Temperature Sensors
Temperature sensors are one of the most widely used sensors among the sensors around us. That is because of the thermal conditions and the effect of the temperature on human life and the surrounding worlds where very high temperatures or very cold temperatures can cause death for humans and animals.
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| Temperature Sensor |
The temperature change can even change the physical state of solids or the materials' properties as well as the performance of the equipment. That is why we need to monitor and control the temperature. In this article, we will discuss the definition of the temperature sensor when was started, its types, and its applications.
From the definition of sensors, we can define the temperature sensor as a device used to convert the temperature to an electrical signal. The temperature sensors could be found anywhere. At home in the fridge, irons, ovens, heaters, and air conditioners. It is also in the car to control the temperature of your engine to protect it from overtemperature and also to control the car cabinet temperature.
What is the history of temperature measurement?
Measuring the temperature started about 400 years BD by using the human hand to decide whether a person has a fever or not. That measurement developed through the invention of the thermoscope and the glass thermometer (which is used till now). The main difficulties of these old devices are the accuracy and the standardization of the scales (start and end points).
Modern techniques for temperature measurement were developed over time. In 1821 when the Seebeck effect was discovered by a German physicist called Seebeck. The Seebeck effect says that when 2 metals are connected at their ends, there will be a changing of volts across the far away terminals when the temperature changes.
This was the basis for building the most popular temperature sensor devices called thermocouples. There are two main types of sensing criteria as mentioned in the sensor article, digital and analog. We will discuss in detail the various examples and temperature measurement types.
What are the types of temperature sensors?
Thermostat or temperature switch:
One of the main types of digital temperature sensor is the temperature switch or thermostat which depends on the effect of the temperature on a material like copper by changing its physical properties like the length for example to work as a switch on and off to run or stop devices like heater in the iron, fans in your car, and the A/C in your car and home.
Normally this thermostat could be adjusted manually by increasing or decreasing the gap between the 2 contacts of sensors to allow more or less temperature to let the sensor change its state and as a result, the device will be run or stop. Normally the temperature switch or thermostat is equipped or designed to have a safe margin of temperature to protect the contacts from damage due to the fast and rapid change in temperature.
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| Temperature sensor - Thermostat |
Temperature gauge:
The idea and the operation of the temperature gauge are the same as the temperature switch but the difference is that the temperature gauge contains a pointer slides on a flat or round scale, o F or o C indicating the temperature. This sensor can’t be used in the temperature control circuits because it is not accurate at all and there is no electrical connection and also depends on the visual follow-up of the temperature.
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| Temperature Sensors - Temperature gauge |
Resistance Temperature Detectors RTDs,
Another type of temperature sensor is the RTD which are device whose resistivity changes according to temperature changes this is called the temperature coefficient (TC). These materials could be copper, platinum, and nickel. When the temperature changed the resistance changed based on the temperature coefficient.
The Positive Temperature Coefficient (PTC) means that the resistance will be increased by increasing temperature and the Negative Temperature Coefficient (NTC) means the temperature will be decreased by increasing temperature.
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| RTD temperature sensors |
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| temperature Sensors - PTC and NTC |
What are the PT100 and PT1000?
PT100 and PT1000 are temperature sensors that change their resistance with the change of temperature which is the same as the RTDs but, the difference is that there a resistance reference values which are (100 Ω and 1000 Ω at 0 o C).
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| Temperature Sensors - PT 100 |
How to check the RTDs and thermocouples?
Check the functionality of the resistance temperature sensor is done by using the digital multimeter and measuring the Ω of the device then trying to increase the temperature and record the measured value of the resistance. There are standard tables for each product of the resistance temperature sensors.
The measured values are compared with the values in this table to confirm the performance of the device. In the industrial sector, as the working and operation temperature is normally higher than other applications (sometimes exceeding 1500 o C) which need temperature control and monitoring like heavy industries like cement, glass, and steel industry, a special device is used such as thermocouples. The thermocouples are based on the seebeck effect explained at the start of this article.
The output of the thermocouples is mV changing with the changing in temperature. These thermocouples are described as special two metals that are connected together at the end forming the junction. When the junction is exposed to temperature a voltage difference in mV could be measured by a multimeter or voltmeter at the other terminals of the thermocouple.
The electrical signal that comes from the thermocouple could be used directly as a feedback signal in the control system to control or monitor temperature processes by comparing it with a predefined temperature set point.
Conclusion.
Because of the importance of temperature in our lives, we have to measure it first, monitor, and control that temperature. We discussed the history of temperature measurement which started about 400 BC and has been developed to reach the current situation.
There are many types of temperature measurements like temperature switches, temperature gauges, Resistance temperature detectors (RTDs), and Thermocouples. In the coming article, we will complete other temperature measurement techniques and applications
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