 Welcome to the session. Today's topic of the discussion is the thermistors and thermocouples, that is, a temperature transducer. And two of the examples of the temperature transducer is the thermistors and thermocouples. My name is Ajit Suryanshi. I'm working as assistant professor in the Valchen Institute of Technology in the Department of Electronics and Telecommunication. So what is the outcome of this today's session? So at the end of the session, a student will be able to select the appropriate transistors to measure the physical parameter that is here. In this case, it's the temperature. So before proceeding to the session, what should the knowledge you should have? You should have the knowledge of the material properties, especially the electrical properties. And you should also have the knowledge of the basic circuit analysis, electrical circuit analysis, that is. So temperature transducer. So what do you mean by the temperature transducer? Temperature transducer is a device which will convert input temperature into the other physical quantities, like pressure and others, pressure also. And especially it is the electrical quantities. So that's why it is called as an electrical transducer. So this is the electrical transducers. So converting the temperature into the equivalent electrical quantities. And electrical transducers, examples are the thermistors and thermocouples. So these two transducers, sensors, sense the temperature and converts into the equivalent electrical output. So that's why the thermistor and thermocouples is a type of the electrical transducers, thermistors. So what is meant by the thermistor? A thermistor name itself suggests the term which is derived from the term, and esters, that means it is a thermal and resistors. So thermistor is a special type of the resistors, which changes its resistance, which is a proportional to the input body temperature. So again, thermistor is of two types, NTC type and PTC type. NTC is a negative temperature coefficient, and PTC is a positive temperature coefficient. So what is meant by the negative temperature coefficient? That will be seen in the next slide. So NTC, for example, is manufactured from the metal oxides and semiconductors. So material used in the NTCs are the semiconductors and metal oxide. While in the PTC, material used is the conductor, because conductor exhibits the PTC type of the characteristics. That means the conductor's resistance increases with the increasing temperatures. So in the NTC, as the temperature increases, resistance decreases. That shows the negative properties. Now coming into the symbols of the thermistors. Symbol used for the thermistor is this is one which is used in the America, and this is used in the international. This is an international symbol for the thermistors. Now coming into the thermistor characteristics. So this is the characteristics of the resistance versus the temperature. So for the PTC, that is positive temperature coefficient. So you can see that as the temperature rises, a resistance rises. That is increase in temperature, increase in the resistance. That is a PTC, which shows the positive slope. If you find out the slope, this slope is a positive value. So this positive value, that positive value comes to this name. That is a PTC. That is positive temperature coefficient. And if the slope is a negative, that means the resistance increase in the resistance shows the decrease in the resistance. That is the resistance is inversely proportional to the temperature. In that case, it is a type of the NTC, that is negative temperature coefficient type of the thermistors. So here in this graph, you can see that is a negative slope. So in both the graph, that is for the PTC and NTC, for PTC, slope is a positive. And for the NTC, slope is a negative. Also one more point you have to observe in this graph is that both the graphs are linear. Again, one more interesting point you can note. If the slope is higher, higher is the sensitive thermistors. So once the slope is higher, you'll get the higher sensitive thermistors. So it is also depend upon the slope. Next. So again, these two types of the characteristics that is PTC, this is the ideal one. So that shows the linear relation between the resistance and temperature. But that is not happening in the practice. In the practice, most of the cases you see the linear relationship. In the linear relationship, or exponential relationship. So in the exponential relationship, the resistance is the exponentially related to the temperature. You can see in this equation, Rt is equal to R0 of beta 1 upon t minus 1 upon t0, where Rt is the resistance of that thermistor, that particular temperature. And R0 is the resistance of the temperature at 0 degree Celsius. So and this beta value is depend upon what material used in the thermistors. If it is anti-seed type of the thermistors, then the material used will be the semiconductors or metal oxides. Again, this is an example of anti-seed thermistors, negative temperature coefficient of the. Can you measure the temperature by using anti-seed or PTC thermistors for a wide range if the relation between these two are not linear? So this is a non-linear relation. This is a linear relation. This is a non-linear relation. So can you measure the temperature for anti-seed and PTC types of the thermistor for a wide range, temperature range if the relation between these two are non-linear? That means this kind of the relation. Or non-linear relation means it exhibits the linear characteristics or it exhibits the exponential or any other type of the relation between these two parameters. And after that temperature, it becomes a constant. So if the answer is S, then write down the explanation. If the answer is no, write down the explanation. So you may pause this video, think about it, write on the piece of the paper. Answer is S. You can use it for the wide temperature range, provided that it should not get a saturated. Now coming into the construction of the thermistors. So these are the different construction. So again, the material used in the thermistors are the metal oxides. For example, a copper oxide, magnesium oxide. So these metals are used. And different form of the structures are formed by using these materials. It is the forming of the bead type of the structure. It is forming also the probe type of the structure. It is forming the disk. And it is also forming the rod type of the structure by using these materials. Now coming into the applications, there are different applications for the NTC. It is used for the very low temperature applications. It is used in the digital thermometers. While the PTC is used as over current protection circuits, because current is which is related to the temperature. As temperature increases, that means a current also increases. Because the rise in the current in the conductor that leads to the increase in the temperature in the conductor. So that can be sensed with the thermistors. And it can be used for the over current protection circuits. So this is about the thermistors. Coming into the thermocouple, one of the temperature transducer. Thermocouple is another type of the sensor which can be used to measure the temperature at the particular specific point. And it will provide the electromotivors. That is a voltage at the output, which is proportional to the temperatures. So basically the thermocouple has two different types of conductors which are joined at one point, which is called as a junction. Or that junction is also called as a hot junction. So again, these two wires are of different types. This may be the copper, this may be the ion. So provided that these two wires should be of different type or different materials. Now thermocouple construction. Again, these two are the different types of the wires. And this is what it's called as a hot junction. And these are the metal oxide. And these are the protection circuits. So it is made of the alloy of the constantin and ion. So again, it is made of the ion and the constantin. Now coming to the working of the thermocouple, it is based on the effect that is C-beck effect. So one junction is a cold and other junction is a hot. In that case, you may expect the voltage at that end. So provided that these two metals should be of different materials. So that is called as a C-beck effect. And this voltage will be proportional to the temperatures. So these are the applications. There are different applications in the chemical plant also to monitor the temperature of the chemical. It is used. It is also used in the cryogenic, that is, low temperature application. These are the applications of the thermocouple. These are the references for the temperature transducers. Thank you.