If you look around your sign , you will come up lots of dissimilar devices whose goal in life is to eitherdetect or measure out changes in temperature :
In this clause , we will look at the different thermometer technologies used today and understand how they influence . You will also get to build up your own thermometer!
Bulb Thermometers
Thebulb thermometeris the uncouth glass thermometer you probably grew up with . The thermometer contain some case of fluid , generally mercury .
Bulb thermometers rely on the round-eyed principle thata liquid changes its volume relative to its temperature . liquidness take up less outer space when they are cold and more space when they are warm ( this same master works for petrol and is the basis of the spicy air balloon – for more information , seeHow Hot Air Balloons Work ) .
You probably work with liquid every twenty-four hour period , but may not notice that things like water , Milk River and preparation oil all take up more or less infinite as their temperatures change . In these cases , the change in volume is fairly small . All bulb thermometers employ a fairlylarge bulband anarrow tubeto accentuate the alteration in loudness . you may see this for yourself by making your own bulb thermometer from scratch . Here is what you ’ll postulate :
To make your thermometer :
What you have created is a childlike incandescent lamp thermometer . And it works pretty well . If you wanted to you couldcalibrateit , and it would tell you the temperature pretty accurately . This picky thermometer has a few problems , however :
Sealingmercuryin a small meth thermometer solves these problem . The minor sizing of the bulb means that the bulb reaches the temperature of what it is value very quickly , and the tube in such a thermometer is micro - fine . Mercury also avoids the freezing and stewing problems associate with water .
How do youcalibratethe thermometer ? Two common scale are used :
As you may see , the temperature scale we commonly use are completely arbitrary ! You could derive up with your own scale of measurement if you wanted to . The freezing and stewing point of water are nice because they are easily reproduce , but there is nothing to say that you could n’t use another scale .
Bimetallic Strip Thermometers
Bulb thermometers are good for measuring temperature accurately , but they are harder to utilize when the end is to control the temperature . Thebimetallic stripthermometer , because it is made of metallic element , is good at controlling thing .
The principle behind a bimetallic strip thermometer bank on the fact thatdifferent alloy expand at dissimilar rates as they warm up . By bonding two dissimilar metals together , you’re able to make a simple electric controller that can withstand fairly high temperatures . This sort of controller is often notice in oven . Here is the general layout :
Two metals make up the bimetallic strip ( hence the name ) . In this diagram , the dark-green metal would be chosen to spread out quicker than the disconsolate metal if the twist were being used in an oven . In arefrigerator , you would expend the opposite setup , so that as the temperature rises the blue alloy expands faster than the unripened metal . This causes the strip tobendupward , making impinging so that current can flow . By adjusting the size of it of the gap between the strip and the contact , you control the temperature .
You will often find longsighted bimetal stripscoiledinto spirals . This is the typical layout of a backyard telephone dial thermometer . By gyrate a very farseeing comic strip it becomes much more sensitive to small temperature changes . In a furnace thermoregulator , the same technique is used and amercury switchis attached to the volute . The electric switch deform the furnace on and off .
Electronic Thermometers
It is now common to measure temperature with electronics . The most uncouth sensor is athermoresistor(or thermistor ) .
This gadget changes itsresistancewith change in temperature . A estimator or other circuit quantify the resistance and converts it to a temperature , either to display it or to make decisions about deform something on or off . If you would like to build your own electronic thermometer , check outHow Microcontrollers Work .
For more information on thermometer and related matter , check out the liaison on the next Sir Frederick Handley Page !
