Temperature Readings

Thermometers are used to measure temperature. There are lots of different sorts of thermometers, each having a different use. This page describes just a few of them.

It is important to measure the temperature, as this makes a big difference to us in many ways. Farmers need to know when their seed will germinate, drivers need to know if there will be ice on the roads. Can you think of other reasons why we need to know how warm or cold it is?

When you have finished reading about this you may want to return to Collecting Data.

Units of Measurement All temperatures are recorded in degrees Celsius (ºC). This is the standard unit in Europe and most of the world. When reading the scale check first to see what each mark represents. On this scale, from the wet thermometer, each line represents one degree Celsius. You can then count on or back from the nearest number. This thermometer is reading just above 17ºC.
Data Checking All numbers should be reasonable. Some high numbers should be regarded as suspicious in the winter time. Would you expect 15ºC in winter? Very low numbers should also be looked at closely in summer. Would you expect 5ºC in summer? You should ask yourself if your readings are sensible. When the temperature drops below 0ºC water will freeze. This causes various types of frost. The frost on the rain gauge in the picture on the right was very pretty.
Maximum and minimum temperature Maximum temperature is the warmest (largest number) since the last reading. The Minimum temperature is the coldest (smallest number) since the last reading. The maximum temperature should never be smaller than the minimum temperature. The thermometer on the right is a special one for recording these temperatures.
Reading the maximum and minimum The 'Max/Min' thermometer can keep a record of the warmest and coldest temperatures when we are not there. When the temperature rises, the marker 'pin' in the right hand column is pushed upwards. It will stay there until you reset it. You read the bottom of the 'pin' (blue in this picture). When the temperature falls, the marker in the left hand column will be pushed upwards to show the minimum temperature. Read the 'pin' at the bottom point.
Maximum and Minimum Thermometers Can you see how the instrument is made up of one long, curved thermometer? This means that you must be very careful when reading the scales. Look to see if the number is a plus or minus. Check your reading when you have written it down! You need to reset this instrument, when you have recorded your data.
Wet and Dry Temperatures The current temperature is taken from the dry temperature reading. The purpose of the wet and dry temperatures is to allow you to work out the humidity of the air. See the Humidity page for more details.
Checking Wet and Dry Readings The wet temperature reading should not be bigger that the dry temperature. This is because when things are wet they are colder. On very dry sunny days these temperatures will be further apart. It is usual for the two temperatures to be fairly close together when it is raining.
Maintenance Make sure that the reservoir of water is topped up with clean distilled water. If it runs dry you will have two dry thermometers! The little bottle unscrews so that you can fill it.
Using ICT There are many cheap digital thermometers these days. The instrument in the image can measure the current, maximum and minimum temperatures in two locations. One reading is taken from an internal sensor, the other uses the probe on the end of the cable. See more information on the ICT page.