Bently Nevada 330425 Accelerometer Acceleration Transducer

The Bently Nevada 330425 is a high‑range piezoelectric accelerometer designed for critical machinery monitoring applications where casing acceleration measurements may exceed the capabilities of standard 50 g sensors. This transducer is specifically engineered to meet the requirements of American Petroleum Institute (API) Standard 670 for accelerometers, providing a 75 g peak amplitude range with a sensitivity of 25 mV/g. It is the higher‑amplitude sibling of the widely used 330400 series, sharing the same mechanical dimensions, rugged construction, and environmental sealing, but offering a lower sensitivity to accommodate larger vibration signals without saturation.

The 330425 is intended for machinery with inherently higher vibration levels, such as high‑speed gearboxes, reciprocating compressors, certain turbine stages, and equipment operating under severe mechanical stress. Its extended amplitude range (50% higher than the 330400) ensures that transient spikes or continuous high‑amplitude vibrations are accurately measured without clipping, while its robust piezoelectric sensing element and internal charge amplifier deliver reliable, low‑impedance voltage output for monitoring and protection systems.

Like its 330400 counterpart, the 330425 is available with either a ¼‑28 UNF or M8 x 1 integral mounting stud, and with a range of agency approval options (including ‑00 for non‑hazardous areas, ‑05 for multiple international hazardous area certifications, and ‑CN for Chinese GB/T 3836 certification). This flexibility allows the sensor to be deployed in both safe and classified locations worldwide, making it a versatile choice for new installations and retrofit projects.

The transducer features a case‑isolated design to prevent ground loops, a hermetically sealed stainless steel housing rated IP68, and a wide operating temperature range from ‑55°C to +121°C. It is built to withstand harsh industrial environments, including 100% condensing humidity, high shock loads (5000 g peak), and magnetic fields up to 50 gauss. With its 3‑pin MIL‑C‑5015 connector and compatibility with standard Bently Nevada cables, the 330425 integrates seamlessly into existing vibration monitoring systems.

This product introduction focuses on the Bently Nevada 330425 series, highlighting its unique high‑range characteristics, comparing it with the 330400, and detailing its available configurations, specifications, and application fit.

Functional Description and High‑Amplitude Capability

The 330425 accelerometer operates on the piezoelectric principle, where a piezoelectric element generates an electrical charge proportional to the applied acceleration. This charge is converted by an internal charge amplifier into a low‑impedance voltage signal that is transmitted via the output cable to the monitoring system. The key differentiator of the 330425 is its sensitivity of 25 mV/g (2.5 mV/m/s²) and its 75 g peak acceleration range, compared to the 330400's 100 mV/g and 50 g range.

The lower sensitivity is a deliberate trade‑off: it reduces the output voltage per unit of acceleration, allowing the sensor to measure higher peak amplitudes without saturating the amplifier or exceeding the linear range of the monitoring system. For machinery where vibration levels frequently exceed 50 g, such as high‑speed gearboxes with gear mesh excitation, reciprocating compressors with strong impacts, or turbines with blade pass frequencies, the 330425 provides a reliable measurement without the risk of clipping or distortion.

The amplitude linearity of ±1% up to 75 g peak ensures that the output is proportional to the input over the entire operating range. The frequency response is identical to the 330400: 10 Hz to 15 kHz (±3 dB) and 30 Hz to 10 kHz (±10%), covering most machinery vibration components, including gear mesh, blade pass, and bearing defects. The noise floor is slightly higher due to the lower sensitivity, but it remains adequate for most industrial applications; the datasheet does not specify a noise floor for the 330425, but it is proportionally higher than the 330400’s 0.004 g rms.

The 330425 shares the same mechanical footprint as the 330400, including the 23 mm diameter, 59 mm height (including stud), 99 g weight, and 3‑pin MIL‑C‑5015 connector. It uses the same mounting torque (4.1 N·m), the same base strain sensitivity characteristics, and the same cable options. This mechanical interchangeability allows users to upgrade from a 330400 to a 330425 without changing mounting hardware or cabling, provided the vibration levels justify the change.

Comparison with Bently Nevada 330400 – When to Choose 330425

To assist in proper sensor selection, the following table compares the Bently Nevada 330425 with its lower‑range sibling, the 330400, across key performance and application parameters.

Choose the 330425 when:

• Expected peak vibration amplitudes exceed 50 g.

• You are monitoring high‑speed gearboxes with gear mesh forces that produce high‑frequency, high‑amplitude signals.

• The machinery operates in reciprocating or impact‑prone environments.

• You require a sensor that can handle transient spikes without saturation.

• The lower sensitivity is acceptable because signals are sufficiently strong.

Choose the 330400 when:

• Expected vibration levels are consistently below 50 g.

• High sensitivity (100 mV/g) is needed to detect low‑amplitude bearing defects or early‑stage faults.

• You want a better signal‑to‑noise ratio for low‑amplitude measurements.

Available Configurations – Thread and Approval Options

The Bently Nevada 330425 is offered with the same mounting thread and agency approval combinations as the 330400, allowing customization for different mechanical and regulatory requirements.

