Bently Nevada 330500-04-01 Velomitor Piezo-velocity Sensor

The Bently Nevada 330500-04-01 is a specialized configuration of the industry‑standard 330500 Velomitor Piezo‑velocity Sensor, engineered for critical machinery monitoring in North American hazardous (classified) locations where a coarse‑thread universal mounting standard is preferred, featuring a factory‑installed 1/4‑20 UNC thread adapter for compatibility with a wide range of general‑purpose mounting hardware, combined with CSA certification for intrinsic safety. This variant carries CSA approval (suffix -01) and is equipped with a 1/4‑20 UNC mounting adapter (suffix -04), making it the ideal choice for installations in the United States and Canada that require compliance with CSA standards for Class I, Division 1, Groups A, B, C, D; Class II, Groups E, F, G; and Class III hazardous areas, while also benefiting from the coarse thread that offers fast installation, universal availability, and excellent tolerance for field conditions.

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 330500-04-01 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 -04-01 variant is supplied with a 1/4‑20 UNC adapter already threaded onto the body, ready for immediate installation using standard 1/4‑20 mounting hardware, and carries CSA certification for use in explosive atmospheres.

This introduction focuses exclusively on the 330500-04-01 configuration, highlighting its unique combination of CSA certification and coarse‑thread convenience, comparing it with other adapter options (e.g., -00-01 with no adapter, -01-01 with 1/2‑20 UNF, -03-01 with 1/4‑28 UNF) and with other certification options (e.g., -04-00 without approvals, -04-02 with ATEX) to guide proper selection for North American hazardous‑area applications where coarse‑thread mounting is preferred and safety compliance is paramount.

Functional Description and the Advantage of CSA Certification with 1/4‑20 UNC Coarse‑Thread Mounting

The 330500-04-01 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 330500-04-01 is designed to be mounted directly on the machine casing or bearing housing using the supplied adapter. The 1/4‑20 UNC thread is a coarse‑pitch thread (20 threads per inch) that is one of the most widely used and universally available thread standards in the United States and many other regions. It is commonly found on a vast array of mounting hardware, including studs, bolts, and threaded holes in machinery casings. The coarse pitch offers several practical advantages in hazardous area installations: it is less susceptible to cross‑threading when working in confined spaces or with gloves, allows for faster installation and removal (critical for maintenance in hazardous zones), provides greater tolerance for dirt, corrosion, and debris on threads, and offers excellent holding power for the sensor under vibration. Unlike fine threads, which require precise alignment and careful torque control, the 1/4‑20 UNC thread is forgiving and user‑friendly, making it a preferred choice for field installations where speed and reliability are essential.

The -01 certification adds CSA approval for use in hazardous locations under the Canadian and U.S. standards. The sensor carries the following CSA markings (as per the datasheet):

• Class I, Division 1, Groups A, B, C, D (gas/vapor atmospheres)

• Class II, Groups E, F, G (combustible dusts)

• Class III (fibers/flyings)

• Temperature class T3, with ambient temperature range -55°C ≤ Tamb ≤ +121°C.

Additionally, the sensor meets the entity parameters for intrinsic safety: Ui = 28 V, Ii = 100 mA, Pi = 0.84 W, Ci = 10.8 nF, Li = 0 μH. These parameters are critical for selecting an appropriate intrinsic safety barrier and for ensuring compliance with the Canadian Electrical Code and National Electrical Code (NFPA 70).

The combination of the 1/4‑20 adapter and CSA certification makes the 330500-04-01 a versatile and safe transducer for North American hazardous areas where coarse‑thread mounting is desired. It eliminates the need for a separate adapter purchase, saving time and reducing potential installation errors. The adapter is factory‑installed and properly torqued, ensuring a reliable mechanical connection. This configuration is particularly valuable for maintenance teams working in hazardous areas who need to install or remove sensors quickly and reliably, as the coarse thread allows for rapid engagement and disengagement even with gloved hands or in low‑visibility conditions.

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 330500-04-01 with other common configurations: the 330500-04-00 (1/4‑20 UNC adapter, no approvals), the 330500-00-01 (no adapter, CSA), the 330500-01-01 (1/2‑20 UNF adapter, CSA), the 330500-03-01 (1/4‑28 UNF adapter, CSA), and the 330500-04-02 (1/4‑20 UNC adapter, ATEX). This comparison highlights the unique value of the -04-01 for coarse‑thread, CSA‑certified applications.

Selection Guide – Key Differences

The 330500-04-01 is the only coarse‑threaded, CSA‑certified configuration in the 330500 series. Choose this variant when:

• You need CSA certification for hazardous locations in North America.

• You prefer the 1/4‑20 UNC coarse thread for its universal availability, ease of installation, and tolerance for field conditions.

• You want a factory‑installed, properly torqued adapter for reliable mechanical connection.

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

If you need a different adapter (e.g., 1/2‑20 for heavier mounts, 1/4‑28 for fine thread) with CSA, choose -01-01 or -03-01. If you require ATEX instead of CSA, choose -04-02. For global deployments requiring both, choose -04-04 (CSA+ATEX).

Hardware Characteristics – Specific to 330500-04-01

Physical Dimensions and Mounting

• Adapter Thread: 1/4‑20 UNC (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).

