Bently Nevada (Bentley Nevada) 21508-02-12-05-02 – Detailed Explanation of Eddy Current Displacement Probe
I. Basic Information
Brand: Bently Nevada (a subsidiary of Baker Hughes, the leading company in rotating machinery condition monitoring)
Product Series: 7200 Series 8mm Eddy Current Proximity Probe (Proximity Probe)
Origin: United States
Usage: Non-contact measurement of radial vibration of rotating shaft, shaft eccentricity, axial displacement, and rotational speed phase difference. Suitable for monitoring systems of large rotating units such as steam turbines, compressors, fans, pumps, etc.
Model Segmentation (Meaning of Each Segment)
21508 – 02 – 12 – 05 – 02
21508: Basic probe model, representing the 7200 eddy current probe body with an 8mm measurement range
02: Probe thread installation specification (standard installation thread)
12: Probe sensing head structure / thread length parameter
05: Total length of the built-in integrated cable = 0.5m (20 inches)
02: Terminal connector type: Micro coaxial male connector, used for connecting extended cables / preamplifiers
This is a probe with its own short cable. It can be used in combination with the corresponding 7200 series preamplifier (preamplifier) and cannot be directly connected to the 3300XL preamplifier. The 7200 and 3300XL systems are incompatible.
Key Technical Parameters
Effective Measurement Range: 0 – 2mm (8mm probe standard linear range)
Output Characteristics: When combined with the preamplifier, the gap change is converted into a linear voltage output. Typical sensitivity 200mV/μm
Operating Temperature: The probe can withstand high-temperature conditions and is suitable for high-temperature environments inside bearing boxes
Measurement Principle: High-frequency eddy current effect. When the metal of the rotating shaft is close to the probe, the impedance change of the eddy current converts into a displacement signal
Protection: Industrial oil-resistant and oil-stain-resistant cables, suitable for bearing box environments with lubricating oil, water vapor
Compatible Monitoring Framework: Old protection instruments of the 7200 monitoring system of Bently
Practical Application in the Unit
Steam turbines / centrifugal compressors: Radial axial vibration monitoring in the X/Y direction, axial displacement monitoring
Blowers, circulating pumps, motors: Online monitoring of rotor vibration, early warning of bearing wear, rotor imbalance, misalignment
Signal Linkage: Probe → Extended Cable (if needed for lengthening) → Preamplifier → Monitoring Module / PLC/DCS, real-time output of vibration values, triggering interlock shutdown protection when exceeding the limit
Lifecycle and Spare Parts Status
The 7200 series belongs to an outdated discontinued product line. The original factory has mainly promoted the new generation 3300XL / 3500XL series probes;
The market circulation mainly consists of brand-new inventory, good pre-assembly second-hand parts, and third-party refurbished and calibrated parts;
A large number of old power plants / refining and petrochemical old units are still in service, and the demand for spare parts is relatively strong.
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