Measurement performance of tensile testing machineIt is the fundamental prerequisite for ensuring the accuracy and reliability of all material mechanics testing data. Regular calibration can not only verify the equipment status, but also meet the requirementsISO/IEC 17025The requirements of the laboratory management system are the foundation for product quality control, reliable research and development data, and trade arbitration. This article will systematically explain the core items, standard procedures, and key practical methods of calibration for electronic tensile testing machines.

The necessity and core objectives of correction

As a precision force measurement system, the electronic tensile testing machine's sensors, transmission mechanism, and measurement circuit may experience slight performance drift over time, frequency of use, and environment. Uncorrected equipment may display force values, displacements, and velocities that deviate from the true values, leading to misjudgments of material properties. for example, inStretch strength of packaging film, peel strength of adhesive or breaking strength of textileIn testing, even a few percent deviation may result in qualified products being judged as unqualified or conceal real quality issues.
Therefore, the core goal of calibration is to compare and contraststandard instrumentQuantify and confirm the known values of the testing machine systematicallyindication errorIs it within the allowable range (such as force value ± 1%), ensuring that its measurement results can be traced back to national or international measurement standards.

Core calibration projects and cycles

The calibration of electronic tensile testing machines mainly revolves around two basic and independent parameters:

• Force value (load)The accuracy of the measurement system's indication at different load points (such as 20%, 50%, 100% of full scale).

• Displacement and velocityIncluding the movement of the crossbeamTravel accuracy(Displacement) and at the set speedSpeed stability(Speed).
  The recommended regular calibration cycle isa yearHowever, temporary calibration should be carried out immediately when the equipment undergoes major repairs, moves to a new installation location, or when there are doubts about the test data.

Standard calibration procedures and methods

The following calibration operations should follow metrological standards and be carried out in a stable laboratory environment.

1. Force correction
Force correction requires the use of qualified instruments that have been verified by higher-level metrology institutionsstandard force gaugeOr a groupstandard weight.

• Principle and OperationInstall the standard force gauge between the upper and lower fixtures of the equipment, or hang the standard weight in the prescribed manner. Start the tensile machine and apply a series of increasing target force values to the standard, while recording the standard value of the standard and the displayed value of the tensile machine separately.

• data analysisCalculate the value of each calibration pointrelative error(Display value standard value/standard value x 100%) andindication repeatabilityThe core requirement is that the error and repeatability of each point should meet the established accuracy level (such as within ± 1.0%).

2. Displacement and velocity correction
This project is used to verify the accuracy of the equipment control system.

• Displacement correction: Can be usedStandard displacement block gaugeorlaser interferometerSet the device to move a specific theoretical distance, measure the actual displacement with a standard, and calculate the error.

• 速度校正Usually combined with displacement correction. Set up equipment toSpecific speed (such as 100 mm/min or 500 mm/min)Run for a specified period of time (such as 1 minute), measure the actual displacement and calculate the average velocity to verify its deviation from the set value.

3. Overall system verification (simple daily method)
Between two formal calibrations, known performance can be usedStandard reference materials(such as standard rubber or metal splines) for quick verification. Regularly testing the standard spline and comparing its historical data range of tensile strength, elongation, and other results can effectively monitor the sustained stability of the equipment.

Correlation considerations and instrument selection for calibration

Standardized calibration practices are closely related to the early selection of equipment. A well-designed tensile testing machine that emphasizes long-term stability not only allows for easier calibration, but also provides more comparable data throughout its entire lifecycle. For example, choosing to useHigh stability strain gauge sensor, precision ball screw transmission, and closed-loop servo control systemThe device has smaller performance drift and higher reliability within the calibration cycle.
In addition, for customers with special testing requirements, if testing is neededPackaging material heat sealing strength, adhesive adhesion or textile bursting performanceWhen choosing a host, more attention should be paid to its fixture compatibility, expansion interface, and whether the control software complies with relevant testing standards (such as GB/T, ASTM, ISO, etc.), which lays the foundation for future diversified precision testing.

Common Technical Q&A

1. Q: Can companies purchase standard weights for force calibration on their own?

   Answer: The use of standard weights for "hanging weight method" calibration is only applicable to specific models with a small range and a vertical downward force direction. For the vast majority of commonly used electronic tensile testing machines, the performance of their force sensors varies between tensile and compressive states, and professional standard force gauges must be used to perform multi-point calibration under simulated actual testing conditions.It is recommended to entrust the regular formal calibration work to a third-party metrology institution with CNAS qualificationsTo ensure traceability of calibration. Self operation may not guarantee effective results due to improper methods.

2. Q: The calibration report shows that the displacement error exceeds the standard. What could be the possible reason? How does it affect testing?

   Answer: Displacement error exceeding the standard is usually due toScrew wear, encoder malfunction, or transmission system clearanceof This will result in the materialElongation rate and elastic modulusFundamental errors occurred in the calculation of key parameters. For example, when testing the elongation at break of paper or the yield strain of plastic film, inaccurate displacement will directly result in invalid results. If this problem occurs, the equipment supplier should be contacted immediately for mechanical maintenance.

3. Q: Does laboratory temperature and humidity have an impact on the performance and calibration of tensile testing machines?

   Answer: It has a significant impact. Changes in temperature and humidity can cause zero drift and sensitivity changes in sensor circuits, as well as thermal expansion and contraction of mechanical components.All precision calibration and testing should be conducted in a standard temperature and humidity environment (such as 23 ± 2 ° C, 50 ± 10% RH)And indicate the environmental conditions in the report. This is also one of the reasons why state adjustment is necessary before sample testing.

4. Q: We mainly test the peel strength of aluminum foil packaging for the pharmaceutical industry. What are the special precautions for calibration?

   Answer: The pharmaceutical industry has high requirements for data integrity and compliance. In addition to conventional force and velocity correction, special attention should be paid toDoes the device control software meet the requirements of regulations such as 21 CFR Part 11 for electronic data and audit trailsIn the selection of calibration services, priority should be given to suppliers who can provide calibration certificates that comply with GMP/GDP standards, ensuring that the entire chain from equipment, calibration to data generation is traceable and controlled.

DisclaimersThe purpose of this article is to introduce the general principles and conventional practices of calibration for electronic tensile testing machines, for technical exchange and reference only. The specific calibration operation must strictly follow the technical manual of the equipment manufacturer, the National Metrological Verification Regulations (JJG), or the calibration specifications recognized by both parties. Formal metrological verification/calibration activities should be carried out by institutions with corresponding qualifications and capabilities.