Bently Nevada 330500-03-00 Velomitor Piezo-velocity Sensor

The Bently Nevada 330500-03-00 is a specialized configuration of the industry‑standard 330500 Velomitor Piezo‑velocity Sensor, engineered for critical machinery monitoring in non‑hazardous (safe) areas where a fine‑thread mounting standard is preferred, featuring a factory‑installed 1/4‑28 UNF thread adapter for compatibility with precision mounting hardware. This variant carries no agency approvals (suffix -00) and is equipped with a 1/4‑28 UNF mounting adapter (suffix -03), making it the ideal choice for installations where space is limited, where fine‑thread adjustments are required, or where compatibility with existing 1/4‑28 UNF mounting bases (such as magnetic bases and certain accelerometer mounts) is essential, while explosion protection is not required.

The 330500 series is a state‑of‑the‑art piezoelectric velocity sensor with embedded integrated electronics, designed to measure absolute (relative to free space) bearing housing, casing, or structural vibration on rotating machinery. Unlike traditional velocity transducers that rely on moving coils and mechanical springs, the 330500 employs a solid‑state design with no moving parts, offering superior reliability, extended service life, and the ability to be mounted in any orientation—vertically, horizontally, or at any angle—without performance degradation.

The 330500-03-00 provides a velocity output of 100 mV/in/s (3.94 mV/mm/s) with a frequency response from 4.5 Hz to 5 kHz (±3 dB) and a velocity range of 50 in/s peak (1270 mm/s) . Its robust construction includes a hermetically sealed 316L stainless steel case, a 2‑pin MIL‑C‑5015 connector, and a wide operating temperature range from -55°C to +121°C. The sensor is case‑isolated to prevent ground loops, and it offers excellent immunity to magnetic fields and base strain. The -03-00 variant is supplied with a 1/4‑28 UNF adapter already threaded onto the body, ready for immediate installation using standard 1/4‑28 mounting hardware, without the need for separate adapter procurement or installation.

This introduction focuses exclusively on the 330500-03-00 configuration, highlighting its unique value as the fine‑thread, non‑certified Velomitor for safe‑area applications where 1/4‑28 UNF mounting is preferred. It compares this variant with other adapter options (e.g., -00-00 with no adapter, -01-00 with 1/2‑20 UNF, -02-00 with M8 x 1) and with certified fine‑thread versions (e.g., -03-01 with CSA, -03-02 with ATEX) to guide proper selection for non‑hazardous installations where fine‑thread mounting and performance are paramount.

Functional Description and the Advantage of 1/4‑28 UNF Fine‑Thread Mounting

The 330500-03-00 accelerometer operates on the piezoelectric principle, where a piezoelectric crystal generates an electrical charge proportional to the acceleration of the sensor housing. An internal charge amplifier and integrator circuit convert this acceleration signal into a velocity signal, which is then output as a low‑impedance voltage. The output bias voltage is nominally -12 V dc (referenced to Pin A), which allows the sensor to be powered by the same two‑wire interface used for many industrial monitoring systems. The sensor requires a power supply of -24 V dc (nominal) and draws a bias current of 2 mA (typical), with the dynamic signal superimposed on the bias voltage.

The integration of the electronics within the sensor housing eliminates the need for external signal conditioning, simplifies installation, and reduces the risk of noise pickup. The solid‑state design ensures that there are no moving parts to wear out, providing long‑term stability and repeatability. The 330500-03-00 is designed to be mounted directly on the machine casing or bearing housing using the supplied adapter. The 1/4‑28 UNF thread is a fine‑pitch thread (28 threads per inch) that is widely used in the vibration monitoring industry, particularly for magnetic bases (part number 46000‑01) and other accelerometer mounting hardware that requires a fine thread for precise adjustment and secure locking. The 1/4‑28 UNF thread is also a common standard for many accelerometers, making it a natural choice for retrofitting or replacing existing sensors without changing mounting hardware. The fine pitch offers excellent vibration resistance and allows for more precise torque control compared to coarse threads.

The -00 suffix indicates no hazardous area approvals, so the sensor is certified only for general industrial use (FCC, EMC, RoHS, China RoHS, and ABS for marine). This makes it the economical choice for safe areas where explosion protection is not required, and where the fine 1/4‑28 UNF thread is desired for compatibility with existing mounting hardware.

The sensor’s frequency response covers the range from 4.5 Hz to 5 kHz (270 cpm to 300,000 cpm) within ±3 dB, and from 6.0 Hz to 2.5 kHz (360 cpm to 150,000 cpm) within ±0.9 dB. This wide bandwidth makes it suitable for both low‑speed and high‑speed machinery, including gearboxes and turbines with high blade‑pass frequencies. The velocity output is particularly advantageous for machinery protection because it provides a direct measure of vibration severity, which is often the parameter used in international standards (e.g., ISO 10816) for evaluating machine health.

