I. Periodic Calibration (Preventative Judgment)
To ensure long-term stability, routine calibration is recommended at the following frequencies:
High-frequency use (≥3 times per week): Calibrate every 6 months.
Low-frequency use: Calibrate at least once a year.
New equipment or after repair: Calibration is mandatory before first use to ensure that factory accuracy is not compromised.
II. Performance Abnormalities (Fault Judgment)
When the following phenomena occur, it indicates that the instrument may be inaccurate and immediate calibration is required:
1. Inconsistent Test Results
If the test results for the same sample differ by ≥0.5 grades (e.g., dry friction drops from grade 4 to grade 3.5), after ruling out sample and operational factors, a problem with the equipment should be suspected.
2. Abnormal Friction Pressure
If the measured pressure deviates from the standard value of 9N±0.5N, the loading system can be verified using standard weights.
3. Inaccurate Stroke or Speed
The measured reciprocating stroke exceeds 100mm ± 1mm; the friction speed deviates from 60cpm (or the equipment's nominal value), which can be checked with a stopwatch or tachometer.
4. Large Counter Error
The actual number of runs deviates by more than ±1 when set to 10 friction cycles, affecting test repeatability.
5. Friction Head Wear or Deformation
Incorrect friction head size (circular Φ16mm, rectangular 19×25mm) or uneven surface will lead to uneven pressure distribution.
III. External Changes Triggering Calibration
The following situations also require recalibration to eliminate interference factors:
1. After equipment handling or vibration: This may cause internal structural loosening.
2. Changing the batch of friction cloth or the sample stage pad: If the test results show a systematic shift, it is necessary to confirm whether it is a problem with the equipment.
3. Recovery from Laboratory Temperature and Humidity Uncontrolled Operations: The standard environment is 20±2℃ and 65±4%RH. Environmental fluctuations may indirectly affect instrument performance.
IV. Standard Updates and Compliance Requirements
GB/T 3920-2024 has been released and will be implemented on January 1, 2027, fully replacing the old standard. The new standard imposes stricter requirements on friction head size, wet friction cloth liquid coverage, etc. Existing equipment must be calibrated in advance to comply with the new regulations.
Before customer factory audits, CNAS certification, or export audits, a valid calibration report must be provided to prove the traceability of the test data.
