A thermometer is a device that is used to measure the temperature of a body. Common types of thermometers are Medical thermometers, Infrared thermometers, Mercury thermometers, thermocouple thermometers, laboratory thermometers, Bimetallic strip thermometers, Pyrometers, etc.
This Post Includes:
- Different kinds of thermometer
- Uses of thermometers
- Lots more
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Main Types of thermometer are given in the list below:
Clinical or Medical thermometers
A Medical thermometer is used to measure body temperature. Mostly thermometers made in the 20th century are mercury thermometers. They are sensitive and accurate, having a narrow place where the level of mercury rises very fast. A kink on the tube stops the mercury level from falling on its own.
These kinds of thermometers are used in the clinics by the doctors, so they are also called a doctor’s thermometers. It is used to measure human body temperature in the range of 35 °C to 42 °C. Medical thermometers are cleaned before and after each use, with alcohol.
It is used to measure the room temperature of hot solids and liquids in experiments. It measures temperature in the range of 5 °C to 110 °C and on higher temperatures.
Digital thermometers measure the temperature by means of an electronic circuit. The information they capture is sent to a microchip that processes it and displays it numerically on the digital screen. They are easy to use, fast, accurate and inexpensive. These are advanced thermometers used to measure the temperature of a body of a high level of accuracy.
How to use Digital or clinical thermometers?
In order for the body temperature to be measured correctly with the digital thermometer, the following steps must be followed:
- Turn on the thermometer and check if the number zero appears on the display;
- Place the tip of the thermometer under the armpit or carefully insert it into the anus, mainly to measure the temperature in children. In the case of the rectal route, you must lie on your back, inserting only the metallic part of the thermometer in the anus;
- Wait a few seconds until you hear the thermometer alarm;
- Remove the thermometer and check the temperature value on the screen;
- Clean the metallic tip with cotton or an alcohol moistened gauze.
Infrared ear thermometers
The temperature in the ear is also known as the tympanic membrane temperature or eardrum. This is one of the ways to take your body temperature using the inside of your ear. Children like this way of taking temperature because it is taken quickly. The normal ear temperature is 99.5 degrees F (37.5 degrees C) in adults. They should not be over-squeezed or used on ears with a lot of wax.
Infrared thermometers capture body heat in the form of infrared energy given off by a heat source. This type of thermometer is based on the fact that the laws that govern the radioactive emission of bodies allow the precise calculation of the temperature of the radiating object from its emission spectrum, without requiring direct contact with it.
How to uses an Infrared ear thermometer?
To use the thermometer in the ear, also known as a tympanic thermometer, you must:
- Place the tip of the thermometer inside the ear and point it towards the nose;
- Press the “power” button on the thermometer until you hear a signal;
- Read the temperature value, which appears instantly;
- Remove the thermometer from the ear and clean the tip with cotton or alcohol gauze.
The infrared ear thermometer is very fast and easy to read, so it requires you to regularly buy plastic protective caps, which makes using the thermometer more expensive.
Some Other Types of the thermometer on the basis of Technology
An ideal thermometer shall have an infinite temperature range. Since no thermometer is ideal, therefore we have a large number of thermometers.
It has linear expansion property and has a temperature range of -35°C to +500 °C(with compressed nitrogen). It works on the principle:
ΔL α ΔT
Where ΔT= Δl/lοα and α is the linear expansion coefficient.
How To use mercury thermometer?
The use of the mercury thermometer is contraindicated due to health risks, such as respiratory problems or skin damage, but there are also currently glass thermometers similar to the old mercury, called analog thermometers, which do not have mercury in their composition and can be used safely.
To measure the temperature with these devices, you must:
- Check the temperature of the thermometer before using it, observing if the liquid is close to the lowest temperature;
- Place the metallic tip of the thermometer under the armpit or in the anus, depending on where you intend to measure the temperature;
- Keep the arm that has the thermometer still next to the body;
- Wait 5 minutes and remove the thermometer from the armpit;
- Verify the temperature, observing the place where the liquid ends, which will be the value of the measured temperature.
This type of thermometer takes longer to measure the temperature than the others, and the reading is usually more difficult to do, especially for the elderly or the visually impaired.
