Resistance thermometers are used to measure the temperature of a sample. They come in two different forms: contact and non-contact. Contact thermometers come in three forms: infrared (or infrared thermometer), thermocouple, and thermopile.
According to Process Parameters (https://www.processparameters.co.uk/platinum-resistance-thermometers-pt100-pt1000/) the type which is best for you depends on your needs, budget, and how often you’ll be using the device.
We’ll discuss the differences between the contact and non-contact thermometers, including their pros and cons, and explain which one is best for your needs.
What Material Make Resistive Thermometer?
The resistance thermometer is a device made of a sensitive element from a pure metal such as Nickle, copper or Platinum. Temperature is directly proportional to metal resistance. Mostly, platinum is used in platinum resistance thermometers.
The two reasons behind the choice of platinum resistance thermometer are that platinum can withstand high-temperature range and has high stability.
Silver and Gold are not suitable materials for making RTD since they are low in sensitivity. Tungsten can be used, but it is brittle. Copper can be used when making RTD elements since it is cheaper and low in resistivity.
Nickel wires are used only in a limited temperature range.
What is the Working Principle of a Resistance Thermometer?
Resistance temperature detectors work when there is a temperature change; hence they change the resistance. They are made from a platinum wire wrapped around a glass or ceramic core or on a ceramic base.
All resistance thermometers need to comply with the international standard (industrial rts).
Resistance temperature detectors work on the correlation between temperature and metals. Therefore, resistance thermometer application is wide. The resistance of electric flow in metal will increase if the metal’s temperature increases.
Also, the resistance thermometer temperature is directly proportional to the electric resistance. Therefore, an increase in the pt 100 temperature will increase electrical resistance.
Resistance temperature detectors are specified based on their resistance at 0 degrees Celsius. This means that at 0 degrees Celsius, the resistance thermometer should be reading 100 ohms.
Resistance Thermometer vs Thermocouple
Resistance thermometers and thermocouples are two of the most used utilised temperature sensor in the market and industry. Therefore, the two has several data loggers, converter repeaters, regulators, signal transmitters and data acquisition modules.
Resistance thermometer
It is one of the most popular temperature sensors, also known as the pt 100 sensor or RTD. It works by taking advantage of metal resistance change as temperature functions. It contains temperature coefficient elements that are modest value and positive.
Platinum resistance thermometers offer higher performance based on linearity, accuracy, measurement field and duration over time.
It comes in two categories: wire-wound and thin-film.
A wire wound is made of a thin platinum wire wrapped around the glass or ceramic core. Thin-film sensors consist of a vacuum, and a layer of platinum of a few millimetres squire on the ceramic substrate.
A resistance thermometer is a contact thermometer. Therefore, the protecting material around it should be well selected to suit the installation condition and the purpose. Some RDT types are fairly corrosive resistant. They can measure a large temperature range but less than a thermocouple.
Disadvantage of contact resistance thermometer
• Expensive
• It cannot be used in a detailed measurement
• Low sensitivity degree
• Resistance influence from the contact
• Their sensitivity to acceleration and impact
Thermocouple
They are among the most used temperature measuring device since they can measure a wide temperature range and are easy to replace. The main disadvantage is accuracy. There are non-linier instrument.
When choosing the right thermocouple, ensure the measuring device is compatible with the connector. Also, you should consider the manufacturing characteristics, isolation, and temperature to be measured.
The above factor affects the measurement reliability and accuracy.
Contact and non-contact thermometer
Contact thermometer must touch the body being measured while non-contact can measure temperature without touching the body being measured.
Advantage of contact thermometer
• They are appropriate for children, new-borns and infants
• They can record temperature from different parts of the body faster
Disadvantage of contact thermometer
• Can cause discomfort
• The oral temperature will require a minimum of 15 minutes after a drink or food.
• It can be difficult for people who breathe with their mouths.
Advantage Non-contact thermometer
• Are appropriate to all age
• Easy and fast to record temperature
Disadvantage of Non-contact thermometer
• There are expensive
• They can be less accurate on some conditions
Resistance Thermometer Final Thoughts
Both contact and non-contact thermometer have their advantages and downside. Therefore, when selecting the type of thermometer to use, ensure you pick the one that suits your needs and the body to be measured.
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