There are three main temperature sensor types: Thermocouples, Resistance Temperature Detectors (RTDs) and Thermistors. Temperature sensors are vital instruments used each day in a wide range of applications, including but not limited to:
Each application may require unique temperature sensing parameters such as what is being measured (air, mass, or liquid), where it is being measured (inside or outside), and the range of temperature being measured. Understanding the advantages and disadvantages of the temperature sensor types will help select the right tool for the right application.
The basic concept is that the resistance in metal reflects changes in temperature and that difference in resistance is what RTDs measure. An RTD is a resistor with well defined resistance vs. temperature properties. Platinum is the most common and accurate material used to develop RTDs.
The advantages of RTDs stem from their stability, accuracy, repeatability and fairly wide temperature range. The stability and accuracy derive from their almost linear response to temperature changes. RTDs are often preferred for precision applications because of their accuracy and repeatability.
Disadvantages include a higher thermal mass which causes them to respond more slowly to changes in temperature than thermocouples. They also require an excitation current to flow through the RTD. Other temperature sensors without this requirement are therefore better options for certain applications.
Configurations include two, three, and four wire options. The two-wire option is useful when lead length is short enough that resistance doesn’t significantly affect measurement accuracy. A three-wire adds an RTD probe that carries the excitation current. This provides a way to cancel wire resistance. Four-wire is the most accurate, as separate force and sense leads eliminate the effect of wire resistance.
Thermocouples are the workhorse temperature sensor type. They are used in many different applications. The advantages are numerous: thermocouples are self-powered, require no excitation, can operate over a wide temperature range, and have quick response times.
Thermocouples are made by joining two dissimilar metal wires together. This causes a Seebeck Effect. The Seebeck Effect is a phenomenon in which a temperature difference of two dissimilar conductors produces a voltage difference between the two substances. It is this voltage difference that can be measured and used to calculate the temperature.
There are several types of thermocouples that are made from a variety of different material, which allows for different temperature ranges and different sensitivities. The different types are differentiated by designated letters. The most commonly used is the K type.
Disadvantages of thermocouples include that their limited output voltage can make measuring temperature harder since it requires precise amplification, external noise issues over long wires, and cold junction compensation. Cold junction is where thermocouple wires meet copper traces of the signal circuitry. This creates another Seebeck Effect which needs to be compensated for in the measurements.
Thermistors, like RTDs, measure temperature changes caused by measurable resistance changes. Most Thermistors are made from polymer or ceramic material. In most cases, thermistors are cheaper but are also less accurate than RTDs. Most thermistors are available in two wire configurations.
The Negative Temperature Coefficient (NTC) thermistor is the most common thermistor type for temperature measurement. The NTC thermistor’s resistance decreases as the temperature increases, thus producing a non linear temperature resistance relationship. This requires a significant correction to interpret the data correctly.
These temperature sensor types, Thermocouples, RTDs and Thermistors, remain the common types of temperature sensors used today. Thermocouples are inexpensive, durable, and can measure a wide range of temperatures. RTDs offer a wide range of temperature measurements and provide accurate and repeatable measurements, but they are slower, require an excitation current, and require signal conditioning. Thermistors are durable and small, but they are less accurate than RTDs and require more data corrections to calculate temperature.
While there are other temperature sensor options available, these three options should offer a design solution for most applications.
It can be extremely beneficial to have a trustworthy medical thermometer at home. The ability to properly determine whether or not someone has a fever provides you with crucial information regarding the next stages in their treatment.
There are many different types of thermometers available, both contact and non-contact. Your family’s ages, as well as your own preferences, will help you to decide which one to purchase.
When someone is unwell, the last thing you want to do is rely on guesswork. Here’s a quick rundown of medical thermometers, including how to use them and what their readings imply.
Read on to learn about the advantages and disadvantages of different thermometers.
Digital thermometers are the most accurate and quickest form of thermometer. The readings are obtained from the underside of the tongue, the rectum, or the armpit. They are widely available in local pharmacies and can be utilised at home or in hospitals.
