Operation of Bentley Shaft Instrumentation

I. Brief Introduction to Bentley System Composition

• Probe: Typically composed of a coil, head, housing, high-frequency cable, and high-frequency connector, the coil is the core of the probe and the sensitive component of the entire sensor system. The physical dimensions and electrical parameters of the coil determine the linear measurement range of the sensor system and the stability of the probe's electrical parameters. The coil diameter determines the basic performance of the sensor system—its linear range, which is approximately 1/2 to 1/4 of the probe head diameter. Proximity eddy current sensors are available in specifications with head diameters of 5mm, 8mm, 11mm, and 14mm.
• Extension Cable: Available in 5m and 9m specifications, the extension cable length should be selected such that the sum of the extension cable length and the probe cable length matches the length required by the supporting preamplifier (5m or 9m).
• Preamplifier (Oscillator-Demodulator): The preamplifier provides high-frequency alternating current to the probe coil. On the other hand, it senses changes in the probe's parameters caused by the approach of a metal conductor in front of the probe. Through processing by the preamplifier, an output voltage signal is generated that changes linearly with the gap between the probe tip and the measured metal conductor. The maximum length from the preamplifier to the 3500 monitor is 305 meters.
  • The "50" on the preamplifier indicates a total system length of 5m, "0" for panel mounting, "51" for 5m rail mounting, and "52" for 5m installation without hardware. The same logic applies to "90," "91," and "92."

System Cabinet Card Installation View

• Sensitivity for shaft vibration and displacement: 7.874V/mm, with an ideal installation distance of 1.27mm.
• The voltage is 0V when the probe is closest to the metal shaft (lightly touching the measurement surface), and the voltage increases with distance, with a working range of 2mm.
• Probe resistance: 7.3Ω + 0.28Ω/m; extension cable resistance: 0.222Ω/m. Replace the probe if the resistance is extremely low (short circuit), extremely high (open circuit), or shows poor contact.
• Operating temperature ranges:
  • Probe and extension cable: -34~177℃;
  • Preamplifier: -34~66℃;
  • Detector and power supply: -29~66℃.

II. TK3 Tester

• The speed knob on the device adjusts the swash plate speed for vibration testing, while the micrometer measures displacement. The measurement surface should be made of the same material as the actual rotor.
• Note: Copper, aluminum, brass, titanium alloy, etc., are not conventional rotor materials. Take care during calibration to ensure effective monitoring.
• Micrometer: One full rotation (50 grids) equals 0.01mm/grid, totaling 0.5mm per rotation, with a measurement range of 0-25mm. The shaft scale is 1mm/grid.

1. Install the probe with a fixture, gently press it against the fixed micrometer disk surface, and set the micrometer knob to 0.
2. Connect with matching cables and a preamplifier. Connect the negative terminal of the DC power supply to the -24VDC terminal of the preamplifier, and the positive terminal to the COM terminal. Connect a multimeter to the OUT output and COM common terminal.
3. Adjust the micrometer to move 0.25mm away from the probe each time; the multimeter will show a change of approximately 2V. Record upward readings until reaching 3.5mm.
4. For downward adjustments, reduce the distance by 0.25mm each time, record voltage values until reaching 0mm, fill out the calibration form, and evaluate pass/fail.

III. Probe Installation

• Sensitivity: 7.874V/mm; ideal gap: 1.27mm. Thus, the installation zero point is approximately 7.87×1.27≈10V. Each measurement point has two vibration sensor probes installed at 90° to each other (typically horizontal as X and vertical as Y). The X vibration probe is installed on the right side of the vertical centerline, and the Y probe on the left.
• Displacement Installation (Involving Rotor Axial Movement):
  • Method 1: The fitter uses a micrometer to find the midpoint of the axial movement, and the probe is installed to adjust a 10VDC voltage value.
  • Method 2 (higher precision, widely used):
    • The fitter first pries the rotor to the far end to obtain the axial movement value:$V^{\text{far}}=\text{Zero gap voltage (10V)}+\genfrac{}{}{0ex}{}{\text{Axial movement value (e.g., 0.3mm)}}{2}\times \text{Sensitivity (7.87V/mm)}=11.185\text{VDC}$.
    • Pry the rotor to the near end:$V^{\text{near}}=\text{Zero gap voltage (10V)}-\genfrac{}{}{0ex}{}{\text{Axial movement value (0.3mm)}}{2}\times \text{Sensitivity (7.87V/mm)}=8.8195\text{VDC}$.
    • Calculate the accurate midpoint:$\text{Contact Us at Any Time  852--3568 3659  jim@greatsystem.cn  Flat 10, 6/F, Block A, Hi-Tech Ind. Ctr. 5-21 Pak Tin Par St, Tsuen Wan, HK jim@greatsystem.cn Send your inquiry directly to us Submit Now}$