The sensor's amplitude linearity is ±2% up to 6 in/s peak, and its transverse sensitivity is less than 5% of the axial sensitivity. The mounted resonant frequency exceeds 12 kHz, ensuring that the sensor's natural resonance does not interfere with the measurement band. The case‑isolated design prevents ground loops, and the hermetically sealed construction protects the electronics from moisture and contaminants.

Detailed Comparison with Other 330500 Configurations – Adapter and Approval Options

To assist in proper sensor selection, the following table compares the 330500-03-00 with other common configurations: the 330500-00-00 (no adapter, no approvals), the 330500-01-00 (1/2‑20 UNF adapter, no approvals), the 330500-02-00 (M8 x 1 adapter, no approvals), and the 330500-03-01 (1/4‑28 UNF adapter, CSA). This comparison highlights the unique value of the -03-00 for fine‑thread, safe‑area applications.

Selection Guide – Key Differences

The 330500-03-00 is the most convenient fine‑threaded, non‑certified configuration for users who want a ready‑to‑mount 1/4‑28 UNF adapter. Choose this variant when:

• You need a velocity sensor for a non‑hazardous (safe) area.

• You prefer the 1/4‑28 UNF thread for compatibility with magnetic bases, compact mounts, or existing fine‑thread hardware.

• You want to avoid the hassle of sourcing and installing a separate adapter.

• You do not require explosion‑proof or intrinsic safety certifications.

If you need a different adapter (e.g., 1/2‑20 for coarse imperial, M8 for metric), choose the corresponding -01 or -02 option. If you require hazardous area approvals with fine thread, choose -03-01 (CSA) or -03-02 (ATEX).

Hardware Characteristics – Specific to 330500-03-00

Physical Dimensions and Mounting

• Adapter Thread: 1/4‑28 UNF (male), installed on the sensor body. The adapter is made of stainless steel and is factory‑torqued for reliable performance.

• Sensor Body Thread (under adapter): 3/8‑24 UNF‑2B (factory default).

• Height (with adapter): 63.2 mm (2.49 in) + additional height for the adapter (approx. 4‑6 mm, total ~67‑69 mm). The exact total height is not specified but the adapter adds minimal length.

• Diameter: 25.3 mm (0.995 in)

• Weight: 142 grams (5.0 oz) typical (without adapter); with adapter, slightly heavier.

• Case Material: 316L stainless steel, hermetically sealed

• Connector: 2‑pin MIL‑C‑5015 hermetically sealed receptacle, 316L stainless steel shell

• Mounting Torque for Adapter: 32‑46 kg·cm (24‑40 in‑lb) maximum (torque applied to the adapter when mounting the sensor onto the machine).

Polarity and Wiring

The sensor has a 2‑pin connector. The pin assignment is:

• Pin A: Signal + (positive output when the sensor case moves toward the connector)

• Pin B: Common (return) and power supply negative (shield)

The output bias voltage is -12 V dc (±3 V) referenced to Pin A. The sensor requires a -24 V dc supply (nominal) with a bias current of 2 mA (typical). The dynamic signal is a velocity output superimposed on the bias voltage.

Cables and Maximum Length

The 330500-03-00 is compatible with the same two‑conductor shielded cables as all 330500 variants. The recommended cable (part number 02173006) is 18 AWG twisted shielded bulk cable. For pre‑terminated cables, the following options are available (custom lengths in 1.0 ft increments):

Maximum cable length: 305 meters (1,000 ft) of cable (part number 02173006) with no signal degradation, provided the cable capacitance is within limits. For longer lengths, contact Bently Nevada Tech Support. The recommended cable length for a 50 g vibration at 10 kHz and cable capacitance of 200 pF/m is 208 ft (63 m).

Environmental and Electrical Specifications

• Power Requirements: -24 V dc nominal, 2 mA bias current typical

• Output Bias Voltage: -12 V dc ±3 V

• Dynamic Output Impedance: < 2400 Ω

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

• Shock Survivability: 5,000 g peak maximum

• Relative Humidity: 100% condensing (non‑submerged); case is hermetically sealed

• Base Strain Sensitivity: 0.005 in/s/mstrain (very low, minimising errors from mounting surface flexure)

• Magnetic Field Susceptibility: < 51 in/s/gauss at 50 gauss, 50‑60 Hz

• Grounding: Case isolated (housing isolated from signal common)

Application Guidelines – When to Use 330500-03-00

The 330500-03-00 is recommended for machinery monitoring applications where:

• The sensor will be installed in a non‑hazardous (safe) area.

• Direct velocity output is required for compatibility with monitoring systems.

