21508-02-12-10-02 | Bently Nevada Vibration Probe

Bently Nevada 21508-02-12-10-02 Reverse-Mount Proximity Probe System

Product Introduction

The Bently Nevada 21508-02-12-10-02 belongs to the 7200 Proximity Transducer Systems family. This system delivers non-contact vibration and position measurements for rotating machinery. The reverse-mount probe configuration distinguishes this model from standard designs. Specifically, the probe threads onto the housing from the inside, which saves external space. This design proves invaluable for installations with limited clearance around the machine casing. Additionally, the system includes a 1.0-meter cable with a miniature male coaxial connector.

Technical Specifications

The 21508 series offers specialized configurations for challenging mounting scenarios. The base model number 21508-02-12 indicates a reverse-mount probe with specific thread and diameter characteristics. Total length option 10 specifies a 1.0 metre (39 inches) cable. The tolerance allows +0.25 metre and -0.10 metre (+10 inches, -4 inches) for flexible installation. Connector option 02 adds a miniature male coaxial connector for straightforward system integration.

The tip construction features an 8 mm diameter with reverse-mount case configuration. Thread type 3/8-24 ensures compatibility with standard mounting provisions. This model includes no lead armor, which distinguishes it from armored versions. For power input, the system accepts -17.5 Vdc to -26 Vdc at 12 mA maximum consumption. This wide input range simplifies integration with existing power sources.

Output Performance

The 21508-02-12-10-02 provides a calibrated range of 80 mils (2.0 mm) . Measurement begins at approximately 10 mils (0.25 mm) from the probe face. Consequently, the system offers consistent readings across a useful gap range. Scale factor measures 200 mV/mil (7.87 V/mm) with ±4% accuracy when calibrated as a system. Including interchangeability errors, accuracy remains within ±9.5%. Linearity stays within 0.8 mils (0.02 mm) of a 200 mV/mil straight line for system calibration. With interchangeability errors included, linearity reaches within 2.3 mils (0.06 mm).

Frequency response covers 0 to 10 kHz (0 to 600,000 cpm) . At 10 kHz, the response drops by only -5%, which preserves signal quality at high rotational speeds. Temperature sensitivity typically shows a -3% change in scale factor at +150°F (+65°C) at 50 mils gap (1.27 mm). This predictable characteristic enables effective temperature compensation during operation.

Environmental and Mechanical Limits

The Bently Nevada 21508 system operates reliably across extreme conditions. The Proximitor functions from -60°F to +212°F (-51°C to +100°C). Meanwhile, the probe and extension cable perform from -30°F to +350°F (-34°C to +177°C). This broad range accommodates both cold startups and high-temperature processes. Relative humidity tolerance reaches 95% non-condensing, which prevents moisture-related measurement errors.

Corrosion resistance applies specifically to 8 mm probes such as this model. Direct contact with air, water, lube oil, ammonium hydroxide, and sulfuric acid (10%) does not impair probe operation. Additionally, MEK (methyl-ethyl ketone) or DMF (Dimethylformamide) also cause no performance degradation. This chemical resilience enhances suitability for petrochemical and refinery environments. The complete system weighs approximately 1.3 lbs (0.59 kg). With packaging, the gross weight reaches about 0.70 kg.

Installation Guidance for Reverse-Mount Probes

Installing the 21508-02-12-10-02 requires understanding the reverse-mount concept. First, access the inside of the housing or bearing casing where the probe will mount. Thread the probe through the 3/8-24 hole from the inside outward. This reverse orientation positions the probe tip facing the target surface. Therefore, the cable routes internally rather than externally.

Proper gap setting remains critical for measurement accuracy. The calibrated range begins at 10 mils from the probe face. Set the initial gap within this range for optimal signal output. For best results, use a calibration fixture to verify the scale factor before final installation. Also, confirm the power supply delivers the correct -17.5 Vdc to -26 Vdc input. The 1.0-metre cable provides sufficient reach for most internal routing configurations.

Packaging and Delivery

Your purchase ships as a new, original unit in factory packaging. The package contains the following items:

• 1 x 21508 Proximity Transducer System (complete assembly)

• 1 x 8 mm reverse-mount probe with attached 1.0m cable and coaxial connector

• 1 x Installation and setup documentation

We ship the product new and guarantee its authenticity. The packaging prevents damage during transit. We ship worldwide using trusted couriers. Our standard shipping partners include FedEx, UPS, and DHL.

Frequently Asked Questions (FAQ)

1. What makes the reverse-mount design different from standard probes?
The 21508-02-12-10-02 threads into the housing from the inside. This configuration saves external space and suits installations with limited clearance around the machine casing.

2. What probe diameter and thread size does this model use?
This model features an 8 mm diameter probe with 3/8-24 threads. The reverse-mount case configuration accommodates specific housing designs.

3. Does this probe include lead armor for cable protection?
No. This model includes no lead armor. This differs from some other 21508 configurations that offer armored cable options.

4. What is the calibrated range and scale factor for this system?
The system provides an 80 mil (2.0 mm) calibrated range with a 200 mV/mil scale factor. Accuracy reaches ±4% when calibrated as a complete system.

5. What temperature range can this probe withstand?
The probe and extension cable operate from -30°F to +350°F (-34°C to +177°C). The Proximitor operates from -60°F to +212°F (-51°C to +100°C).