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Metrology for the 2020s - a beginner's guide

When we asked people what they thought of our vision of Metrology for the 2020s the response was overwhelmingly positive, but a comment was made that it would help if we also produced something for those new to metrology - the science of measurement.

### You know a lot about metrology but just didn't realise it

You don't have to be a technical expert, metrologist or quantum physicist to understand our ideas of where 'measurement' is going.

Measurement is something that most people are familiar with, either personally - how tall they are or how much they weigh - or by performing everyday activities, like filling your car with fuel or weighing vegetables in the supermarket.

And we all know a bit about how measurements work: we need units (height in metres), some kind of instrument (a tape measure) and we follow a method of using this instrument (making a mark on the wall at the top of your head and measuring up from the floor to this mark).

### Uncertain measurements

When making a measurement, you are trying to find the 'real' value of something. You need to understand how close to this value you are likely to get, without knowing what the real value is – we call this understanding the uncertainty.

In the height measuring example, to reduce uncertainty you would need to:

• make sure you know exactly how long a metre is (what is the definition of the metre)
• ensure that the tape measure scale is based on this idea of how long a metre is (make sure tape measure is traceable to the metre and the scale is calibrated)
• think about what could introduce a variation that affects the precision and accuracy and eliminate them, for example, the angle of the pencil when you draw the line or wearing different shoes each time (standardise the measurement)

Metrology is the science of making measurements to reduce this uncertainty.

This is in action every day across society, for example when:

• ensuring that car and aircraft parts made in different factories throughout the world all fit together
• ensuring that chemical processes are running at the right temperature
• making measurements on cells to support biology research
• ensuring that patients being treated for cancer receive the correct dose of radiation to kill the cancer without too many side effects

### NPL and the new metrology

NPL is the UK's National Measurement Institute, specialising in the understanding of metrology and helping people reduce the uncertainty of their measurements.

It takes time to create new measurement knowledge and put it in the hands of users. Metrology for the 2020s is NPL's view of how metrology will need to develop to be useful to society in the 2020s. It has four elements, which are outlined below.

The Quantum SI

The best way to make sure that everyone uses the same units of measurement is to standardise them on something that we know will not change - for example the speed of light in a vacuum. This is known as a fundamental constant of nature and is currently used for what metrologists call the 'definition' of the metre, which is how far light travels in a very small fraction of a second.

The use of these constants in this way has been given the name 'Quantum SI' as many of these are the basis for quantum physics.

The Quantum SI is better because:

• The uncertainties in the units are much smaller than when using physical artefacts
• It is based on fundamentals that are true all over the world, and the universe, and can be realised without having the artefact
• The units can be related to each other to give a cross-check and produce a better system of units

At the moment these Quantum SI units are being realised in special laboratories but in the future they will be available more widely on computer chips or within equipment that is portable rather than taking up a whole laboratory.

Measurement at the frontiers

People have been making measurements for a long time and have become very good at it, but challenges still remain even in areas where we have experience. We need new measurements and, as technology develops, we also need to reduce the uncertainties, for example:

• The roughness or texture of the surface of an object can be measured very well over a small area but this is very difficult and slow to do over a larger area such as an aircraft wing - the need to improve aerodynamics drives the surface technology development and the metrology now needs to improve.
• To reduce the environmental impact of jet engines the materials used to build them need to be very well understood and the environment inside the engine precisiely controlled so that it runs at the optimum conditions. We can measure the properties, chemistry and structure of materials very well in laboratories, but it is far more challenging to do so inside a jet engine.
• We need to understand exactly what dose of radiation or ultrasound a tumour receives during cancer treatments using a method that does not affect the surrounding healthy tissue. The technology and method to deliver the radiation has improved so the measurements also need to improve to help achieve the best outcome for the patient.

Smart and interconnected measurement

We are all familiar with making single or 'spot' measurements, like measuring your height. You make one measurement at one place, at one time, using one instrument to get one number. But the ability of new communications technologies to connect up a large number of sensors and the availability of computing power to crunch the numbers means we can make measurements differently.For example:

• Measuring atmospheric chemistry and pollution using a network of sensors to produce a map of the area and combining this with measured traffic flows in the road systems in order to help manage the peak pollution levels.

Embedded and ubiquitous measurement

Measurement sensors are becoming smaller and cheaper as manufacturing technologies improve. They can be incorporated into devices, tools, clothes or mobile phones to do new things or vastly improve on the way we do things now, for example:

• Manufacturing tools with built in sensors that adapt to changes in the raw material or wear and tear in the machine to produce perfect products every time - improving quality and reducing waste.
• A workforce of robots that can sense each other's presence and work cooperatively by knowing their exact position, by monitoring the forces on robotic arms and hands, for example in hostile chemical or radioactive environments, where human safety cannot be guaranteed.
• Sensors built into food packaging that monitor the condition of the food rather than using a sell-buy date - they then automatically transmit a signal to a control system if action is required - saving waste and reducing the risk of health problems.