The methods for determining the quality of electronic scale sensors are as follows:
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1. Visual Inspection
- Check if the sensor casing is deformed, cracked, corroded, or damaged; any bending of the elastomer exceeding 0.1mm per meter is considered abnormal.
- Inspect the terminal connections for oxidation or looseness, check for any broken or damaged cables, and look for condensation inside the protective cover (humidity > 60% accelerates aging).
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2. Resistance Measurement
- After disconnecting power, use a multimeter to measure the input resistance (exc+ to exc-) and output resistance (sig+ to sig-) of the sensor. Normally, the input resistance should be ≥ output resistance > bridge resistance, and the bridge resistances should be equal or pairwise equal.
- If there is no manual, compare parameters by measuring several sensors or refer to the common resistance range of sensors (e.g., input resistance around 380Ω, output resistance around 350Ω, with an error of < 5Ω).
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3. Voltage Measurement
- When powered on, measure the excitation voltage between the instrument terminals exc+ and exc- within the DC voltage range of the multimeter; it should normally be 5-10V.
- With the device unloaded, measure the output voltage of the sensor signal terminal (sig+ to sig-), which should be close to 0 and less than the maximum output of the sensor (maximum output = excitation voltage × sensor sensitivity, sensitivity is generally 2mV/V). If the unloaded voltage exceeds the range (e.g., showing above 34mV), the sensor may be damaged.
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4. Load Testing
- Gradually load standard weights (e.g., 20%, 40% of full scale), recording the output signal for each weight value, which should show linear variation.
- If the non-linearity error exceeds 0.05% or the difference in repeated loading exceeds 0.03%, the sensor needs to be replaced.
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5. System Isolation Method
- Disconnect each sensor connection one by one; if connecting a certain sensor shows abnormal readings (e.g., jumps or alarms), that sensor is deemed faulty.
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6. Oscilloscope Monitoring
- The normal signal should be a stable step waveform with a rise time < 5ms; spikes or oscillations indicate poor contact or damping failure.
If a sensor is confirmed to be damaged, it should be replaced with a product of the same model and specifications, and the electronic scale should be recalibrated.