• 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 330500-04-01 is compatible with the same two‑conductor shielded cables as all 330500 variants. For hazardous area installations, the cable must be suitable for intrinsic safety and must meet the entity parameter limits per CSA requirements. 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). In hazardous areas, cable capacitance and inductance must be added to the sensor's Ci and Li, and the total must not exceed the barrier's limits.

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)

CSA Hazardous Area Compliance – Detailed for 330500-04-01

The 330500-04-01 is certified to the following CSA standards (as per the datasheet):

• Class I, Division 1, Groups A, B, C, D – For flammable gases or vapors in normal operating conditions.

• Class II, Groups E, F, G – For combustible dusts.

• Class III – For ignitable fibers or flyings.

• Temperature class T3 (maximum surface temperature 200°C under fault conditions), with ambient temperature range -55°C ≤ Tamb ≤ +121°C.

Entity Parameters (for intrinsic safety):

Conditions of Safe Use (per CSA):

• The sensor must be connected to an associated intrinsically safe apparatus that meets the entity parameters.

• The interconnecting cable must have capacitance and inductance such that the total (sensor + cable) does not exceed the barrier’s limits.

• Installation must comply with the Canadian Electrical Code (C22.1) and/or National Electrical Code (NFPA 70).

Installation Best Practices for 330500-04-01 in CSA‑Certified Installations

1. Intrinsic Safety Barrier – Always connect the sensor through a CSA‑certified intrinsic safety barrier that limits voltage, current, and power to within the entity parameters. Ensure the barrier’s output parameters (Uo, Io, Po) do not exceed Ui, Ii, and Pi.

2. Cable Selection and Length Calculation – The sensor’s Ci (10.8 nF) and Li (0 μH) must be added to the cable’s capacitance and inductance. The total must not exceed the barrier’s allowable cable parameters. For long runs, use lower‑capacitance cables (e.g., 18 AWG) to maximize allowable length. Consult the barrier manufacturer’s documentation for cable length calculations.

3. Mounting 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 1/4‑20 UNC thread and is perpendicular to the measurement axis. Apply anti‑seize compound if required, and torque the adapter (or sensor body) 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 or the 15/16 inch hex flats of the sensor body.

4. Cable Connection – Align the 2‑pin connector (Pin A and Pin B) and tighten the coupling nut securely. In hazardous areas, ensure the connector is properly mated and sealed (IP54 or better) to prevent ingress.

5. Grounding – The case is isolated, so grounding is not required for the sensor body. However, the cable shield should be grounded at the power supply end (typically at the barrier) to minimize noise. Do not ground the shield at both ends to avoid ground loops.

6. Environmental Protection – Although the sensor is IP68, the cable termination and connectors require additional protection (splash boots, conduit, etc.) for outdoor or wet locations.

Comparison with Other CSA‑Certified Options – Why Choose 330500-04-01?

• vs. 330500-04-00 (1/4‑20, no approvals) – The -04-00 is for safe areas only. If your installation is in a hazardous area, the -04-01 is mandatory for CSA compliance. The -04-01 provides the same coarse‑thread convenience but adds critical safety certification.

• vs. 330500-00-01 (no adapter, CSA) – The -00-01 offers the same CSA certification but without a pre‑installed adapter. If you have a custom mounting hole that matches the 3/8‑24 body thread or you want to use a different adapter, the -00-01 is more flexible. However, if you want a ready‑to‑mount 1/4‑20 adapter, the -04-01 saves time and ensures proper torque.

• vs. 330500-01-01 (1/2‑20 adapter, CSA) – The -01-01 is for larger fine‑thread mounts. If your mounting hardware uses 1/4‑20 (coarse, smaller), choose -04-01. If 1/2‑20, choose -01-01. The 1/4‑20 is more common for general‑purpose hazardous area installations.

• vs. 330500-03-01 (1/4‑28 adapter, CSA) – Both are 1/4‑inch diameter, but the -03-01 is fine thread (28 TPI) while the -04-01 is coarse thread (20 TPI). Choose -04-01 for faster installation, better tolerance for dirt/debris, and easier handling in hazardous areas; choose -03-01 for precision applications requiring fine adjustment.

• vs. 330500-04-02 (1/4‑20, ATEX) – The -04-02 is for European hazardous areas (ATEX). If your installation is in North America and requires CSA, choose -04-01. If you need both, choose -04-04.

Ordering Information

When ordering the 330500-04-01, use the full part number exactly as shown:

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

• -04 – Mounting Thread Adapter: 1/4‑20 UNC

• -01 – Agency Approval: CSA (US/Canada)

Compatible Cables and Accessories for Hazardous Areas

Note: The 330500-04-01 includes the 1/4‑20 adapter and does not include a cable. Ensure cables and barriers are CSA‑certified for hazardous area use.

Certifications and Compliance – Special Note

The 330500-04-01 carries CSA certification for North American hazardous locations. It also complies with FCC Part 15, EMC Directive 2014/30/EU, RoHS Directive 2011/65/EU, China RoHS (EFUP 15 years), and ABS Marine. It is NOT certified to ATEX or IECEx; for those, select -04-02 or -04-04 options.

Warranty and Support

The Bently Nevada 330500-04-01 is covered under the standard manufacturer’s warranty. For technical support, application assistance, or help with CSA certification documentation, contact your local Bently Nevada representative or access the Bently Nevada Media Library at bntechsupport.com.