NPL is home to the UK's national force standards – a set of seven machines used to generate precisely‑known forces in the range from 25 N to 30 MN. The most accurate of these are our four deadweight machines which use the Earth's gravitational pull on calibrated masses to realise forces with an uncertainty of 0.001 %. The largest of these can generate forces of up to 1.2 MN. Above this range, we generate forces hydraulically in machines with capacities of 5 MN, 12 MN and 30 MN. The machines are used to calibrate force-measuring devices which are then used in industry to make accurate and traceable force measurements.
The 1.2 MN machine was designed and manufactured in the 1980s. A major programme to replace its control system, both software and hardware, is under way. The opportunity is also being taken to improve certain aspects of its operation, including:
The 5 MN and 12 MN machines were constructed in the 1960s and 1970s respectively. Their current performance (a generated force uncertainty of 0.05 %) is at the upper limit of what UK industry requires.
We are continuously improving and reviewing our facilities and services within this force range by developing a new hydraulic machine resulting in the following improvements:
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