The MX21508 series is an API670-compliant industrial non-contacting eddy current proximity probe developed by US manufacturer Metrix as a drop-in replacement for the Bently Nevada 3300XL 8mm series. Breakdown of model coding:
- 02: unthreaded mounting length of 0.2 inch
- 12: overall probe body length of 12 inches
- 10: total cable length of 1 meter
- 02: miniature male coaxial connector
Items marked WITHOUT BOX are supplied as bare probe with attached cable without original factory paper packaging.
Working on high-frequency eddy current principles, this non-contact probe continuously monitors rotating shaft radial vibration, axial displacement, shaft eccentricity and oil film clearance in real time. A complete sensing system consists of the probe, matching extension cable and either MX2033 preamplifier or MX2034 4-20mA transmitter. It is fully compatible with all Bently Nevada 3300 / 3300XL /7200 monitor racks and serves as the core sensing component for on-line shaft condition monitoring of critical rotating equipment in petrochemical, thermal power and air separation industries, backed by a 36-month original manufacturer warranty.
This 8mm tip variant features a standard measuring range with a linear span of 80mil (2.0mm) and nominal sensitivity of 200mV/mil (7.87mV/μm), making it the mainstream specification for field retrofit of OEM imported proximity probes.
Technical Specifications
1. Mechanical Characteristics
Tip dimension: Standard Φ8mm; tip material is high-temperature resistant insulating PPS (Polyphenylene Sulfide), featuring impact resistance and excellent resistance to oil corrosion.
Mounting type: Reverse Mount design; unthreaded segment length: 0.2 inch, overall probe housing length: 12 inch with standard industry external thread for universal installation.
Cable configuration: 75Ω standard double-shielded coaxial cable with total length of 1 meter (suffix "10" in part number denotes 1m). Double shielding effectively restrains power frequency interference, with outer armored sheath for superior abrasion resistance.
Connector: Miniature male coaxial rear connector, industry-standard RF fitting with secure locking structure to prevent loose connection under vibration.
Weight: Approximately 0.32kg per probe including cable; lightweight construction facilitates installation inside compact bearing housings.
2. Electrical Parameters (Test Condition: 25℃ ambient, 45# steel target, -24VDC power supply)
Nominal sensitivity: 200mV/mil (7.87mV/μm), widely adopted calibration standard compatible with most turbine monitoring systems.
Effective linear range: Start gap 0.25mm, full-scale span 2.0mm (80mil), linearity fully compliant with API670 requirements within the working range.
Frequency response: DC ~ 10kHz (covers rotational speed up to 600,000 RPM), applicable for full operating conditions of high/low-speed steam turbines and reciprocating compressors; signal attenuation ≤5% at 10kHz.
Temperature drift: Span drift ≤3% at 65℃, ensuring stable measurement during long-term operation of high-temperature machinery.
Impedance: System nominal impedance 75Ω coaxial, impedance matched with OEM preamplifiers to eliminate signal reflection and waveform distortion.
3. Environmental Resistance Ratings
Operating temperature: -34℃ ~ +177℃; Storage & transit temperature: -51℃ ~ +177℃.
Ingress protection: IP65 rated against dust and splashing lubricant oil, capable of continuous service immersed in equipment lube oil.
Chemical compatibility: No performance degradation when exposed to lube oil, fresh water, 10% dilute sulfuric acid, ammonia water, MEK ketones and DMF organic solvents.
Application Fields
1. Oil & Gas Industry
On-line monitoring of shaft vibration, axial displacement and thrust clearance for compressors on long-distance oil & gas pipelines, centrifugal compressors for hydrogenation and reforming processes as well as screw compressors in refineries; signal acquisition for shaft protection interlock of equipment installed in hazardous explosive areas.
2. Thermal & Gas Power Generation
Probe matching for TSI safety interlock systems to monitor radial vibration, rotor eccentricity and differential expansion of steam turbine generator sets, gas turbines, boiler induced draft fans and feed water pumps.
3. Air Separation & Coal Chemical Plants
Continuous measurement of shaft displacement and vibration on large centrifugal air compressors, booster compressors and expanders for interlock protection of core rotating machinery in air separation units.
4. Metallurgy & Paper Industry
Non-contact displacement monitoring for large fans, high-speed centrifugal separators and main drive rolls of papermaking machines; early fault warning for high-speed shafts inside gearboxes.
5. General Industrial Pumps
On-line shaft vibration monitoring for high-power centrifugal, screw and gear pumps to pre-alarm bearing bush abrasion and axial shifting failures.
FAQ
Q: Can this probe directly replace original Bently 3300XL 21508 probes? Is on-site configuration modification required?A: Drop-in direct replacement is available. It features full compatibility in sensitivity, impedance and measuring range. No adjustments to preamplifier parameters, rack configuration or mounting bore dimensions are needed; replacement can be completed via plug-and-play during equipment shutdown.
Q: Are extra certification documents required for hazardous area installation?A: The probe is certified with ATEX/IECEx intrinsic safety certificates supplied with English documentation. No additional certification is needed for Zone 1 chemical hazardous locations. Domestic China explosion-proof certification can be applied separately on request.
Q: What components should be prioritized for troubleshooting if continuous signal drift occurs on site?A: Three key inspection points: ① Carbon deposit buildup on probe tip from lube oil; ② Moisture ingress at coaxial connector causing shielding failure; ③ Loose mounting nut resulting in variable probe gap. Issues can be fixed by carbon cleaning, connector drying and nut tightening respectively.
Q: Will the probe degrade rapidly with long-term immersion in high-temperature lubricating oil?A: Original materials pass oil immersion durability tests, delivering a minimum 5-year service life in oil up to 177°C. Custom high-temperature Metrix probes are required for oil temperatures exceeding 180°C.
Q: How to eliminate enlarged measuring error when the target material is not 45# steel?A: Pair with MX2034 smart transmitter. Over 40 preloaded target material curves (stainless steel, cast iron, aluminum, etc.) can be configured inside the transmitter to automatically calibrate sensitivity deviation without replacing the probe.
Q: Is standalone cable replacement possible instead of full probe replacement when outer cable sheath is damaged?A: MX21508 cable and probe tip are integrally molded and non-detachable, requiring full unit replacement for damaged cables. The split-connector MX2030 model allows separate extension cable replacement; this is the key maintenance distinction between the two series.
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