Development of a Standard Practice for the Calibration of Torque-measuring Instruments for Verifying the Torque Indication of Testing Machines Speaker/author: Gary Dahlberg MTS Systems Corporation 1581 Gros Ventre Dr. NE Rio Rancho, NM 87144 gary.dahlberg@mts.com Frequently, presenters must deliver material of a technical nature to an audience unfamiliar with the topic or vocabulary. The material may be complex or heavy with detail. To present technical material effectively, use the following guidelines from Dale Carnegie Training®.   Consider the amount of time available and prepare to organize your material. Narrow your topic. Divide your presentation into clear segments. Follow a logical progression. Maintain your focus throughout. Close the presentation with a summary, repetition of the key steps, or a logical conclusion. Keep your audience in mind at all times. For example, be sure data is clear and information is relevant. Keep the level of detail and vocabulary appropriate for the audience. Use visuals to support key points or steps. Keep alert to the needs of your listeners, and you will have a more receptive audience. Copyright 2002, MTS Systems Corp.

ASTM American Society for Testing and Materials International Over 11,000 testing standards used by industry, government, and universities. Testing standards covering a wide range of testing in support of the transportation, medical, and consumer goods industries. Committee and subcommittee members include representatives from testing machine manufacturers, testing laboratories, government agencies, and universities. In your opening, establish the relevancy of the topic to the audience. Give a brief preview of the presentation and establish value for the listeners. Take into account your audience’s interest and expertise in the topic when choosing your vocabulary, examples, and illustrations. Focus on the importance of the topic to your audience, and you will have more attentive listeners.

ASTM Subcommittee E28.01 on Calibration of Mechanical Testing Machines and Apparatus E74 – Calibration of force-measuring instruments for verifying the force indication of testing machines. E4 – Standard Practices for Force Verification of Testing Machines. E83 – Standard Practice for Verification and Classification of Extensometers. Additional standards in process: Standard Practice for Calibration of Torque-Measuring Instruments for Verifying the Torque Indication of Torque Testing Machines. Standard Practices for Torque Verification of Torque Testing Machines. Standard Practices for Verification of Displacement Measuring Systems and Devices used in Material Testing Machines. If you have several points, steps, or key ideas use multiple slides. Determine if your audience is to understand a new idea, learn a process, or receive greater depth to a familiar concept. Back up each point with adequate explanation. As appropriate, supplement your presentation with technical support data in hard copy or on disc, e-mail, or the Internet. Develop each point adequately to communicate with your audience.

The need for a new Standard! Testing machines are being used to measure and apply known torsional forces to specimens and or components in order to determine reliability and durability of materials. Accreditation pressures are adding important emphasis on the need for verifiable measurement uncertainty related to testing results.

Developing the Calibration Standard Identify and document the requirement and submit for a designation number from ASTM. Establish the specifications. Investigate available traceability standards and organizations. Investigate and compare other approved standard practices. Draft the practice. Initiate a Round Robin Testing program to support the practice. Ballot the standard.

European Standards BS 7882 – Method for Calibration and classification of torque measuring devices. DIN 51309 – Material testing machines, Calibration of static torque measuring devices.

BS 7882 Classification Criteria Maximum permissible error of the torque measuring device %   Relative Error of repeatability reproducibility Relative error interpolation of zero reversibility Relative error of indication 0.1 0.05 0.10 ± 0.05 ± 0.02 0.125 0.2 0.20 ± 0.10 ± 0.04 0.250 0.5 0.25 0.50 ± 0.25 0.625 1.0 1.00 ± 0.50 ± 0.20 1.250 2.0 2.00 ± 1.00 ± 0.40 2.500 5.0 2.50 5.00 ± 2.50 6.250  

BS 7883 – Uncertainty of Calibration Torques Class of torque measuring device to be calibrated Maximum permissible uncertainty of calibration torque applied (BS 7882) 0.1 ± 0.02 0.2 ± 0.04 0.5 ± 0.10 1.0 ± 0.20 2.0 ± 0.40 5.0 ± 1.00

DIN 51309 Classification Criteria Calibration Torque Maximum permissible error of the torque measuring device in % Class Relative reproducibility error repeatability error of zero signal reversibility Relative error of indication or interpolation Min value of measurement range Expanded rel. uncertainty of measurement in % (k=2) 0.05 0.025 0.0125 0.063 ±0.025 ≥ 4000 r 0.010 0.1 0.10 0.125 ±0.05 ≥ 2000 r 0.020 0.2 0.20 0.050 0.250 ±0.10 ≥ 1000 r 0.040 0.5 0.50 0.25 0.63 ±0.25 ≥ 400 r 1 1.0 1.25 ±0.5 ≥ 200 r 2 2.0 2.50 ±1.0 ≥ 100 r 0.40 5 5.0 6.25 ±2.5 ≥ 40 r (r = resolution)

ASTM Classification Criteria Class AA – Measurement uncertainty not to exceed 0.05% of moment torque. The lower torque limit is defined as 2000 times the uncertainty in torque units derived from the calibration data. Class A – Measurement uncertainty not to exceed 0.25% of the moment torque. The lower torque limit is defined as 400 times the uncertainty in torque units derived from the calibration data.

Similarities between European and ASTM practice/methods Attention to alignment and fixturing. Monitoring and control of laboratory temperature. Determination of resolution. Preloading conditions. Application of torsional forces. Recalibration is required anytime the device is subject to excessive overloading and or repair, or when ever the uncertainty of the device is in question.

Differences between European and ASTM practice/methods European standard provide additional classification tiers. European standards allow for classification of devices other than those devices used for calibration and verification of testing machines. ASTM practice does not require a run of repeatability data with the device in an unchanged mounting position. European methods require 30 second stability times for acquisition of data with torsional forces applied and at zero torque. ASTM standard recommends annual recalibration and not to exceed 2 years intervals after the first year. The standard provides some guidance for lengthening the calibration interval. BS 7882 – States that recalibration be performed at least every 12 months. DIN 51309 states that the maximum period of validity of the calibration certificate shall not exceed 26 months.

ASTM and European Standards These standards do not address “As-Found” calibration data. There is no stability criteria over time. Or comparison of present to past calibration data.

Round Robin Testing Program PTB (Physikalisch-Technische Bundesanstalt) – Served as Reference Laboratory (NIST does not have a torque standard). Dave Kreitlow from the MTS Systems Corporation Metrology Laboratory served as technical advisor. MTS also provided the artifact. NAPT (National Association for Proficiency Testing) – Served as Round Robin/Proficiency Testing Administrator. 9 Laboratories participated.

Artifact

Reference Laboratory - PTB

Round Robin Results Clockwise

Round Robin Results Anti-Clockwise

Conclusions The practice will benefit from having measurement uncertainty included as it is in the European standards. The data shows that laboratories using the standard can produce credible data with good interchangeability between laboratories. The standard will be acceptable for balloting with minor changes.