[time-nuts] Re: Long term stable environmental sensors (Attila Kinali)

[Neville Michie]

I have been using a variety of sensors and instruments over the last 50 years.
I do research on processes that occur in limestone caves and their atmospheres.
I also worked in a government research laboratory on developing measurement systems.
I stopped using dew point instruments because they were not suitable for ambient 
conditions. They have errors of fractions of degrees. Thin film sensors do no 
better that 1% RH and are not useable in the long term above 85-90% RH.
Sampling is a major problem in measuring environmental (air ) measurement.
I built a version of the WMO Reference Psychrometer, and I can measure air 
temperature in a cave to 0.01K and ) 0.1% RH (including 100%RH) for an average reading sample 
of 1m3 of air. These measurements preclude the presence of an observer.
Having taken the trouble to get consistent results in these stable conditions
I realise just how meaningless are the numbers that are bandied around of 
measurements in laboratories and work shops with active heat fluxes of kilowatts.
I use a four terminal Pt RTD with a 5 digit HP ohm meter, in a stirred thermostatic 
water bath to calibrate sensors, and an ice point cell to obtain a 10mK zero reference.
See: “Traceable Temperatures” J.V.Nicholas and D.R.White (1982) DSIR Bulletin 234, Wellington.
I built my own barometric sensors using altimeter capsules and an optical detection system.
I refer them to a laboratory grade Fortin Barometer.
When considering monitoring ambient conditions you must take account of radiation 
on the instrument and always remember that an error of 1 centigrade degree of air 
temperature causes anerror of ~10% RH.

Cheers, Neville Michie