Making a thermometer can be very fun and will help you to have practical experience of basic temperature measuring technics. For the kids, it could be a long time memory to start playing around with science by making simple thermometers at home just for the fun of it.
BASIC CONCEPTS AND WORKING PRINCIPLES OF THERMOMETER
Thermometer is a temperature measuring instrument that indicates the hotness and coldness of any object including the surrounding. It stands as the basic signal for most technology for the purpose of controlling heat as well as cold.
The concepts of thermometers include temperature interaction with the surrounding and consequent response to the effects made by the interaction. It aims to show the level of changes as well as the duration of each change. It started early as the science itself, temperature measurement started when the science itself started hence it could be referred to be part of the basic science, hence the making of thermometer is as old as history.
In terms of working principles, all the thermometers work on the principle of thermal expansion and contraction. The impact of the temperature of materials leading to expansion and contraction of the materials.
TYPES OF THERMOMETERS
There are varieties of thermometers and their classification is based on the material used in the making, the temperature reading scale, and their working principle.
The list of varieties of thermometers includes:
Liquid-based thermometers are the ones working basically on liquid expansion principles. They are loaded with liquid that expands and contracts according to the temperature of its surrounding. Depending on the actual design, some have liquid-filled tubes at the interior center while some have it at the exterior to form part of its casing.
The part of a liquid-based thermometer referred to as a bulb carries a larger volume of the liquid and helps its expansion and contraction to the maximum and minimum levels. The bulb is usually located below the tube and becomes the part of the thermometer usually exposed to the source of the temperature to be measured.
A good example of a liquid-based thermometer is the hospital thermometer. The thermometer is used in measuring human body temperature. Doing its application, the bulb will be inserted into the armpit of the patient and the body temperature will cause the liquid in the bulb to either expand or contract in volume. The rise or drop in the initial gauge in the thermometer calibrated tube is the measure of the human body temperature being measured.
The above working principle of the hospital thermometer is applicable to all liquid-based thermometers including those being used in the school laboratories.
There are special liquids used in making liquid-based thermometers. Though every liquid has its own thermal expansion, not all will be suitable for thermometer application. For instance, water evaporates at 100 degrees Celsius, the alcohol evaporates at a lower temperature to that of water, and while some liquid does not evaporate easily a good is mercury.
In terms of thermal expansion ranges, ethanol and mercury appear to have wider expansion ranges than other liquids. For that reason, they are among the most preferred liquids used in the making of liquid-based thermometers.
Based on the above considerations, mercury is usually applied in liquid-based thermometers targeted at measuring high temperatures below the boiling point of the thermometer while ethanol is used in the making of liquid-based thermometers that will be measuring low temperatures below zero degrees Celsius and below the boiling point of the ethanol.
In terms of advantages, the liquid-based thermometers are easier to use, they are cheaper, simpler to construct, and small to carry in the pocket. The liquid-based thermometers are also faster in responding to stimuli. They indicate temperature changes very fast and provide needed accuracy in temperature measurements.
In terms of disadvantages, the liquid-based thermometers are breakable and fragile thus easily get damaged. The thermometers can experience liquid leakage due to defects after a long time. The thermometers only measure medium hot temperatures and extremely low temperatures below their freezing and boiling points.
Metal-based thermometers are temperature measuring devices that are working basically on metal expansion. The expansion of two dissimilar metals creates the temperature changes that are indicated on the scale. Though it still works on the principle of thermal expansion, the difference here is that the expansion takes place in metals rather than liquids. The metal receives heat or cold temperature and responds according to the temperature received. For hot temperatures, the metal will be expanding while for the cold temperatures the metal will be contrasting.
The expansion and contraction of the metals used in the making of the metal-based thermometers are basically reciprocal of the temperature received from the surrounding. The effective ones make use of two dissimilar metals with a wide range of thermal expansion differences such that while one expands the other remains static, the difference created is indicated on the measuring scale and that is the temperature being received from the surrounding.
The metal-based thermometer has a lot of advantages over the liquid-based thermometers, it is more durable in service, and it can measure very high temperatures up to 1000 degrees Celsius or more and low to temperatures up to -200 degrees Celsius. The wide temperature range readings made it a suitable choice for industrial applications and areas with wider temperature variations.