Mounting Thread Options

Agency Approval Options

Thus, typical orderable configurations include:

• 330425-01-00 – ¼‑28 UNF, non‑hazardous

• 330425-02-00 – M8 x 1, non‑hazardous

• 330425-01-05 – ¼‑28 UNF, hazardous area approved (ATEX/IECEx/CSA)

• 330425-02-05 – M8 x 1, hazardous area approved (available as custom order)

• 330425-01-CN – ¼‑28 UNF, Chinese certified

• 330425-02-CN – M8 x 1, Chinese certified (custom)

The -05 and -CN certifications carry the same entity parameters (Ui=28 V, Ii=150 mA, Pi=0.84 W, Ci=10.8 nF, Li=0 μH) as the 330400, ensuring compatibility with intrinsic safety barriers.

Hardware Characteristics – Specific to 330425 (All Configurations)

Physical Dimensions and Mounting

• Diameter: 23 mm (0.93 in)

• Height: 59 mm (2.3 in) including stud

• Weight: 99 g (3.5 oz) typical (no cable)

• Mounting Surface Finish: 32 µin rms or better

• Mounting Torque: 4.1 N·m (3.0 ft·lb)

• Thread Options: ¼‑28 UNF or M8 x 1, integral stud

Connector and Cabling

• Connector: 3‑pin MIL‑C‑5015 receptacle (316L stainless steel)

• Compatible Cables: 130539 (18 AWG with boot), 169253 (22 AWG), 167103 (22 AWG armored)

• Maximum Cable Length: 305 metres (1000 ft) – derated for intrinsic safety in hazardous areas

• Mating Connector: 00531080 for custom assemblies

Environmental and Electrical Specifications

• Power: -24 V dc ±0.5 V, 2 mA nominal bias current

• Output Bias Voltage: -8.5 V dc ±0.5 V

• Grounding: Case isolated

• Operating/Storage Temperature: -55°C to +121°C (-67°F to +250°F)

• Shock Survivability: 5000 g peak

• Relative Humidity: 100% condensing (hermetically sealed)

• IP Rating: IP68 (sensor only)

• Magnetic Field Susceptibility: < 225 mg/gauss at 50 gauss, 50‑60 Hz

• Maximum Altitude: 2000 m

• Outdoor Use: Standard in protected enclosure; optional splash boots

Base Strain Sensitivity

• For serial numbers beginning with “G” (newer production): 0.005 g/mstrain – no mounting base required.

• For serial numbers NOT beginning with “G” (older units): 0.100 g/mstrain without base; reduces to 0.0005 g/mstrain with Mounting Base (API adapter) – part numbers 37439-01 (¼‑28 to ¼‑28) or 37439-02 (M8 to M8).

Application Guidelines for 330425

The 330425 is recommended for machinery where peak vibration levels commonly exceed 50 g. Typical applications include:

• High‑Speed Gearboxes – Gear mesh forces can produce high‑amplitude, high‑frequency vibrations that may saturate a 50 g sensor. The 330425 provides ample headroom.

• Reciprocating Compressors – Impact forces from piston motion and valve operation generate high g‑levels; the 75 g range ensures accurate capture of these transients.

• Turbine Blade Pass Frequencies – In certain turbine stages, blade pass vibrations can be high in amplitude, especially under off‑design conditions.

• Heavy‑Duty Industrial Fans and Blowers – Large imbalance or aerodynamic forces can produce high casing accelerations.

• Testing and Commissioning – When vibration levels are unknown or expected to be high, the 330425 offers a safer margin.

For low‑amplitude bearing fault detection or general machinery monitoring where vibration is moderate, the 330400 with its higher sensitivity (100 mV/g) is preferred. The 330425 should be selected when there is a risk of over‑range with a 50 g sensor.

Installation Best Practices (Applicable to All 330425 Variants)

1. Surface Preparation – Clean and lap the mounting surface to 32 µin rms or better to ensure optimal mechanical coupling.

2. Stud Installation – Apply anti‑seize if needed, hand‑tighten, then torque to 4.1 N·m (3.0 ft·lb). Use the stud flats, not the connector body, for torque.

3. Cable Connection – Use recommended cables (130539, 169253, or 167103) and route away from high‑voltage lines. For hazardous areas, ensure cable parameters meet intrinsic safety limits.

4. Grounding – The case is isolated, so ground the cable shield at the power supply end only to avoid ground loops.

5. Base Strain – For older sensors (non‑G serial numbers), install the appropriate Mounting Base (37439‑01 or 37439‑02) to reduce base strain sensitivity.

6. Environmental Protection – Use splash boots and conduit for outdoor or wet installations.

Ordering Information and Accessories

Ordering Part Number Structure

330425-AA-BB or 330425-AA-CN:

• AA = Mounting Thread: 01 (¼‑28 UNF), 02 (M8 x 1)

• BB = Approval: 00 (None), 05 (Multiple international), CN (China)

Compatible Cables

Accessories

Certifications and Compliance

The 330425 carries the same certifications as the 330400, including:

• FCC Part 15 – Radio frequency interference limits.

• EMC Directive 2014/30/EU – Electromagnetic compatibility.

• RoHS Directive 2011/65/EU – Restriction of hazardous substances.

• China RoHS – EFUP of 15 years (SJ/T 11364‑2024).

• ATEX Directive 2014/34/EU (with -05 option).

• IECEx (with -05 option).

• CSA (with -05 option) for North American hazardous locations.

• ABS (with -05 option) for marine/offshore applications.

• GB/T 3836 (with -CN option) for Chinese hazardous locations.

Warranty and Support

The Bently Nevada 330425 is covered under the standard manufacturer’s warranty. For technical support, application engineering, or ordering assistance, contact your local Bently Nevada representative or access the Bently Nevada Media Library at bntechsupport.com.