【2026 Axis Instruments】Selection Method for Bentley Eddy Current Probe Extensions
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The Bentley eddy current probe (3300 XL) must be used with an original series extension cable； The total length of the probe cable + extension cord must = 5m or 9m ； Impedance 75Ω, capacitive matching ； Environmental temperature, armor, and shielding are selected as needed.
I. Total system length (critical) The 3300 XL 8mm system allows only two total lengths (probe’s built-in cable + extension cable): 5m system: commonly used. 9m system: Long distance. Example (330103 probe, length code = meters × 10): Probe of 1m length (330103-00-10-…) → combined with a 4m extension cable → total length of 5m. Probe 1m → with 8m extension cable → total length 9m. Probe 5m → Attach 0m (no extension needed) → Total length 5m.
II. How to choose the extension cable model (3300 XL is commonly used) 1) 330130 series (standard type, most commonly used) Model: 330130-XX-00-05 XX = length (e.g., 040 = 4m, 045 = 4.5m, 080 = 8m). Features: 75Ω, FEP insulation, standard jacket, -52°C~+121°C.
2) 330180 series (high temperature/armored) Model: 330180-XX-RU (RU=universal) High temperature: PFA insulation, -51°C~+177°C. Armor: Stainless steel weaving, resistant to impact and rodent bites.
III. Electrical matching principles (do not substitute arbitrarily) Impedance: Must be 75Ω (system calibration value). Capacitance: Strictly matched to the preamplifier oscillation circuit by the original manufacturer ； Ordinary cables can cause sensitivity drift and false alarm activations. Connector: Must be ClickLoc/CableLoc gold-plated. Connector, hand-tightened +1/4 turn, IP67.
IV. Environment and Installation Selection Temperature: ≤121℃, select 330130； >At 121℃, choose 330180 (PFA). Interference: For high EMI (motors/inverters), use double shielding (330180). Mechanical protection: Stainless steel armor is used for gutters/trample areas. Laying: Keep away from power cables (≥30cm) ； 90° intersection ； Intermediate connectors are prohibited.
V. Common mistakes ❌ Using ordinary coaxial/cable as a substitute: impedance/capacitance mismatch, resulting in measurement drift. ❌ The total length is not 5/9 m: The preamplifier cannot be calibrated, resulting in incorrect sensitivity. ❌ Mixing different brands: incompatible connectors/shielding, causing significant interference. ❌ Indirect junction boxes: increase contact resistance and introduce noise.
VI. Selection Steps 1. Check the probe model → Confirm the length of the cable included (e.g., 330103-00-10-…=1m). 2. Determine the total system length: 5m or 9m. 3. Calculate the extended length: total length − probe length. 4. Select series: Standard → 330130 ； High temperature/armored → 330180. 5. Model designation: 330130-XX-00-05 (XX = extension length × 10).
The following response is for reference: A complete 3300 XL 8mm eddy current sensor system must consist of 3 core components: The probe – the \"scout\" that is screwed onto the machine housing and faces the rotating shaft, and it is responsible for directly capturing signals related to changes in the gap. Extension cable: The “signal highway” that connects the probe and the preamplifier; its length is strictly specified, and it must not be connected arbitrarily. Preamplifier: A \"signal processor\" installed in the cabinet that converts the high-frequency, low-level signals from the probe into direct current voltage signals that can be understood by us and recognized by the cards.
In essence, the principle is quite simple: when high-frequency electricity is applied to the probe, an alternating electromagnetic field is generated； When the metal shaft under test comes close to the probe, eddy currents are induced on its surface, which in turn alters the intensity of the electromagnetic field ； The preamplifier accurately converts this change in magnetic field into a linear DC voltage signal; the closer the shaft is to the probe, the more negative the output voltage becomes ； The farther away, the less negative the voltage.
Let’s correct a very common misconception: the so-called “Bentley 8mm sensor” is by no means a single probe; it is rather a complete measurement system, and none of its components can function without the others.