Torque wrenches go out of calibration with use. Verifying the accuracy of a torque wrench is a key quality measurement that must be taken for a successful outcome. Two accepted methods may be used. Verification is a process step to validate if the wrench is in or out of calibration. This test can be conducted with a suitable torque tester/checker. Any operator or inspector may verify a wrench by connecting it to a suitable torque tester and pulling the wrench. The torque tester will display a result that must be compared to the allowable tolerance of the wrench. Some torque testers offer a tolerance-setting feature that provides a GO/NG result (RED or GREEN) when the wrench is pulled. If the verification result is OK then the wrench is deemed in tolerance. If it is NG then calibration or adjustment of the wrench is required.

Unless broken, calibrating a torque wrench is a fine-tuning of the wrench to bring it back within tolerance. A competently trained technician with equipment that is certified to the National Institute of Standards and Technology (NIST) must perform the work if a calibration certificate is required. The international standard for torque wrench calibration (ISO6789) mandates all conforming wrenches meet or exceed 5000 cycles before requiring calibration. It also defines the methodology for calibration. Most competent wrench manufacturers use ISO 6789 as the basis for establishing performance criteria or standards for their tools.

A regular scheduled verification and calibration program helps to eliminate errors based on a wrench being out of tolerance. Competent calibration labs in conformance with ISO17025 or best practices will issue “as found” readings for a calibration, allowing examination of the wrench condition at time of calibration. It is an industry practice to reduce the calibration interval by one half if a wrench is found to be out of tolerance at time of calibration. Failure to calibrate a torque wrench may lead to failure of a joined connection.

Torque measurement is utilized in three areas of assembly. Controlling torque is quintessential for companies to ensure their product’s quality, safety and reliability isn’t compromised.

Prior to Assembly
Torque testing equipment, like electronic torque tester and  torque sensors are used before assembly process for tool setup or conducting tool capability studies. For tool setup, the tool crib will want to set the torque tool according the torque specification required for the application. For tool capability studies, technicians need to ensure that the torque tool can provide the necessary torque and repeatability that’s required for a potential application.

The equipment used for this torque testing would be:
- Tabletop torque testers with built-in transducers
- Torque analyzer that connects with either stationary torque sensors or rotary torque sensors
- Joint simulators like run down adapters

During  Assembly
For air and electric assembly tools once the torque tool is being used in the production area, many manufacturers like to audit the tool and verify the actual torque being applied to the application or if the tool is starting to fall out of specification. The Rotary Torque Sensor is the ideal torque-auditing tool for testing the actual torque being applied on the assembly application. By connecting a rotary torque sensor between an electric or pneumatic tool and assembly application, you can monitor the torque being applied from the tool to fastener or bolt. This type of torque reading is called a dynamic torque reading. The rotary sensor is connected to torque analyzer, which records and stores the data.

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