Weather Banter - View Single Post

JPG · June 8th 06, 10:56 PM posted to uk.sci.weather

On 8 Jun 2006 13:41:24 -0700, wrote:

Les Hemmings wrote:
My car
doesn't have a thermometer and I was thinking of adding one of those digital
ones with a probe on the end of a wire. Anyone tried this with any success?

I have bought them from Maplin (cost around a tenner).

First thing is to calibrate (well sort of calibration) by finding the
error when the probe is in melting ice - it should of course be zero
C (distilled or previously boiled water). You then have a rough guide
as to the error.

The temperature readings cannot be expected to have absolute accuracy,
but do permit comparisons. I have determined the local hot (and cold)
spots for example.

I have mounted the probe beneath the door mirror in the airflow.
Airflow is essential - readings are meaningless when the car is
parked. Occasionally, when the sun is shining on the probe, it will
over read even when moving.

Don't be confused about cooling or heating as a result of the
airflow. At normal motoring speeds, the effect can be ignored. At
aircraft speeds (pilots apply corrections) it does become a factor from
about 150 mph upwards.

Is that due to compression ahead of the probe or friction, I wonder
Jack?

A very senior Met Office scientist I knew used to ask potential
candidates for stream 1 (as it then was) posts a fairly simple
question:

What happens to the recorded temperature of a thermometer in a wind
tunnel when the wind speed is increased?

Reflecting the current poor performance in science many candidates,
some of them with top physics degrees, used to answer, somewhat
intutitively but totally incorrectly, that the temperature would fall.

Martin

Jack