Temperature sensors play an important role in the performance of electronic and electrical devices. There are various sensors used to measure the temperature and they include thermocouples, thermistors, and RTD (also referred to as a Resistance Thermometer or Resistance Temperature Detector).
Here, we are going to discuss the principle of thermocouple, which is used in several industrial applications, household applications, and domestic applications.
What is an RTD sensor?
An RTD sensor is an electric device used to monitor the temperature. Many of these detectors are known as wire wound.
The device is available as a length of fine wire made of platinum, copper, or nickel, wrapped around a glass or ceramic core. The metals (copper, platinum, and nickel) produce the most positive and accurate temperature coefficient.
Platinum is the most preferred type of metal or element because it:
• Offers high chemical and physical stability.
• Chemically inert
• Highly malleable and ductile, allowing it to easily turn into wires, films, and threads while retaining its dimensional stability.
RTD elements are housed in a probe to make them stronger and to protect them from the environment they are in. When compared to other devices, RTDs are among the most accurate in the industry.
In other words, RTDs are useful when the stability and accuracy of measurements are important.
Components of Resistance Thermometers
RTDs have six major components:
• Resistant element
• Wire configuration
• Tubing material
• Connection fitting
• Outer diameter
• Termination
The configuration of the components separates the various types of RTDs and their capabilities and accuracy.
Working principle of RTD sensors
A Resistance Thermometer works by using a basic principle that the resistance of a conductor changes because of a change in temperature.
A metal’s increase in temperature increases the flow of electricity. Similarly, when the temperature of an element used in the RTD increases, resistance also increases.
The detector changes constantly with respect to the applied temperature. This means that the temperature is predictable by resistance measurement. It’s this property that lets RTDs monitor temperatures more consistently and accurately.
The resistance value of RTDs can be determined by applying a constant current and then evaluating the voltage drops’s occurrence through the resistor.
Different applications of a Resistance Thermometer
Below are the applications of RTD sensors in various industries.
Medical electronics
Controlling temperatures is important, especially in cases of respiration devices, dialysis equipment, and infant incubation.
The Automotive industry
The devices are widely used in the automotive industry to measure water levels and air, engine and external temperatures.
Consumer products
For fire detectors and small appliance controls, like electric blankets and coffee makers.
HVAC
RTDs are used for fire detection and climate control.
Communications
Transmitters and amplifiers use great amounts of heat-producing electricity, which has been monitored and controlled.
Food processing
Each aspect of food production needs constant monitoring of temperatures. These sensors are usually used during shipping, storage, and manufacturing.
Heavy industry
Every electric and machinery motor has to be monitored for increases in temperatures that could greatly damage production. That is also true of generators, windings, microwave power, and ovens.
Chemical industry
The integrated systems and special chambers use these devices as controls and monitors to ensure safety and accuracy.
Pros and cons of RTDs
Advantages
• High accuracy
• Suitable for remote indication
• Easily replaced and installed
• It’s available in a wide range
• Good stability
• More linearity than thermocouple
• Long service life
• Offer repeatability
• Can be used when a high degree of standardization is desirable.
• Resistance to shock, vibrations, and temperatures.
Disadvantages
1. Lead error and self-heating when high accuracy is required.
2. Higher initial cost.
3. Bridge circuit is required with the power supply.
4. The detector needs a more complex measurement circuit.
5. Slower response time when compared to a thermocouple.
6. Low sensitivity.
7. Larger bulb size.
8. Needs three or four-wire operation.
RTD Sensors
Because of their stability and accuracy, RTD sensors are quickly replacing thermistors and thermocouples in industrial applications.
RTD sensors can give higher accuracy values and can be stable for years.
These electric devices are present in our everyday appliances, like cell phones, coffee machines, etc.
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