Bently Nevada 21508-02-12-10-02 Eddy Current Proximity Probe Product Specification

21508-02-12-10-02 is a factory pre-calibrated reverse mount 5 mm eddy current proximity probe designed for Bently Nevada 7200 series transducer system. Paired with 2155/00 proximitor and matching calibrated 75-ohm extension cable, it constitutes a complete non-contact measuring system complying with API 670 machinery protection standards. Working on eddy-current induction principle, the probe converts gap variations between sensing tip and metallic rotating target into linear analog voltage signals, which are transmitted to 7200 or 3500 rack modules for real-time monitoring of rotor radial vibration, axial thrust displacement and Keyphasor pickup on steam turbines, gas turbines, centrifugal compressors and large turbo-generators across power, petrochemical and metallurgical industries. Every finished unit undergoes linearity calibration, cyclic temperature aging and hermetic sealing inspection before shipment to maintain stable accuracy under harsh environments with high temperature, lubricant oil mist and heavy electromagnetic interference from variable frequency drives and high-current power lines.

Each coded segment follows Bently’s standard naming specification for 7200-series reverse installation probes. Base code 21508 represents the core 5 mm reverse-mounted proximity probe platform exclusively for the 7200 transducer lineup. Segment 02 defines internal coil structure, electrical layout and factory preset calibration parameters for the sensing assembly. Segment 12 specifies the standard threaded body dimension for rear-side reverse mounting. Segment 10 stands for fixed factory-molded integral cable length of 1.0 meter permanently attached to probe body. Final segment 02 indicates miniature coaxial connector fitted at cable end for interconnection with matched extension cable. Units with different digit combinations carry distinct mechanical dimensions and calibrated electrical values and cannot be swapped randomly on-site; improper substitution invalidates full-loop factory calibration and causes measurement deviation or accidental protection trip.

Probe housing and sensing tip are fabricated from high-strength corrosion-resistant stainless steel to resist oil erosion and corrosive vapor inside confined bearing housings. The internal induction coil is fully potted with high-temperature epoxy resin to eliminate internal air gaps, preventing coil shifting or inter-turn short-circuit induced by long-term equipment vibration and ambient temperature swings. The attached 1-meter integral cable features controlled 75-ohm impedance construction with dense tinned copper braided shielding over 95% coverage to suppress external electromagnetic crosstalk during signal transmission. Field cutting, splicing or connector replacement on the original integral cable is strictly forbidden, as any physical modification permanently voids original factory calibration. Reverse mounting structure allows installation from the back of bearing pedestals, ideal for compact equipment spaces lacking front-side mounting access. Built-in fault detection capability identifies open or short circuit via obvious output voltage drift to simplify on-site troubleshooting. Stable linear output is only retained when assembled with original certified extension cable and designated 2155-series proximitor.

The matched proximitor supplies regulated negative DC power ranging from -17.5 VDC to -26 VDC, with typical field operating voltage at -24 VDC. Factory fixed calibrated sensitivity is 7.87 V/mm (200 mV/mil) referenced to standard AISI4140 carbon steel target, with full-range linearity tolerance controlled within ±5% per API 670 requirement. Valid linear measuring range covers 0 mm to 1.27 mm for small-gap radial vibration and short-stroke axial displacement measurement. Frequency response spans DC up to 10 kHz to capture both slow static thermal expansion drift and high-frequency dynamic shaft vibration signals. Recommended pre-installation gap is set near the midpoint of linear range to secure stable operating bias voltage for long-term continuous operation.

Permissible continuous operating temperature for the probe sensing section ranges from -35°C to +120°C to accommodate high-temperature surroundings close to hot bearing housings and turbine casings. Spare storage temperature is kept between -55°C and +85°C within dry non-condensing storage space; applicable relative humidity is 5%RH~95%RH without dew condensation on cable and housing surfaces. The probe withstands routine mechanical vibration of 10 Hz ~ 2 kHz from adjacent running rotating machinery. Long-term immersion in corrosive liquid, acid mist and sustained high-temperature steam is prohibited to avoid insulation degradation and outer casing damage. For installation above 1000 meters altitude, shorten periodic inspection interval appropriately.

Cut off power of the whole monitoring channel prior to installation, mount the probe from the rear threaded hole of bearing pedestal or custom fixture, adjust pre-set gap to design value and lock fastening nut against operational loosening. Route probe cable separately away from high-current AC cables and inverter wiring to minimize electromagnetic coupling interference. Avoid sharp small-radius bending, overstretching and heavy squeezing on cable body to prevent internal core damage and impedance shift. During regular maintenance cycles, inspect cable outer jacket for oil corrosion, abrasion and cracking, and check connector locking tightness. When replacement is required after failure, only spare with identical full part number 21508-02-12-10-02 is permitted for direct swap. All replacement probes complete impedance testing and calibration matching before factory delivery to guarantee full interchangeability within original measurement loops.