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Setting the standards for torque calibration

11 March 2011

Norbar’s calibration laboratory in Banbury is widely claimed to be setting the national standard for torque calibration. This expertise has developed over 20 years and underpins the work of the company worldwide. Barry Pratt reports

The resources for accurate and traceable torque measurement are vital to support the UK’s world leading position in precision engineering. When the National Physical Laboratory (NPL) sold the UK national torque standard to USA interests, an important reference standard for torque went overseas and arguably an asset to British engineering has been let slip without sufficient assessment of the consequences.

The sale of this standard has left a vacuum that has led to Norbar Torque Tools being increasingly approached by manufacturers as the de facto UK reference point for torque measurement. This is mainly because the work of the company’s calibration laboratory is internationally known and respected.

Its capabilities are also being continually developed. Recently, it achieved UKAS (United Kingdom Accreditation Service) accreditation for performing calibrations up to 108,500Nm of torque under BS7882:2008. At the other end of the scale the laboratory handles delicate calibrations down to 0.005Nm.

The Norbar laboratory is the only facility in the UK able to perform this range of UKAS accredited calibrations, providing the UK’s lowest available uncertainty of applied torque at ± 0.02%. Of the 18 people who currently work in the laboratory, 14 are UKAS specified staff.
Norbar has been producing torque calibration equipment for over 60 years and designs and manufactures its own tools and equipment with which they are produced.

The UK calibration laboratory has existed in one form or another since 1969 and the accredited facility was established in 1989, starting with the calibration of torque wrenches and transducers and then progressing to the development of measurements for torque multipliers, calibration beams and electrical torque indicators.

The company also develops and manufactures its own transducers to calibrate torque wrenches and designs and produces the calibration beams to calibrate the transducers. The whole process is therefore subject to in-house control.

The competence of calibration laboratories falls under the international standard ISO/IEC 17025:2005 which provides the benchmark for their performance. ISO/IEC 17025:2005 covers testing and calibration and is an essential tool for laboratories to develop their management system for quality, administration and technical operations. The standard is used by accreditation bodies such as UKAS as the basis for evaluation. Customers also recognise the importance of this standard as a qualification of the laboratory’s competence to deliver technically valid results.
Maintaining this standard is a continual process of assessment and inspection for calibration laboratories, and Norbar is audited annually by UKAS and has a full reassessment of its quality system every four years. The independence of UKAS is an important factor because it gives end users the confidence to invest in products without feeling the need to conduct their own audits.

Norbar calibrates other manufacturers’ products as well as its own, and over the last 12 months this accounted for 11% of the laboratory’s work. More torque calibration certificates to BS7882 are issued by this Banbury based laboratory than any other facility in the world and over the same 12-month period it issued over 8,000 certificates.

Quality control checks underpin the entire process and traceability is assured. The laboratory will, where possible, also match its procedures to specific customer specifications.

Since the UK facility was set up, Norbar has established accredited calibration laboratories at its company offices in Australia, China, Singapore and the USA. As a policy, this is one of its first priorities when setting up a branch overseas and underpins the quality of the company’s products.

One of the recent co-operative projects the company has carried out is torque comparisons on 10Nm, 100Nm, 1,000Nm and 5,000Nm transducers with its laboratories overseas. Results have been compared against the UK national standard and detailed reports compiled. This exercise is an invaluable method of ensuring the equivalence of calibration and quality world wide.

Norbar’s commitment to accreditation via Recognised Accreditation Bodies ensures that the certificates issued by any of its laboratories are accepted as equivalent in many countries. This is an important aspect of product quality assurance to facilitate international trade.

Various new developments are currently taking place at the UK laboratory, including electronic data transfer to speed up the certification process, and the design of second generation calibration beams offering enhanced performance.

Barry Pratt is head of laboratory, Norbar Torque Tools

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