Alcohol in glass thermometers
Made from sealed glass, it displays the temperature by the level at which mercury or alcohol reaches a graduated scale. These liquids dilate and contract due to changes in temperature. Generally, the measurement scale you use is Celsius, although it can also be expressed in degrees Fahrenheit. These thermometers currently contain colored alcohol due to the danger of contact with mercury.
Constant pressure gas thermometers
This class of thermometers can operate at both volume and constant pressure. Having a very precise measurement system, they are often used to adjust other thermometers.
In this thermometer, volume increases directly with the increase in temperature. It measures temperature in the range from o k 5oo k.
ΔV α ΔT
And γ=1/273 for ideal gases.
Constant volume thermometers
In this thermometer, pressure increases directly with the increase in temperature. It measures temperature in the range o k to 5oo k.
ΔP α ΔT
where ΔT=Δp/P triple point γ
=273 Δp/P triple point
Platinum resistance thermometers
These measure the temperature through a platinum wire that is attached to an electrical resistance that changes according to the temperature. Generally used to measure outside temperatures, it is very accurate, albeit slow.
In this thermometer resistance of the material in thermometer increases directly with an increase of temperature. It measures temperature in the range of 5oo k to 2300 k.
ΔR α ΔT
where ΔT=ΔR/Rα , α is a thermal coefficient of resistance.
These thermometers measure the temperature very quickly, they are generally used in laboratories. They measure the temperature through an electrical resistance that generates a voltage which varies according to the connection temperature.
This thermometer work on the principle:
emf ∈ = αT +β T²
In this scale is nonlinear. Temperature is either matched with a standard curve supplied by the manufacturer or a digital display is provided.α and β depend upon the materials used to form a thermocouple. where:
emf ∈=αT + βT²/2
It measures temperature in the range 500 k to 2300 k
These measures the temperature from the heat radiation emitted by the objects. These thermometers allow them to be used without having to touch objects, allowing them to be measured when they are moving or far away, as well as when their temperatures are very high.
This thermometer work on the principle of radiation. It measures temperature greater than 2000 k. It uses Stefan’s law:
Intensity E= σT4
They are suitable instruments for infants since they take the temperature of the same without causing any discomfort. Use the same as the standard digital thermometer for oral temperature.
Plastic strip thermometer
Certain plastic strips applied to the baby’s forehead can measure temperature changes at a given moment by giving a colorimetric scale that tells us, after putting it on a child’s forehead for a minute, whether a child has a fever or not. However, such measurement is not reliable but indicative.
Which Kind Of substance should Be Used In Glass Thermometers?
Some substances have the property that changes with temperature. Substances that show a change in temperature can be used as a thermometric material. For example, some substances expand on heating, some change their colors, some change their electric resistance, etc. Nearly all the substances expand on heating. Liquids also expand on heating and are suitable as thermometric materials. Common thermometers are generally made using some suitable liquid as thermometric material.
Which properties should present in thermometric liquid?
A thermometric liquid should have the following properties:
- It should be visible.
- It should have uniform thermal expansion.
- It should have a low freezing point.
- It should have a high boiling point.
- It should not wet glass.
- It should be a good conductor of heat.
- It should have small specific heat capacity.
Which liquids are used in a glass thermometer?
A liquid in glass thermometer has a bulb with a long capillary tube of uniform and fine bore. A suitable liquid is filled in the bulb. When the bulb contacts a hot object, the liquid in it expands and rises in the tube. The glass stem of a thermometer is thick and acts as a cylinder lens. This makes it easy to see the liquid level in the glass tube. Mostly Mercury and alcohol are used in glass thermometers.
Why mercury used in thermometers instead of water?
Mercury is used mostly in thermometers because of the following properties:
- It is visible.
- It has a low freezing point (-39 °C).
- It has a very high boiling point (357 °C).
- It expands linearly.
- It gives accurate measurements.
- It is a good conductor of heat.
- Fast response time.
- It has a wide range of temperatures.
Properties of Alcohols for thermometers
- It has a low freezing point (-112 °C).
- It has a boiling point of (78 °C).
- It is used to measure high temperatures.
- It is not a good conductor of heat.
- It has a bright color.
- It expands more than mercury.
- What are the different temperature scales?
- Difference between heat and temperature
- Types of transducers
- Heat transfer by conduction
- Heat transfer by convection examples
- Heat transfer by radiation
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