TOT - digital thermometers in clocks/weather stations

Just bought another indoor/outdoor thingie in the Lidl sale as my previous purchase kept losing the connection with the outdoor sender.

I now have four tempreature sensors lined up in the shade on the dining room table and they all give diffferent results.

My 'control' is a digital radio controlled clock made by TCM which seemed to match the aircon maintenance handheld thermometer most of the time when I had it at work so is possibly fairly accurate.

I will give them longer to stabilise - I note that on my latest purchase the outdoor temperature semsor updates more quickly than the indoor one.

However in this wonderfully technological day and age it shouldn't be too difficult to produce an accurate digital thermometer, surely?

Will also see how closely the humidity readings agree.

Cheers

Dave R

Reply to
David WE Roberts
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How much different?

Reply to
Timothy Murphy

New pair 20.0 in 20.1 out Old pair (just reset outdoor sensor) 20.4 in 20.3 out Clock 19.7 (probably most reliable)

I must say this is the closest together I have seen the old ones.

So, range of 0.7C between the five of them. They are all in a row on the table, the outdoor sensors on a table mat to try and insulate them from the table. It has taken several hours for them to get roughly into agreement.

Humidity:

45% new 51% old

Cheers

Dave R

Reply to
David WE Roberts

In article , David WE Roberts scribeth thus

Not that bad a tolerance ...

Reply to
tony sayer

Confucius say "man with one watch always know right time; man with two watches never know right time!" (or in your case, temperature).

Reply to
Chris Hogg

So within the +/- least significant digit inherent error anyway.

Reply to
Dave Liquorice

You will be lucky if you find them within half a degree of each other plus or minus one unit of whatever the last digit is. The sensors are of the very cheapest kind. To do an accurate check you need to compare against certified thermometer.

Peter Crosland

Reply to
Peter Crosland

After my brother made comments about the inaccuracy of the temperature I went to a stall selling digital wall thermometers - there was a 10C difference between the lowest and highest reading.

-- Mark BR

Reply to
Mark BR

There are two good points about the simple dial with bimetallic coil: no decimals to worry about and can be easily adjusted. I've an old (~60 years) Hg in glass thermometer which I've checked a couple of times and use that for setting/checking other instruments.

As has been said, the sensors are cheap and prone to drift. At work we had very expensive instruments and controllers for testing for the MoD and Pentagon and even they would 2 or 3 points out after 6 months.

Reply to
PeterC

In message , David WE Roberts writes

Never ask more than one lawyer for a legal opinion either.

Why? Digital clocks aren't all that good.

Reply to
hugh

That would explain the alleged 0.7 degree rise in "global temperature"* in the last 100 years.

  • global temperature: an average of lots of wildly different redings from the Antarctic to the Sahara.
Reply to
Matty F

"reding" - a neologism for "red herring"?

Reply to
PeterC

They will all have different time constants, different susceptibility to air flow, etc, so it would be remarkable if they did read the same, unless they've all been in exactly the same temperature for some time.

It is quite difficult to take environmental temperatures, and the first hurdle is to understand why you want to know, and then the most representative way of taking a measurement that meets that need. This is something I went through a few iterations when designing and implementing my home automation and boiler controls. I came to the conclusion that I needed to place the roomstat about 4' high and about

3' out from the walls, but a pendant roomstat was too geeky even for me ;-)

From a human comfort and temperature perception point of view, the wet bulb temperature is much more meaningful than the dry bulb temperature most thermometers read out. This is because a human body is somewhat moist on the outside, so things like humidity and wind-chill have a significant impact, which they don't on a dry bulb.

Reply to
Andrew Gabriel

OK, I want to know the daily temperature at several thousand sites around the world, over a 150 year period, with due allowance made for cities and airports and carparks being built next to the thermometers. What is the effect of having a thermometer downwind from a 747 jumbo jet compared with a Sopwith Camel?

Reply to
Matty F

I have yet to see any satellite based measures show a significant rise.

Reply to
dennis

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Reply to
Roger Chapman

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not trustworthy. And I say that because I've looked at their code and their data management techniques, irrespective of any goings on implied by the contents of their leaked emails.

Reply to
Huge

snip

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Reply to
Roger Chapman

Reply to
dennis

In message , Matty F writes

A Sopwith Camel won't tell you the temperature

Reply to
hugh

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