historical data, and predict the deterioration 

trend of equipment.

Iv. Precautions for Project Implementation

Sensor installation:

The acceleration sensor needs to be rigidly fixed (such as by magnetic attraction or bolt installation) to avoid 

resonance affecting the measurement.

When measuring absolute vibration, the installation positions of the eddy current and acceleration sensors should be 

close (≤50mm) to ensure phase consistency.

Parameter configuration:

The acceleration channel needs to be set with an appropriate high-pass filtering frequency (such as 10Hz, to filter out 

mechanical low-frequency jitter).

The absolute vibration channel needs to calibrate the phase difference between the eddy current and the acceleration 

signal (usually adjusted through on-site dynamic balance tests).

Standard reference:

Vibration evaluation refers to specifications such as ISO 10816 (speed) and API 670 (Requirements for Mechanical 

Protection systems), and the alarm/shutdown threshold is set.

The 3500/42 module provides a complete solution from fault early warning to condition assessment for rotating 

machinery through multi-dimensional vibration parameter monitoring, especially having irreplaceable advantages in 

high-frequency fault diagnosis and absolute vibration analysis. In practical applications, it is necessary to rationally 

select the channel type and sensor configuration in combination with the equipment type and fault mechanism to 

achieve precise monitoring and protection.