# Resistance Temperature Detector – Construction and Working Principle – Electronic Instrumentation

Do subscribe to Ekeeda channel and press bell icon to get updates about latest Engineering, HSC and IIT-JEE Mains and Advanced videos.Hello Friends,In this video we are going to study about resistance thermometers also known as RTD in this video we will study the principle of working construction and applications of RTD so let us start with our topic. Resistance thermometers they are also known as resistance temperature detectors or it’s short form is RTD these resistance thermometers they are the resistive transducers which measures the change in temperature by measuring the change in resistance okay so they are basically used for the measurement of temperature changes you if you want to measure the temperature we are having the thermometers for measuring the room temperature for body temperature so we are having the thermometers there so just like that if you want to measure the temperature changes in the metals what we do it is very difficult to measure it directly the variations in the temperature so indirectly we are measuring the temperature changes by measuring the change in the resistance because as the temperature changes the resistance octamer metals also changes okay now how the resistance is changing with respect to temperature we know that resistance is defined as the property of the material to oppose the flow of the current through it okay so in a metal or inner conductor if more amount of current is flowing to the conductor it means that its resistance is very less if less amount of current is flowing is it means that it is having a high value of resistance now this resistance it not only depends upon the current but it also depends upon the temperature now when this conductor it is heated up means that a thermal heat is provided to it thermal expansion is given then due to that thermal expansion the electrons because the current flow is all the flow of electrons so the flow of electrons it increases due to the thermal Heat so as the flow of electrons is increasing the flow of current also increasing and we can say that the resistance decreases so we can say that there is a relationship between the temperature and the resistance also like as we are increasing the temperature the resistance of the material it decreases because when temperature increases the flow of electrons increases the flow of current increases and the resist decreases so we are going to use your the relationship between the resistance and the temperature to measure the variations in the temperature okay so that is the principle behind the working of the resistance thermometers or resistance temperature detectors you so the principle behind it’s working is that the resistance of a conductor changes when the temperature is change now how the resistance varies with temperature there is a relationship between this there is an equation which defines this changes you so the variations in the resistance with the temperature here temperature it is in the standard units there is in kelvins and it can be represented by this following relationship which is R is equals to R naught 1 plus alpha 1 T plus alpha 2 v square plus 10 alpha n TN and this continues in this way means alpha 1 T plus alpha 2 T square plus alpha 3 T cube plus alpha 4 T raised to the power 4 plus alpha 5 T raised to the power 5 so in this way this equation continues now here this R is the resistance of the metal and are not it is the resistance at temperature T equals to 0 kelvins and alpha 1 alpha 2 alpha 3 till elf and these are the constants you so the resistance thermometers they uses this change in the resistance with the change in the temperature because the as the temperature is changing resistance is also changing so they are utilizing this principle that the change in resistance to determine the temperature changes or to measure the temperature variations you so that is the principle behind the working of the resistance thermometers that the change in resistance is used to measure the temperature now comes the construction of the resistance thermometer if we talk about its construction then the resistance thermometers they most probably they use the Platinum as its constructing material okay these are TDS they are made up of platinum okay now here we can use metals and semiconductors also metals they are having the property that they have a positive temperature coefficient positive temperature coefficient means that they are as the temperature increases their resistance also increases whereas in the semiconductors they are having the negative temperature coefficient that means as the temperature increases their resistance decreases so for the construction of the RT DS we are using the metals which are having the positive temperature coefficient whose resistance increases with the increase in the temperature you now for the construction of the RT DS most probably the Platinum is used so platinum is used because it is having the advantages that it is having you that doctor has the property that it can withstand high temperatures and maintain the excellent stability also and also it is a noble metal so it is very less susceptible to contamination so due to these properties platinum is used as the standard material for the construction of the arteries and also the metals can also be used because the metals they have the property that they have for their resistance it will give a positive change with the changes in the temperature okay so that is the main function of the RTD that with no temperature changes the resistance also change and they require a positive temperature coefficient so most of the metals are having positive temperature coefficient so they can be used for the construction of RTD but mostly in most of the cases platinum is used as the standard material for the construction of RTD now let us see some of the requirements which are expected from a conductor if it is used for the construction of our table because here I have said that Cottenham is used but also the conductors which are having positive temperature coefficient they can also be used for the construction of RTD so let us see the requirements of the material which can be used for the construction you so these are the requirements of the conductor material which is used in our TDs first is that it should have a positive temperature coefficient that is the first and the foremost requirement then the change in the resistance of the material per unit change in temperature it should be as large as possible so that if we are doing any my new changes in the temperature the change in the resistance should be so large that it can be measured easily so change in resistance per unit change in temperature should be as large as possible so that it can be measure correctly and quickly by the Artemis then the material should have a high value of resistivity so that minimum volume of material is used we know that the resistance it is it also depends upon the resistivity ro okay so if the resistivity of the material is very high then we have to use a very small amount of material for the construction of RTD okay but if resistivity is very less then a large volume or large mass of material has to be used so it is expected that this material it should have a high value of resistivity so that only a small amount of material can be used for the construction thought is that the resistance of the material it should have a continuous and stable relationship with the temperature okay the resistance should have a continuous linear relationship with the temperature then only we can measure the change in the resistance and we can measure the temperature variations okay so there should be a continuous and stable relationship with the temperature so these are the requirements which are expected from the material which is used for the construction of RTD now let us see the basic diagram of an art it is that what are the main parts of an RTD how it is composed you so this is the basic construction of the RTD how the Platinum resistance here the material which is used for the construction of RTD is the Platinum okay these are the connecting leads this these are the mounting leads lead support sheet and this is the element so here the element is the Platinum which is used for the RTD construction and when the temperature variations that when temperature is change the resistance of this element is going to change with the change in resistance we will be able to measure the changes in the temperature now as I said that mostly platinum is used for the construction of the RTD but other than platinum gold and silver they are also rarely used for the construction of RTD on account of their low resistivities because they needs a gold and silver they are having very low value of the resistivity so they can also be used sometimes also tungsten tungsten can also be used where tungsten has high resistivity but it has the advantage it has very high resistivity but it is reserved for the applications for the high-temperature applications because it is very brittle okay it can easily break and very difficult to work but it has the advantage that it can work further it can be used sometimes for the construction of our ticketing of the RTD other than this we are having copper copper is also used occasionally for the construction of RTD now other than these gold silver tungsten copper mostly we use platinum nickel and their alloys okay so sometimes gold silver tungsten copper they can be used depending upon the application for which RTD is used but most of the time the platinum nickel and the alloys of nickel are used for the construction of RTD platinum being the best choice in that because it is having a very single value for the resistance that is 100 ohm at zero degree Celsius with a resistance temperature coefficient of zero point zero zero three eight five four degree Celsius so that is the resistance temperature coefficient you can see that it is having a positive temperature coefficient so that is why platinum is the standard and the best choice for the construction of RTD now if we see the characteristics that how the temperature and the resistance of changing for these materials if we see the graph for it you so these are the resistance and temperature characteristics of the materials nickel copper and platinum you can see that for the Platinum they are getting an almost a linear relationship for nickel it is something non linear type and for copper it is also linear but after the temperature increases it becomes nonlinear okay so platinum is most probably use because it is having the linear relationship between the resistance and the temperature now if we see the characteristics for a small period of time okay like for small temperature range if we see the changes in the resistance we will see that we are having the linear relationship so for these graphs the characteristics graph we are having two type of approximations one is the linear approximation which we will consider for a short range of temperature and another is the quadratic approximation let’s see that what will be the relationship between the resistance and temperature in these two types of approximations in linear approximation we will have R theta equals 2 okay means linear approximation means that between the resistance and the temperature we are having a linear relationship we are minimizing the curve for we are considering the curve for a short range of temperature so in that case the equation which we have studied earlier which is R equals to R theta 1 plus alpha 1 T plus alpha 2 T squared so that equation will be reduced it will be it only this will be left okay now initially at in that equation we were having R naught which is the temperature at 0 degree Celsius now here we are considering the material which is earlier at temperature theta 1 and after that the temperature has been changed and it is Theta 2 okay so we want that when the temperature is change so what will be the effect on the resistance so your R theta is the approximate resistance at theta degree Celsius then our theta naught it is the resistance at theta naught degree Celsius and then theta it is the difference that is the change in the resistance that is theta minus theta naught so temperature changes are from theta 1 to theta 2 we are changing the temperature from theta 1 to theta 2 but we are considering on temperature which is in between in this range okay where we are getting a linear relationship between the resistance at the temperature so that linear relationship is between here first the temperature is theta naught and it has changed to theta okay so this difference in the change or the change in temperature we will calculate by using this formula by using this linear approximation now what about the quadratic approximation because here we are having linear relationship in quadratic we will have quadratic relationship between the resistance and temperature Swink quadratic approximation r theta so here you can see that we are having the linear part also and we are having the quadratic part also so this is the linear fractional change in the temperature and this is the quadratic fractional change in the temperature and all the other terms they are the same okay so in this way when we want to consider the what we want to find out the changes in the temperature for a short range we can use the linear approximation and for a greater range we can use the quadratic approximation also okay so in this video we studied about the resistance thermometers which are also known as the resistance temperature detectors or RTD we studied that what is the principle of working of RTD then we see the construction the Platinum which is most probably use for it its characteristics we have seen and we have seen that how the linear and the quadratic approximations are done on the curve for the resistance and temperature characteristics so in this we are so I hope that you have for this topic will be clear to you now and thank you

