I’m starting a new thread on something David Holstius referenced “Blind Calibration” (BC) in “Calibration Gas (NO2) sensors”
The reference is
And I posted what I decoded from the paper and then thought it would be a good opportunity to discuss it on a separate thread, as it is the most coherent framework that I have heard of so far for .
It seems to me though that Balzano (UCLA) and Nowak(U.Wisc) haven’t covered the fundamentals of measurement theory.
So I’d like to explore my understandings of it here, and if anybody has some thoughts to jump in.
The BC use temperature, and so I would like to start with that – since everyone has a “feeling” for temperature and at the same time has the experience of translating between a number of world views of temperature (Fahrenheit Celsius Kelvin).
There are a number of references scales of temperature Fahrenheit, Celsius/Centigrade and Kelvin.
They all have a direct linear relationship to each other, and all have been successful in their own domain.
The Fahrenheit scale evolved by German physicist Daniel Fahrenheit (1686-1736)– proposed in a paper in 1724 was based on his perception of calibration points.
The Celsius scale named after Aders Celsius (1701-1744) used an SI notation of 100 divisions between freezing point of water and boiling point of water.
The Kelvin scale named after William Thomson Kelvin (1824-1907) references an absolute zero, and a unit of degree Celsius.
The absolute zero is equivalent to -273C.
Subsequent analysis has resulted in refinement of the definitions, and national standards to maintain those definitions to the degree of accuracy required by scientific (& economic) standards .
So my understanding is that fundamentals of a scale are defined.
They could be anything – but a system is chosen and widely/taught.
In the case of temperature- the core definitions is two physical transition states of water – boiling point of water, melting point of pure ice – and a scale defined with a 100 units called Celsius between the two points.
Measuring temperature is so economically & scientifically valuable – and a fundamental energy property of the universe that all sorts of methods of been discovered to transform the real world energy to a measurable temperature scale.
From expansion of alcohol (and mercury) in a narrow capillary tube, to properties of materials (thermistors, thermocouples) that can be measured electrically.
As modern history shows it doesn’t matter too much what scale is used (Fahrenheit in the public forums of the US – Celsius in the rest of the world) – so long as everyone understands what scale is being used and when there is a need to translate.
An alcohol thermometer doesn’t have a natural relationship to freezing point of water – it has a constructed relationship – usually over a scale that its target market wants. Eg healthcare
A thermistor is a type of resistor who’s resistance varies significantly with temperature – and is engineered and characterized to have electrical properties that can then be mathematically transformed to units of temperature – your choice.
What I’m detailing for temperature is there is traceability back to the two fundamental transition points of water, and a arbitrary scale of 100units between those points
Now looking at another common set of measurements – length – say 1meter or 1foot – a ruler, or tape measure – they all essentially have two points - a beginning – ‘0’ units – and an end. 1m or 1ft. They have units to make it useful. Metric or imperial.
Eg for NO2 with a range of interest between 0ppb and 250ppb for any given volume
So the molecular science for a constant 1 liter (or scaled appropriately) there would be 6.02214X×10**23. Molecules (or elementary entities of Synthetic Air)
So for 0 ppb NO2 – or possibly including measurement error purpose less than 0.5ppb of NO2 – 0.5*6.02214X×10**14.
So for there to be 250ppb of NO2 in 1L this would be 250*6.02214X×10**14
If we could snapshot a volume and then have an molecular counter – then it would be possible to directly relate counted molecular in a given volume to the parts per billion in that volume.
However the MiCS2710/2714 innovative low cost NO2 sensor - defines that it has a physical property of resistance that is proportional to the ratio of NO2 on its surface best measured at 220C – and further more it explicitly states for absolute measurements, interpret from my resistive scale at least two measurements.
One synthetic air – giving a 0ppb on its scale
And another one of the designers choice – say 100ppb or 250ppb.
So coming back to blind calibrations from raw sensors – I think the papers are missing a fundamental description of measurement theory.
I’d really like to hear from anybody investing the computational side if I have missed something.