How Do Temperature Sensors Work

In the industrial automation, the Temperature Sensor is used to measure the temperature. The temperature sensor uses the converter to convert the temperature value to an electrical value. To read the temperature correctly & control the temperature in the industrial applications the temperature sensor is used more widely. In between the different types of sensors, we can make large peculiarities and the sensors will have the different properties like temperature range, contact-way, sensing element, and calibrating methods. The temperature sensor consists of a sensing element together in housings of plastics or metal. By using the conduction circuit the sensors will reflect the charge of environmental temperature.

What is a Temperature Sensor?

A simple temperature sensor is a device, to measure the temperature through an electrical signal it requires a thermocouple or RTD (Resistance Temperature Detectors). The thermocouple is prepared by two dissimilar metals which generate the electrical voltage indirectly proportional to change the temperature. The RTD is a variable resistor, it will change the electrical resistance indirectly proportional to changes in the temperature in a precise, and nearly linear manner.

Temperature Sensor Working

The measurement of the temperature sensor is about the hotness or coolness of an object. The working base of the sensors is the voltage that read across the diode. If the voltage increases, then the temperature rises and there is a voltage drop between the transistor terminals of base & emitter, they are recorded by the sensors. If the difference in voltage is amplified, the analogue signal is generated by the device and it is directly proportional to the temperature.

By using the temperature sensor, the temperature can be measured by four measurement scales and they are divided into different degree units. The metric Celsius scale is used by the measurement scale and they start from zero. The Fahrenheit temperature sensing uses the Rankin scales and these scales are absolute scales. The Rankin scale measures the absolute zero as the 492 degrees Rankin. The temperature sensor determines the absolute zero measurements as close to the minus 46 degrees Fahrenheit.

Different Types of Sensors

The different types of sensors include the following

Thermocouple Sensor

The thermocouple sensor measures the popular thermals, which are composed of the two different metal alloy wires. By combining the two different metals will generates the strong voltage which is the same capacity as a temperature. In general, the thermocouple gives the vast measurement ranges and they are worked by using the Seebeck effect. The Seebeck effect invested for changing the temperature in the electrical circuit. The sensor reads the temperature by taking the measurement of voltage output.

The performance of the thermocouple is good because it is up to 2,7500C. This sensor can also used for the short period of temperature up to 30000C and as low as –250°C. The benefits of these sensors, are they can measure the temperature by their own, near the junctions the thermocouples can’t measure the temperature, when it is compared with the resistance thermometer the thermocouple sensor reacts rapidly, the thermocouple are the electrical conductors, hence they cannot contact another source of electricity.

Thermistor Sensor

The thermistor sensor is a type of sensor. This type of sensors is used mostly in the human thermometers. If there is a change in the temperature, then the electrical current or resistance also changes. The thermistor is prepared by using the semiconductor materials with a resistivity which is especially sensitive to temperature. The resistance of a thermistor decreases with increasing temperature so that when the temperature changes, the resistance change is predictable.

The thermistor sensors are different from the resistance temperature detectors in that the first difference is the metal used in the RTD is pure metal and the second difference is the temperature response is two. The thermistor sensor is classified into two types and they depend on the sign of K. If the K is negative, then the resistance decreases with the increasing temperature and the device is called as the negative temperature coefficient. If the K is positive, then the resistance increases with the increase in the temperature and the device are called as the positive temperature coefficient.

 Resistance Temperature Detector

These are the temperature sensors with a resistor that changes the resistive value simultaneously with temperature changes. The RTDs are used in a wide temperature range from -500C to 5000C for thin film and for the wire wound variety the range is from the +2000C to 8500C. The thin layer of platinum on a substrate is present on the thin film RTD element. A new pattern is created which provide the electrical circuit and it is trimmed to give a specific resistance.

Lead wires are attached and to protect the film & connections the assembly is coated. In comparison, wire-wound elements are either coils of wire packaged in a ceramic or glass tube, or they can be wound around a glass or ceramic material. RTDs, which have higher accuracy and repeatability, are slowly replacing thermocouples in industrial applications below 600 °C.

Infrared Sensors

These sensors are used to measure the surface temperature and its range is from -70 to 10000C. They convert thermal energy sent from an object in a wavelength range of 0.7 to 20 um into an electrical signal that converts the signal for display in units of temperature after compensating for any ambient temperature.

Temperature Sensor IC

There are different types of temperature sensor ICs, which are available to simplify the broadest possible range of temperature monitoring challenges. There are two operations in the temperature range, the first operation is the temperature sensor can operate in normal condition with an IC temperature range of -550C to +1500VC. The second major difference is functionality.

The silicon temperature sensor is an integrated circuit, it consists of extensive signal processing circuitry contained in the same package as the sensors and for the temperature sensor IC the compensation circuit is not required. Some of these are analogue circuits with either voltage or current output. Others combine analogue-sensing circuits with voltage comparators to provide alert functions. Some other sensor ICs combine analogue sensing circuitry with digital input/output and control registers, making them an ideal solution for microprocessor-based systems.

Generally, the digital output sensors contain a temperature sensor, analogue to digital converter, two wired digital interfaces and registers for controlling the operations of integrated circuits. The temperature sensors are measured continuously and they can read at any time.

If preferred the host processor, it can instruct the sensor to monitor the temperature and produce the output pin high or low, if the temperature exceeds to program limits. Lower threshold temperature can also be programmed and the host can be notified when the temperature has dropped below this threshold. Hence, the digital output sensor can be used for reliable temperature monitoring in microprocessor-based systems.

A simple example of the temperature sensor is an LM35, it is a precision integrated circuit temperature sensor. The output voltage is linearly proportional to the Celsius temperature and the range of this sensor is -550C to +1200C.

The power supply of the LM35 temperature sensor requires 5.5V and it consists of three terminals of a material which perform the operation according to the temperature to vary resistance. When the voltage increases, then the temperature also rises. We can see this operation by using a diode.

Temperature sensors directly connected to microprocessor input, therefore it has capable of direct and reliable communication with microprocessors. The sensor unit can communicate effectively with low-cost processors without the need of A/D converters. The features of LM35 temperature sensor are explained below.

Features of LM35 Temperature Sensor

• Calibrated directly in ˚ Celsius (Centigrade)
• Rated for full l −55˚ to +150˚C range
• Suitable for remote applications
• Low cost due to wafer-level trimming
• Operates from 4 to 30 volts
• Low self-heating,
• ±1/4˚C of typical nonlinearity

Applications of temperatures Sensor

• The temperature sensors are used in the military/Defence
• It can be used in the home automation systems like air conditioners, refrigerators, microwave Owens
• It can also use in the industries like warehouses, mushroom cultivation.
• The temperature sensors are used to measure the temperature of the boilers in thermal power plants

This title gives the information on how the temperature sensor does work and their applications. I hope by reading this article you have gained some basic information about the working of temperature sensors. If you have any queries about this article or about the electrical & electronic projects based on temperature sensors, please feel free to comment in the below section. Here is the question for you, what are the functions of different types of temperature sensors.