These thermometers take temperature readings using infrared technology. Electronic ear thermometers are less reliable because they might provide an erroneous reading if there is too much wax in the ear. Despite their high cost, they are far simpler to use on newborns and small children, as digital thermometers may be difficult to persuade youngsters to stay still for long enough.
These infrared thermometers are likewise put on the temporal artery and read heat. Digital thermometers are more accurate than forehead thermometers.
These plastic strip thermometers can identify if a patient has a fever, but they do not provide precise temperature measurements. They merely serve as a warning that something is awry. To use them, simply lay the strip on your brow.
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These pacifier thermometers are mostly used on newborns above the age of three months. They require the infant to remain motionless for a few minutes, which might be difficult. As a result, the temperature may be incorrect at times.
These mercury thermometers are for taking a temperature in an old-fashioned manner. Normally, you’d put it under your tongue and wait for the temperature to rise, when the mercury stops rising that is your temperature. Unfortunately, because of the potential of mercury poisoning, this method of taking a temperature is not recommended, and you should speak with a healthcare professional before discarding any you may have.
Both inner ear thermometer accuracy and forehead thermometer accuracy are excellent, and most devices can measure temperature to within ±0.2°C when used correctly. For extra peace of mind, search for thermometer types that have a CE Mark to meet the latest British Standards. CE Marking is the device manufacturer’s claim that their device meets the essential requirements of all relevant European Medical Device Directives. These Directives outline the safety and performance requirements for medical devices in the European Union (EU).
Because of basal body temperature, various thermometers can provide different readings, or the same thermometer might give different readings. Your basal body temperature varies depending on how long you’ve been awake, how much you’ve moved if you’ve stood up, and so on. This is why you should measure as soon as you wake up, before you nap, lie in bed for an extended period of time, or get out of bed.
Sensors in touch thermometers monitor their own temperature. Contact thermometers use the heat transfer process known as “conduction” to measure the temperature. They require direct contact with the measured object in order to bring the sensor body up to the temperature of the object.
In non-contact measurements, an infrared sensor is used to determine the temperature of an item by analysing the amount of infrared radiation.
When it comes to application advantages, the non-contact infrared thermometer outperforms the contact-type thermometer, because it is non-contact, this means that you can take measurements without disturbing whoever you are measuring.
Although the price of a non-contact thermometer is more than that of a contact thermometer, the non-contact thermometer saves personnel, material resources, and financial resources.
Adults can use any thermometer, here are our top thermometers based off your needs.
Best price: Digital Thermometer
Fastest readings: Inner Ear Thermometer
Non-contact: Ear and Forehead Thermometer
For children, you will want to go for either the Inner Ear Thermometer or the Ear and Forehead Thermometer. These are great options because they take fast accurate measurements which won’t disturb the child.
For babies, the Ear and Forehead Thermometer is the best option. If a baby is sleeping and you need to take their temperature without disturbing them, you can use the contactless infrared mode. The thermometer ambient temperature mode is also useful for checking how hot the baby’s milk is.
The thermometer is inserted beneath the tongue for this procedure. Adults and children aged 4 and above who are able to hold a thermometer in their mouth should utilise this approach.
The thermometer is carefully placed into the rectum for this procedure. This is most commonly done with new-borns, but it may also be done with children as young as three years old. Children older than 3 years can have their rectal temperatures taken, although it may be difficult to keep them as calm as they need to be.
For small infants or people who cannot properly take their temperature orally, the thermometer is inserted under the armpit. This approach isn’t as precise as oral or rectal, but it’s a good initial check. After that, you can do an oral or rectal reading.
This sort of thermometer uses infrared heat to determine the temperature inside the ear. Be careful to follow the device’s directions for appropriately positioning the tip for the best results. Ear thermometers might be quicker and simpler to use for older newborns and toddlers. They are not, however, suggested for babies under the age of three months. If your kid has excessive earwax or an earache, they should not be used.
Forehead thermometers are also used to measure temperature, although they are less dependable and typically more costly than digital thermometers. They are attached to the temporal artery of the forehead and measure the amount of infrared heat emitted by the head.
There are different thermometers for different situations. The best way to pick a thermometer is to assess your own situation. In many instances, you’ll have to think about the convenience of the person who is taking the temperature as well as the person getting their temperature taken.
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