Thanks madam 😇😇😇

thanks mam

Thanks mam ❤️

The resistivity of a conductor increases with temperature. but u said just opposite

Thanks a lot man

Kowalsky analysis

Gud

At the 2end point of requirment of material.

You discussed that material should of high resistivity

So why u are taking gold for its construction🙋🙋

Excellent explained..!!

very well explain

thanks mam

😀😀………..it's clear..

Thankuu ma'am

Madam thank to make a great video lesson..I have requeste make video about vibration ( I mean industrial gas turbine) measurement , principal and calculations or equations about the rms values

Good explanation madam. If u had animations it is very will stores in the mind permanently

Mai RTD ka mtlb kya hi

Nice lecture mm I am a student mechanical engineering but I understood the work and principle of resistance thermometer easily…. Thanku👌👌👍

Hi

in RTDs, temperature and Resistance vary directly…

As temperature increases, so does resistance

Thank you mam….It's really helpful

Output of RTD and themocouple

Principle of O2 analyser??

Best video with great explanation …

Keep making this types of video

MAM aapke eq. Ke hissab se there is direct relationship between temperature and resistance. But in the beginning you told that there they are inversely proportional.

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RTD stand for Resistive Thermo Device not a detector? other word it's a thermistor for industrial measurement.

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All metals have a positive temperature coefficient of resistance, so that there resistance increases with increasing in temperature.

RESISTANCE OF METALS INCREASES WITH TEMPERATURE!!!!!!!!!

Mem this is your notes to see in you video so we can sme2sme put the exam,?????

Super mam

Please tell me PT-100 full meaning….

Nice teaching mam

Mam explain the strain gauge

tq for you video im watch the all video is nice and help in alla application of mesurement is using tq