How to inspect digital calipers for China Inspection and Quarantine, factory inspection and certification? Digital caliper inspection standards

Digital calipers, like vernier and dial calipers, are commonly used measuring instruments for precisely measuring length, inside and outside diameters, and depth. A high-precision rack on the caliper body drives the rotation of a circular grid. Using a photoelectric pulse counting principle, the displacement of the measuring jaws is converted into pulse signals, ultimately presenting the measurement results digitally on the display. Digital calipers offer clear readings, convenient operation, and a wide range of functions, making them widely used in industrial manufacturing and quality control. To ensure quality compliance, a systematic inspection and testing process is required.

1. Appearance inspection

During the inspection process, the digital caliper should first be subjected to a comprehensive appearance inspection , including but not limited to:

1. Surface condition inspection :
   The caliper surface must not have any defects such as cracks, scratches, bumps, rust, burrs, etc. that may affect its use or appearance.

2. Plated/coated surface inspection :
   The plating or coating should be uniform and firm, without any undesirable phenomena such as falling off and uneven color.

3. Ruler marking inspection :
   The ruler markings should be clear and continuous, without broken lines, uneven thickness or other defects that affect reading.

4. Display device inspection :
   The watch cover and display screen must be clean and transparent, without scratches, bubbles or other problems that may interfere with reading.

5. Movement and fastening performance test :
   The ruler frame and micro-motion device should move smoothly without sticking or loosening; the brake screw must be able to reliably fasten the ruler frame to the ruler body.

2. Technical requirements and inspection methods

During factory inspection or incoming material inspection , the following key indicators should be measured and verified according to the standards:

1. Measuring surface hardness test :
   Using a Vickers or Rockwell hardness tester, measure three points evenly spaced on the measuring surface or on the side within 2 mm of it, and calculate the arithmetic mean. The hardness of the digital caliper measuring surface should not be lower than the standard requirement for the corresponding material (carbon steel, tool steel, stainless steel).

2. Measuring surface roughness inspection :
   The Ra value should comply with the specified limit by visual comparison of roughness comparison specimens or inspection using a roughness meter.

3. Flatness and merge gap inspection :
   The flatness of the two outer measuring surfaces must meet the standards; in the combined gap inspection , the wide measuring surface should not be light-transmissive, and the narrow measuring surface of the blade should not be able to transmit white light.

4. Maximum allowable error test :

   • External measurement error: in line with the tolerance range specified for the corresponding accuracy level;

   • Measuring claw gap inside the blade: Use a 0.12mm feeler gauge to check , the gap must not be greater than this value;

   • Depth and step measurement error: The corresponding tolerance must also be met at the 20mm measurement point.

5. Repeatability test :
   Repeat moving the ruler frame 5 times to make the measuring surfaces contact. The maximum difference between the 5 measured values ​​should not exceed 0.010mm.

3. Performance Test

Performance inspection should be carried out under conditions simulating actual use, mainly including:

1. Digital display and response test :
   The display should be clear, stable and without flicker, and the response speed should be no less than 1m/s.

2. Function key operation test :
   All buttons must be flexible and reliable, with clear graphic labels and accurate functions.

3. Digital drift and power consumption test :
   Digital drift should not exceed 1 resolution value; operating current should not exceed 40μA.

4. Environmental adaptability test :
   The electronic digital display should operate normally under the conditions of 0°C–40°C and humidity ≤80%.

4. Communication interface inspection

If the product supports data output, communication interface inspection is required:

1. The manufacturer should provide supporting communication cables and software;

2. The communication cable should be able to achieve stable data transmission with universal interfaces such as RS-232 and USB.

V. Inspection conditions

All inspection operations should be carried out under the following environmental conditions:

• Temperature: 20°C ± 5°C

• Humidity: ≤80% RH
  Ensure that inspection results are accurate and reliable.

VI. Marking, packaging and compliance inspection

During the final inspection stage, product labeling and packaging should be systematically checked :

1. Product mark inspection :
   The caliper body must be marked with the manufacturer's name/trademark, resolution, and product serial number, and stainless steel material must have an identification mark.

2. Packaging mark inspection :
   The manufacturer's name, product name, resolution and measuring range should be clearly indicated on the packaging box.

3. Rust prevention and packaging integrity inspection :
   The product must be treated with rust prevention and the packaging should be firm and reliable to ensure no damage during transportation.

4. Certification and compliance testing :
   Each qualified product should be accompanied by a certificate of conformity, marked with the standard number, product serial number and production date, to complete the final inspection and access.

7. The service value of third-party inspection

When it comes to high-precision measuring tools like digital calipers, companies can rely on professional third-party inspection companies to carry out the aforementioned inspection process. Their services typically include factory assessments, in-process testing (IPC), finished product inspection (FRI), and shipment monitoring. Leveraging standardized inspection methods and testing equipment, they ensure that products comply with technical specifications and national/international standards throughout the entire production and delivery process, effectively mitigating quality risks and improving supply chain quality control.

We at China Huibang Focus specialize in product inspection and quarantine, testing and certification, supplier background checks, audits, factory inspections and other services.