• The mounting solution benefits from the 1/4‑28 UNF fine thread, which is compatible with magnetic bases (46000‑01), compact accelerometer mounts, and many existing installations.

• The user prefers a pre‑installed adapter to save time and avoid ordering separate parts.

• Space is limited or fine‑thread adjustment is required for precise sensor positioning.

Typical machinery applications include:

• Gas turbines and steam turbines (casing vibration)

• Centrifugal and reciprocating compressors

• Industrial fans, blowers, and pumps

• Gearboxes and high‑speed rotating equipment

• Generators and motors

• Portable or temporary monitoring setups using magnetic bases

When to choose a different configuration:

• If you need a different adapter (e.g., 1/2‑20 for coarse imperial, M8 for metric), choose the -01 or -02 options.

• If you require hazardous area approvals (CSA, ATEX), choose the corresponding -03-01 or -03-02/-04 options.

• If you have a custom mounting hole that matches the bare 3/8‑24 body thread, choose the -00-00 to avoid an adapter.

Installation Best Practices for 330500-03-00

1. Surface Preparation – Clean the mounting surface to remove paint, rust, or debris. Achieve a surface finish of 32 µin rms or better. Ensure the threaded hole matches the 1/4‑28 UNF thread and is perpendicular to the measurement axis.

2. Sensor Mounting – Apply a thin layer of anti‑seize compound (if required) and hand‑tighten the sensor (via the adapter) into the hole. Then torque to 32‑46 kg·cm (24‑40 in‑lb). Do not use the connector body to apply torque; use a wrench on the hex flats of the adapter (if provided) or on the 15/16 inch hex flats of the sensor body (if accessible). The 1/4‑28 UNF thread is relatively fine, so careful alignment is important to avoid cross‑threading.

3. Magnetic Base Option – If using the magnetic base (46000‑01), first attach the base to the machine surface, then screw the sensor (with the 1/4‑28 adapter) into the base’s threaded socket. This allows for rapid installation and removal without tools.

4. Cable Connection – Align the 2‑pin connector (Pin A and Pin B) and tighten the coupling nut securely. For long cable runs, use the recommended 18 AWG cable (02173006 or 125065) to minimise voltage drop and signal loss. Route cables away from high‑voltage lines and avoid sharp bends.

5. Grounding – Because the case is isolated, the sensor does not require a separate ground. However, the cable shield should be connected to the monitoring system’s common reference at the power supply end to minimize electrical noise. Do not ground the shield at both ends to avoid ground loops.

6. Environmental Protection – For outdoor installations, use splash boots (available separately) and ensure all cable connections are sealed. The sensor itself is IP68, but the cable termination may require additional protection.

Comparison with Other Fine‑Thread Options – Why Choose 330500-03-00?

• vs. 330500-03-01 (1/4‑28 with CSA) – The -03-01 adds CSA certification for hazardous areas. If your plant is non‑hazardous, the -00 is more economical and does not require certified barriers. Choose -03-00 for safe areas; choose -03-01 for hazardous areas.

• vs. 330500-00-00 (no adapter) – The -00-00 saves cost but requires you to provide your own adapter or mount directly into a 3/8‑24 hole. If you value convenience and have standard 1/4‑28 UNF mounting hardware, the -03-00 is the better choice.

• vs. 330500-01-00 (1/2‑20 UNF) – The -01-00 is for coarse imperial thread. If your mounting hardware uses 1/4‑28 (fine), choose -03-00; if 1/2‑20, choose -01-00. The 1/4‑28 is more common for magnetic bases and compact mounts.

• vs. 330500-02-00 (M8 x 1) – The -02-00 is for metric installations. If your machinery uses imperial fine thread, choose -03-00; if metric, choose -02-00.

Ordering Information

When ordering the 330500-03-00, use the full part number exactly as shown:

• 330500 – Base model (Velomitor Piezo‑velocity Sensor)

• -03 – Mounting Thread Adapter: 1/4‑28 UNF

• -00 – Agency Approval: None

Compatible Cables and Accessories

Note: The 330500-03-00 includes the 1/4‑28 adapter and does not include a cable.

Certifications and Compliance

Because the -00 option has no hazardous area approvals, it is certified for general industrial use only. It complies with:

• 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).

• ABS – (Marine Vessels, Offshore Units) – the sensor itself is approved for maritime use even without explosion protection.

It is NOT rated for ATEX, IECEx, or CSA hazardous locations. If your installation requires intrinsic safety, you must order the -03-01 (CSA) or -03-02 (ATEX) or -03-04 (multiple) options.

Warranty and Support

The Bently Nevada 330500-03-00 is covered under the standard manufacturer’s warranty (refer to Bently Nevada Terms and Conditions). For technical support, application assistance, or custom configurations, contact your local Bently Nevada sales representative or access the Bently Nevada Media Library at bntechsupport.com.