Determining the accuracy of a weighing sensor requires a comprehensive assessment, including standard weight testing, zero-point and repeatability checks, linearity verification, and environmental stability evaluation, combined with an evaluation of its appearance, electrical parameters, and dynamic response.
Basic Inspection: Appearance and Electrical Parameters
Appearance Inspection
Check the sensor for mechanical deformation, cracks, impact marks, or water ingress and corrosion at the seals.
Check for cable damage, broken shielding, and loose terminals.
Measure key resistance values with a multimeter (using a common 4-wire strain gauge sensor as an example):
Input Impedance (Ex+ and Ex-): Normal value approximately 387Ω ±20Ω (e.g., Transcell SBS series).
Output Impedance (Sig+ and Sig-): Approximately 350Ω ±5Ω.
Insulation Resistance to Ground: ≥ 2000MΩ between any wire and the casing; below 500MΩ may indicate moisture damage or breakdown.
If the resistance value deviates significantly from the standard, it indicates that the internal strain gauge or circuitry is damaged.
Functional Test: Load Response and Signal Output
Measure Signal Change by Applying Excitation Voltage
Apply a 10V DC excitation voltage (red and black lines) to the sensor and measure the output terminal (green and white lines) with a high-precision multimeter.
The output should be close to 0 mV under no-load conditions (slight drift is permissible).
Gently press the sensor with your hand; the output should show a noticeable change (a few tenths of a second to a few mV). Otherwise, it may be damaged or the wiring sequence may be reversed.
Zero Point and Repeatability Test
Load the same standard weight (e.g., 50% of the range) multiple times and observe whether the instrument readings are consistent.
The maximum deviation of the three measurements should be ≤ 0.03% F.S.; otherwise, the repeatability is out of tolerance.
After unloading, check if the sensor can stably return to zero. If it continues to drift, there is a zero-point drift problem.
Linearity Verification
Use standard weights to progressively load the weights at 20%, 40%, 60%, 80%, and 100% of the range, recording the data.
Calculate the deviation from the ideal straight line at each point. A non-linearity error of ≤ 0.05% F.S. is considered normal.