Different types of temperature sensors.

Title:different types of temperature sensors
Why: Temperature sensor is the device which collect data from surrounding condition and give required out put in terms of temperature.

1) Thermocouples.

Thermocouple sensor is the most commonly used temprature sensor and it is abbreviated as TC. This sensor is extremely rugged, low-cost, self-powered and can be used for long distance. There are many types of temperature sensors that have a wide range of applications.

You can seen in fig.two different metals cromel and alumel connect to each other and out put gives us some Potential once input terminal is scene the heat.

A thermocouple is a voltage device that indicates temperature by measuring a change in the voltage. It consists of two different metals: opened and closed. These metals work on the principle of thermo-electric effect. When two dissimilar metals produce a voltage, then a thermal difference exists between the two metals. When the temperature goes up, the output voltage of the thermocouple also increases.

This thermocouple sensor is usually sealed inside a ceramic shield or a metal that protects it from different environments. Some common types of thermocouples include K, J, T, R, E, S, N, and B. The most common type of thermocouples is J, T and K type thermocouples, which are available in pre-made forms.

The most important property of the thermocouple is non-linearity – the output voltage of the thermocouple is not linear with respect to temperature. Thus, to convert an output voltage to a temperature, it requires mathematical linearization.

2) RTD (Resistance temperature detector)

RTD sensor give more accurate reading than other sensors, In this sensor the resistance is proportional to the temperature. This sensor is made from copper,nickel and platinum metals. It has a wide range of temperature measurement capabilities as it can be used to measure temperature in the range between -270oC to +850oC. RTD requires an external current source. However, the current produces heat in a resistive element causing an error in the temperature measurements. The error is calculated by this formula:

Formula = delta T=P*S

where, P=power produce                                                                                                                                   S=degree C/mill watt                                                                                                                               T= Temperature                                                                                    

There are different methods to measure temperature by using this RTD. They are two wired, three-wired and four-wired method. In a two-wired method, the current is forced through the RTD to measure the resulting voltage. but the main drawback is – the lead resistance is the part of the measurement which leads to erroneous measurement.

Three-wired method is similar to the two-wired method, but the third wire compensates for the lead resistance. In a four-wired method, the current is forced on one set of the wires and the voltage is sensed on the other set of wires. This four-wired method completely compensates for the lead resistance.

3)Semiconductor sensor

Semiconductor sensors are the devices that come in the form of ICs.or diode Popularly, these sensors are known as an IC( integrated controller ) temperature sensor. They are classified into different types: Current output temperature sensor, Voltage output temperature sensor, Resistance output silicon temperature sensor, Diode temperature sensors and Digital output temperature sensor. Present semiconductor temperature sensors offer high linearity and high accuracy over an operating range of about 55°C to +150°C. However, AD590 and LM35 temperature sensors are the most popular temperature sensors.

4) IR Sensors

Fig: IR sensor and IR sensor base temperature gun

IR (infra red) sensor is electronic instrument which is used to sense certain characteristics of its surroundings by either emitting or detecting IR radiation. These sensors are non-contacting sensors. For example, if you hold an IR sensor in front of your desk without establishing any contact, the sensor detects the temperature of the desk based on the merit of its radiation. These sensors are classified into two types such as thermal infrared sensors and quantum infrared sensors.

Thanks
Kiran Patil