However, the metal-based thermometers have their own disadvantages which include; high cost of purchase, bulky size more than the liquid-based thermometers, lower response to temperature changes than the liquid-based thermometers, more complexity to build than the liquid-based thermometers.
Metals combinations such as zinc and iron, tungsten and nickel, etc. are among the various combinations used in the making of metal-based thermometers.
RADIATION THERMOMETERS (PYROMETERS)
The radiation thermometer is a modern temperature measuring device that works basically on radiation received from the surrounding or targeted source. In other words, the radiation thermometers known as pyrometers use optical scanning to indicate the level of radiation received from the object to be measured. Since radiation increases with temperature, the measure of the radiation is an indication of the temperature of the body being targeted.
The working principle is quite different from the liquid-based thermometers and metal-based thermometers. Instead of direct contact with the body being measured, the thermometer points its optical scanner on the object to be measured and without any direct contact with the body, it could analyze its radiation and converts it to a temperature reading.
It usually comes with a digital display and has an inbuilt power source to power its optical scanner and overall operation. It is an electronic device that applies modern physics laws and optical/radiation laws to provide a temperature reading.
The Pyrometers have higher advantages than liquid-based thermometers and metal-based thermometers. They measure a very wide range of temperatures and are therefore suitable in every application that needs a thermometer, they can take an accurate reading of temperatures from any object without the object in other words, and the temperatures are taken by simply pointing the pyrometer on the object to be measured. The contactless ability of the thermometer has made it the best option in all applications. This thermometer has gradually displaced other types of thermometers in the modern applications of thermometers.
Despite its unique advantages, the radiation thermometer has its own disadvantages which include; bulky size, technical experience on how to use it, the need to provide cells for its operations, possible interference of radiation from the neighboring objects while measuring tiny objects, and difficulty of building one or maintaining damaged ones, etc.
Pyrometers are available in industrial electronics shops in various sizes and brands.
WHY DO YOU NEED A THERMOMETER
From the discussions made above, you can notice that virtually everyone needs a thermometer either for personal use or for group use. Depending on the intended application, someone can choose to acquire one of the above-mentioned thermometers.
You can use a personal thermometer to:
Measure temperature of your room and interiors
COST OF THERMOMETER
The cost of a thermometer depends on the type of thermometer. The cheapest ones are the liquid-based thermometers followed by the metal-based thermometers and then the pyrometers. The factor that will determine the price differences in each type are temperature measuring range and the quality of material used in their making.
HOW TO MAKE A SIMPLE THERMOMETER
This is basically what this post intends to show you. I will be showing you how to make a simple thermometer at home. Based on simplicity and cost we will be discussing the making of the liquid-based thermometer.
The following are the things you need to provide to set up a simple thermometer at home:
- A Small narrow plastic tube or a narrow glass tube or the tube of your finished writing pen.
- Get a small metal or glass bulb such as an injection drug bottle, a broken end of a small glass tube, or any small metal bulb with a tiny opening.
- Mercury or ethanol liquid
- Sealing rubber tape or plastic solder
Steps and Procedures Involved
- Fill up the metal or plastic bulb with the liquid
- Insert the small plastic or glass tube into the bulb from the opening at the top, do not allow the tube to rest on the bottom of the bulb but it should go deep enough to get the liquid in the bulb to start showing on the tube.
- Use the sealing tape to seal the openings between the tube and the bulb at its top
- At this stage, your thermometer is ready for testing. However, you can use a bigger glass tube or plastic to cover the smaller tube and seal the bigger tube to the top of the bulb.
- Calibrate your thermometer using an ice block and a pot of boiling water. Insert the bulb into a pot of hot water and heat the water until it starts to boil. Take the reading at the point the water starts to boil by making the level of the liquid indicated in the narrow tube that level is 100 degrees Celsius. Use a reflective plate to pack cubes of ice blocks together and insert the bulb of the thermometer into the ice blocks and take the reading at the point the ice blocks start melting to liquid that is your zero degrees Celsius point. Now measure the distance between the zero (0) degrees point to the 100 degrees point using a ruler. Divide the distance into 10 points, each point will represent 10 degrees Celsius. Use a piece of waterproofed paper to write the calibration and wrap it around the outer tube or the intersection of the outer tube leaving space to be seeing the level of liquid in the internal small tube.