Measurement principles, fault diagnosis, and circuit testing of shafting instruments
Thread Content
This post was last edited by HaiChuan LaoYu on 2026-5-5 08:11. I. Principle of measurement using shaft instrumentation (TSI/electromagnetic induction sensor systems) 1. System components Probe: A coil that generates a high-frequency magnetic field. Extension cable: Connects the probe to the proximitor. Proximitor: Generates high-frequency oscillations, processes signals, and outputs a voltage corresponding to the gap. Monitoring card/frame (such as 3500, 3300): Provides display functions, alarms, interlocks, and a 4–20mA output. 2. Basic principle of electromagnetic induction (applicable to shaft vibration/axial displacement/eccentricity/keyway alignment/speed measurement) The proximitor generates a high-frequency alternating current of around 1MHz, which is sent to the probe coil to create a high-frequency magnetic field. A magnetic field near the surface of the metal shaft → induces eddy currents inside the metal. The eddy currents generate a reverse magnetic field that counteracts the probe’s magnetic field, causing the coil impedance/voltage to vary with the gap. The smaller the gap → the stronger the eddy currents → the lower the coil voltage ； The larger the gap, the higher the voltage. The preamplifier converts the gap variation → DC voltage (gap voltage) ； Vibration then has an AC component superimposed on it. 3. Measurement principles of various parameters: Axial vibration (radial vibration) – The probe is positioned perpendicular to the axis surface, and it measures the alternating variation in the gap (peak-to-peak value in μm). Typically, the X and Y axes are installed at 90° to form a combined axis trajectory.
Axis trajectory: Instrument-related issues such as loose probe installation, thermal deformation of the bracket, nonlinear gap voltage, and temperature drift; water ingress into cables/joints, reduced insulation, and changes in contact resistance. Pre-amplifier/card-related issues including zero-point drift and failed temperature compensation. Mechanical issues such as wear of thrust bearings, peeling of the bearing surface, warping of the thrust disc, uneven axial thermal expansion, and sticking of sliding pins. 4. Eccentricity abnormalities: Symptoms include high eccentricity at low speeds, excessive vibration during startup, and distorted axis trajectory. Instrument-related causes include eccentrically installed probes, vibrating brackets, and inappropriate gaps. Mechanical causes include bent rotors, high ellipticity, and worn shaft journals. 5. Loss or inaccuracy of rotation speed/key phase: Symptoms include no rotation speed, sudden changes in rotation speed, and loss of key phase pulses. Causes include the probe being too far from the keyway, excessive installation gaps, or incorrect orientation; shallow keyways or burrs, as well as an uneven shaft surface. Cable/pre-amplifier failures and interference can also be causes. 6. Temperature-related issues (bearing temperature): The principle involves using a Pt100 thermistor inserted into the temperature sensing hole of the bearing to measure its temperature. Common faults: open circuit (displaying above the upper limit), short circuit (displaying below the lower limit), poor contact (fluctuations), loose installation (low/uneven temperature). III. Quick judgment mnemonic (useful on-site): If there is no display, first check the voltage (-24V); then check the wires (for continuity/isolation); and finally check the probe (for resistance/gap). In cases of excessive vibration, first examine the trajectory: regular patterns suggest mechanical issues, while chaotic patterns point to instrument problems. For displacement drift, check for looseness, temperature issues, and water ingress at the connections. Loss of pulses in rotation speed is caused by three factors: gap, keyway issues, and wiring problems
II. Testing of the vibration instrument circuit: For 24V+OUT+COM, disconnect the OUT+ terminal and connect a signal generator to the circuit. Use a frequency signal of 50HZ, with input amplitude voltages of 0.1V, 0.4V, and 0.8V – these values correspond roughly to a measurement range of 0~200um. III. Testing of the phasor meter circuit: Connect the two signal wires of the phasor meter to the corresponding clips on the signal generator, set a voltage amplitude of 9V, and use input frequencies of 3HZ, 84HZ, and 165HZ – these frequencies roughly correspond to a range of 0~10000 rpm. IV. Testing of the speed meter circuit: Connect the two signal wires for speed to the corresponding terminals of the signal generator, set a voltage amplitude of 9V, and use input frequencies of 1HZ, 5000HZ, and 10000HZ – these frequencies correspond roughly to a range of 0~10000 rpm.
【Ten Years of Rapid Development in Chemical Engineering Equipment】From 2031 to 2026, CNOOC Engineering has mastered welding technology for ultra-high-strength steel at 865 MPa https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=5719034 (Source: Haichuan Chemical Industry Forum (HCBBS))