Bently Nevada 21508-02-12-05-02 Eddy Current Proximity Probe Product Specification
21508-02-12-05-02 is a factory pre-calibrated reverse-mounted 5 mm eddy current proximity probe developed for Bently Nevada 7200 series transducer system. When combined with matching 2155/00 proximitor and certified 75-ohm extension cable, it forms a complete non-contact measurement system complying with API 670 industrial machinery protection specifications. Based on eddy current induction principle, the probe converts clearance variation between its sensing tip and conductive metallic rotating target into proportional linear analog voltage signals. These signals are transmitted to 7200 or 3500 rack-mounted monitor modules to achieve continuous online measurement of rotor radial vibration, short-stroke axial displacement and Keyphasor rotational pulse signals for critical rotating equipment. Widely used on steam turbines, gas turbines, centrifugal compressors and large turbo-generators in power generation, petrochemical and metallurgical industries, the probe supports preset alarm and emergency shutdown interlock functions to guarantee unit operational safety. Every finished probe undergoes linearity calibration, high-low temperature cycling aging and hermetic sealing inspection before factory delivery to maintain stable measuring accuracy under severe on-site conditions including high ambient temperature inside bearing housings, pervasive lubricating oil mist and complex electromagnetic interference from high-power motors and variable frequency drives.
Description
Bently Nevada 21508-02-12-05-02 Eddy Current Proximity Probe Product Specification
1. Product Overview
21508-02-12-05-02 is a factory pre-calibrated reverse-mounted 5 mm eddy current proximity probe developed for Bently Nevada 7200 series transducer system. When combined with matching 2155/00 proximitor and certified 75-ohm extension cable, it forms a complete non-contact measurement system complying with API 670 industrial machinery protection specifications. Based on eddy current induction principle, the probe converts clearance variation between its sensing tip and conductive metallic rotating target into proportional linear analog voltage signals. These signals are transmitted to 7200 or 3500 rack-mounted monitor modules to achieve continuous online measurement of rotor radial vibration, short-stroke axial displacement and Keyphasor rotational pulse signals for critical rotating equipment. Widely used on steam turbines, gas turbines, centrifugal compressors and large turbo-generators in power generation, petrochemical and metallurgical industries, the probe supports preset alarm and emergency shutdown interlock functions to guarantee unit operational safety. Every finished probe undergoes linearity calibration, high-low temperature cycling aging and hermetic sealing inspection before factory delivery to maintain stable measuring accuracy under severe on-site conditions including high ambient temperature inside bearing housings, pervasive lubricating oil mist and complex electromagnetic interference from high-power motors and variable frequency drives.
2. Part Number Definition Breakdown
Each segment of 21508-02-12-05-02 follows Bently’s standard part coding rules for 7200-series reverse installation proximity probes. Base code 21508 represents the core product series for 5 mm reverse-mounted proximity probes dedicated to the 7200 transducer platform. The second segment 02 defines fixed internal coil layout, internal wiring structure and factory locked electrical calibration parameters for reverse mounting configuration. The third segment 12 specifies standardized threaded body dimension designed for rear-side installation into bearing pedestal mounting holes or custom fixtures. The fourth segment 05 stands for factory pre-molded integral cable fixed length of 0.5 meter permanently attached to the probe main body. The final segment 02 indicates miniature coaxial connector mounted at cable terminal for plug-in connection with original matched extension cable. Any probe with differing segment codes features varied mechanical dimensions or calibrated electrical parameters and cannot be directly replaced on-site; improper substitution will invalidate full-loop factory calibration and result in measurement drift or undesired equipment protection trip.
3. Core Functional Characteristics
The probe threaded housing and sensing head are manufactured from high-strength corrosion-resistant stainless steel, delivering reliable resistance against lubricant erosion and weak corrosive vapor within confined bearing compartment environments. Internal induction coil is fully encapsulated with high-temperature epoxy potting material to eliminate internal air gaps, effectively preventing coil displacement or inter-turn short-circuit triggered by long-term equipment vibration and ambient temperature fluctuation. The attached 0.5-meter integral cable adopts 75-ohm controlled-impedance coaxial structure with high-density tinned copper braided shielding exceeding 95% coverage to restrain external electromagnetic noise during signal transmission. Field cutting, splicing or replacement of original integral cable and end connector is strictly forbidden, as any physical modification permanently cancels factory preset calibration data. Reverse mounting design enables installation from the back of equipment mounting base, which is suitable for narrow installation space unavailable for front threading operation. Built-in open/short-circuit fault diagnosis function identifies abnormal wiring state via obvious output voltage offset to facilitate convenient on-site troubleshooting. Consistent linear performance of the whole measurement system can only be maintained by full matching with original certified extension cable and designated 2155-series proximitor preamplifier.
4. Electrical and Metrological Specifications
The matched proximitor provides regulated negative DC power ranging from -17.5 VDC to -26 VDC, and -24 VDC is the standard operating voltage used in field application. Factory fixed sensitivity is 7.87 V/mm (200 mV/mil) calibrated with standard AISI4140 carbon steel target, with full-range linearity error controlled within ±5% per API 670 standard. Valid linear measuring range covers 0 mm to 1.27 mm for conventional small-gap radial vibration and short-travel axial displacement measurement. Effective frequency response ranges from DC up to 10 kHz to collect both low-frequency static thermal expansion drift signals and high-frequency dynamic shaft vibration signals simultaneously. Recommended pre-installation clearance is set near the midpoint of linear range to secure a stable operating bias point during long-term continuous equipment running.
5. Environmental Working Parameters
Continuous permissible operating temperature of probe sensing part is from -35°C to +120°C to adapt high-temperature installation close to hot bearing housings and turbine casings. Spare storage temperature is maintained between -55°C and +85°C under dry non-condensing storage surroundings; applicable working relative humidity ranges 5%RH to 95%RH without dew condensation accumulating on probe housing and cable outer jacket. The probe can withstand routine industrial vibration of 10 Hz ~ 2 kHz generated by adjacent running rotating machinery. Long-term continuous soaking in corrosive liquid, acid mist and persistent high-temperature steam is prohibited to avoid outer casing corrosion and inner insulation aging damage. For installation locations above 1000 meters altitude, shorten regular inspection cycle appropriately.
6. Installation and Routine Maintenance Guidance
Cut off power supply of the whole monitoring loop before field installation, mount the probe reversely from rear reserved threaded hole of bearing pedestal or custom mounting bracket, adjust pre-set installation gap to design value and lock fastening nut to prevent loosening caused by long-period operational vibration. During wiring layout, separate probe signal cable away from high-current AC power cables and inverter output lines to reduce cross electromagnetic coupling interference. Within regular maintenance cycles, periodically inspect cable outer sheath for oil corrosion, abrasion and cracking, and check locking tightness of terminal connector. When probe failure requires replacement, only spare part with identical full part number 21508-02-12-05-02 is allowed for direct swap. All replacement probes complete full electrical performance testing and alternating temperature aging screening before factory delivery to ensure complete interchangeability inside original vibration monitoring loops.
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