The Bently Nevada 330500-02-00 Velomitor is a high-performance piezo-velocity sensor designed to measure absolute casing vibration on rotating machinery. Unlike traditional moving-coil velocity transducers that suffer from mechanical wear and orientation limitations, the 330500 utilizes solid-state piezoelectric technology. This advanced sensor integrates an accelerometer and an electronic integrator into a single rugged package, providing a velocity output directly proportional to the vibration of the machine housing.
It plays a vital role in protecting critical assets such as steam turbines, centrifugal pumps, and fans. By capturing high-frequency vibration data with microscopic precision, it allows maintenance teams to identify structural resonances, loose components, or bearing housing instabilities. Its omnidirectional mounting capability and hermetically sealed stainless steel housing ensure it remains the industry standard for reliability in Turbine Supervisory Instrumentation (TSI) and balance-of-plant applications.
The model 330500-02-00 follows a specific configuration that determines its mounting interface and hazardous area certification:
The -02 designation indicates a 1/4-28 UNF mounting thread. This is the most common mounting interface for North American industrial standards, ensuring a rigid mechanical connection between the sensor and the bearing housing for accurate high-frequency signal transmission.
The -00 suffix specifies No Agency Approvals (Standard). This version is intended for general-purpose industrial environments that do not require specialized explosion-proof or intrinsically safe certifications like ATEX or CSA. It offers the same precision and durability as certified models but at a more economical price point for non-hazardous locations.
| Feature | Specification Details |
| Sensitivity | 3.94 mV/mm/s (100 mV/in/s) ±5% |
| Frequency Response | 4.5 Hz to 5.0 kHz (±3.0 dB) |
| Velocity Range | 1270 mm/s (50 in/s) peak |
| Transverse Sensitivity | Less than 5% of sensitivity |
| Operating Temperature | -55 °C to +121 °C (-67 °F to +250 °F) |
| Housing Material | 316L Stainless Steel (Hermetically Sealed) |
| Connector Type | 2-pin Mil-C-5015 |
| Excitation Voltage | -24 VDC (Nominal) |
Achieving accurate velocity measurements depends heavily on the mechanical integrity of the sensor installation:
The sensor must contact a flat, smooth surface (at least 25mm in diameter) to ensure linear response at high frequencies. Always apply a thin film of silicone grease or acoustic couplant to the mounting surface before torquing the sensor to fill microscopic air gaps that can attenuate high-frequency signals.
Tighten the 330500-02-00 to a torque of 4.5 N·m (40 in·lb). Unlike older moving-coil sensors, the Velomitor is omnidirectional; you can install it vertically, horizontally, or at any intermediate angle without re-calibrating or losing measurement accuracy.
Use a shielded, twisted-pair cable for signal transmission. The sensor housing is isolated from the internal electronics to prevent ground loops. Ensure the cable shield is grounded only at the monitoring rack (e.g., Bently Nevada 3500) and never at the sensor end to avoid electrical noise interference from large motors or VFDs.
Solid-State Reliability: By eliminating internal moving parts, the Velomitor prevents the "stiction" and mechanical fatigue issues that plague traditional velocity pickups, significantly extending service life.
Direct Velocity Output: The internal integration circuit converts acceleration to velocity within the sensor, providing a low-impedance signal that is highly resistant to cable noise and suitable for long-distance transmission.
Broad Frequency Range: The 4.5 Hz to 5 kHz range allows the sensor to detect both low-speed structural issues and higher-frequency gear mesh or blade pass frequencies.
Rugged Environment Protection: The hermetically sealed 316L stainless steel case protects the internal piezo-elements from moisture, oil, and corrosive industrial atmospheres.
Q1: How do I verify if the 330500-02-00 is receiving power?
A1: The Velomitor operates on a constant current source from the monitoring rack. You can verify the "Bias Out" voltage using a multimeter between the signal and common leads. A healthy sensor typically shows a bias voltage between -10 VDC and -14 VDC.
Q2: Can I use this sensor with a standard Ethernet router?
A2: No. This is a common misconception in some inventory listings. The 330500 is an analog sensor that requires a specific -24VDC power source and an interface module (like a 3500/42M monitor). It does not have an RJ45 port or digital networking capabilities.
Q3: What happens if I over-torque the sensor during installation?
A3: Over-torquing can damage the base of the stainless steel housing or strip the 1/4-28 UNF threads. More importantly, it can induce internal stress on the piezoelectric crystal, causing a shift in sensitivity or "DC bias drift." Always use a calibrated torque wrench.
Q4: Is the 330500-02-00 suitable for high-temperature turbine casings?
A4: This model is rated up to 121°C (250°F). For steam turbine applications where casing temperatures exceed this limit, you must use a heat-insulating spacer or opt for the high-temperature version (Bently Nevada 330750).
