During gas generator repair, calibrating the speed sensor is a critical step in ensuring stable engine operation and optimizing performance parameters. As a core component of the gas generator control system, the accuracy of the speed sensor's output signal directly affects ignition timing, fuel injection volume, and load regulation. Therefore, precision calibration requires a systematic process.
Preparatory work before calibration requires environmental control and equipment inspection. Maintenance personnel should select a location away from strong electromagnetic interference sources to prevent electromagnetic noise from equipment such as inverters and high-voltage lines from interfering with the sensor signal. The sensor should also be inspected for cracks, oil stains, or metal debris, as these foreign objects can cause signal attenuation or waveform distortion. For magnetoelectric sensors, the gap between the probe and the gear plate must be confirmed to be within the manufacturer's specified range of 1mm ± 0.2mm. Excessive gaps can reduce the induced electromotive force, while too small gaps can cause mechanical wear.
Basic resistance testing is the primary step in determining the sensor's physical condition. Use a digital multimeter to measure the DC resistance between the sensor's two leads. A typical value is between 0.7kΩ and 1.2kΩ. If the measured value falls outside this range, it indicates an open or short-circuited coil, requiring immediate sensor replacement. For example, if the internal Hall element of a Hall effect sensor is damaged, the resistance value may be abnormally infinite or near-zero. Calibration alone cannot correct this fault.
For waveform analysis, an oscilloscope is required to capture the sensor output signal. Connect the oscilloscope probe to the sensor signal line, start the gasoline generator, and maintain idle speed to observe the waveform characteristics. A normal waveform should be a stable square wave or a near-sine wave. Missing teeth, glitches, or amplitude decay may be caused by target wheel deformation, sensor mounting misalignment, or poor signal line contact. Check the target wheel tooth profile for integrity, sensor mounting bolts for looseness, and shield grounding for reliably secure connection.
Dynamic calibration requires the use of a speed reference device. The sensor to be calibrated and a reference tachometer are installed simultaneously on the engine test bench. The engine speed is gradually increased from the lowest stable speed to the rated speed using a frequency converter. Pause for 30 seconds at each calibration point and record the sensor output value against the reference value. Data comparison is performed using the synchronous counting and timing method. By simultaneously measuring the signal period and count pulses, this method eliminates the ±1 error of the fixed counting method at low speeds and the ±1 time unit error of the fixed counting method at high speeds, achieving a calibration accuracy of 0.05% across the entire speed range.
Parameter correction requires targeted adjustments based on the error type. If the sensor exhibits linearity error, manifesting as a proportional deviation between the output value and the actual speed, this can be compensated by programming a correction factor. For sensors with hysteresis error—that is, the difference in output value at the same speed point during acceleration and deceleration exceeds the allowable range—the threshold parameters of the sensor's internal signal processing circuitry must be adjusted. Some smart sensors support software parameter updates via the diagnostic interface, simplifying the calibration process.
The final verification phase requires complex testing simulating actual operating conditions. Connect a gasoline generator to the load cabinet and gradually increase the load to 80% of the rated power while monitoring the sensor output stability. During transient load increases and decreases, the sensor signal fluctuation should not exceed ±2%. If abnormalities persist after calibration, check the engine's flywheel ring gear for deformation or interference in the ECU interface circuit. If necessary, replace the sensor and recalibrate.
The entire calibration process must strictly adhere to the closed-loop principle of "test-analysis-correction-verification" to ensure that the speed sensor's output accuracy is better than ±1% across the entire speed range of the gasoline generator. Regular calibration not only extends the sensor's lifespan but also prevents engine surging, excessive emissions, and other related failures caused by speed signal distortion, providing a fundamental guarantee for the reliable operation of the gasoline generator.
