What is Thermistor: Definition and 57 Discussions

A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word is a combination of thermal and resistor. Thermistors are widely used as inrush current limiters, temperature sensors (negative temperature coefficient or NTC type typically), self-resetting overcurrent protectors, and self-regulating heating elements (positive temperature coefficient or PTC type typically). An operational temperature range of a thermistor is dependent on the probe type and is typically in between −100 °C (173 K) and 300 °C (573 K).

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  1. R

    Possible to change a thermistor resistance curve?

    Currently when set to 1C, the fridge cools to and maintains 4-5C(As a conversion when set to 34f it cools and maintains approx. 40f. ), all functions like fan/defrost are working correctly. Potentially the main board has an issue but all other zones are working correctly so I would prefer to not...
  2. PhysicsTest

    Engineering Interfacing of NTC thermistor with microcontroller

    I am trying to understand a circuit where the NTC thermistor is interfaced with micro controller, but i am not able to understand the voltage output at 25DegC. According to the ST website the output of the circuit is 1.4V but as per my calculations it is 1.05V, i am not sure why. Please help...
  3. T

    NTC thermistor heat dissapation calculation with graphs

    I couldn't solve this problem. Any tips or help would be appreciated. If I am violating against any rules please comment, as this is my second post :-).
  4. K

    Is a 1 Ohm reading normal for a cold 12 volt thermistor?

    I've just joined the Forum and not sure if I'm in the right section (or possibly Forum even). The 12 volt thermistor in question is extremely common and is fitted to many makes of car and motorbike. They do fail from time to time however and so I set about determining if one is functioning...
  5. thegreengineer

    Electrical How can I waterproof an electrical component?

    Good evening, it's been a while since my last thread here in PF. I will go straight to the point: I want to measure temperature using an NTC3950 thermistor. My circuit diagram is as follows: It's basically a voltage divider. By varying the temperature acting upon the thermistor the output...
  6. E

    Does anyone know the bandwidth of a thermistor?

    I had an experiment I was working on where I needed to know the temperature of a circuit element down to 10uS time resolution. I had a thermistor handy, so I thought I would attach it to the element, force a constant current into it, and look at the voltage change on a scope. This would...
  7. adamaero

    System turns on alarm once temp. dips below 10.5°C

    Homework Statement Homework Equations (Above given. I think it's a hint.) The Attempt at a Solution How is delta T = 0.25?? Where is the 10kΩ coming from? We were given a solution for this homework, since it's not collected. It just seems out of order.
  8. L

    Try to determine the resistance of an NTC thermistor

    I am currently using a Wheatstone bridge to determine the resistance of a NTC thermistor(Futher information about thermistor: http://www.apogeeweb.net/article/38.html) and feed the difference to the setpoint (analog potentiometer) as the error signal to a PID controller, giving me a way to...
  9. F

    Can the Voltage Drop PTC Thermistor Homework Statement be Solved?

    Homework Statement Homework Equations I am not sure exactly what this question is asking for, especially in regards to the voltage drop. How would the graph of voltage drop vs Rmax-Rmin be any different to what is already provided? The Attempt at a Solution
  10. T

    NTC6K523 Thermistor Replacement | Exact Values for 0-100°C Temperature Range

    Hi guys, I need replacement for this thermistor , values in table : https://drive.google.com/file/d/0Bxv5z9DWZ7ZwajNUbTRtVkN0TWs/view?usp=sharing If there is any exactly replacement, its enought same values from table for ( 0 to 100 degrees celsius) Thank You Matus
  11. M

    The resistance of a thermistor

    Homework Statement The resistance of thermistor over a limit range of temperature is given by equation R=c/(T-203). Where c is constant ant T is absolute temperature. What would be temperature on centigrade scale of thermistor at absolute temperature T=300k? Homework Equations i)R=c/(T-203)...
  12. K

    Electricity -- Effect of heating a thermistor in this circuit

    Homework Statement The thermistor is heated so that its resistance decreases. State and explain the effect this has on the voltmeter reading in the following positions. A–C Homework Equations V=IR[/B] The Attempt at a Solution :[/B] I will say that the voltage will increase because if the...
  13. F

    Thermodynamics and thermometers (Thermistor)

    1. The problem statement, all variables, and given/known data Q1 Resistance at 0 degrees Celsius = 3840 ohms Resistance at 100 degrees Celsius = 190 ohms Resistance at ? degrees Celsius = 2300 ohms a. Calculate the temperature of the water according to calibrated thermistor assuming the...
  14. J

    Uses of a silicon semiconductor at high temperatures

    We conducted an experiment in which we found the variation in the resistance of a fairly pure silicon sample between temperatures of about 400K to 600K, and we found a value for the energy gap of silicon of our sample. We were comparing the resistance variation with the model...
  15. moenste

    NTC thermistor in a circuit

    Homework Statement A student is provided with a 2 V cell, a lamp, a switch and a thermistor with a negative temperature coefficient of resistance. The lamp, which is in series with the cell as in Figure 1, lights immediately the switch is turned on. Explain why (a) when the thermistor is...
  16. S

    What Are Good Alternatives for PTC Thermistors with Sharp Resistance Changes?

    Hi all, I'm new here so I thought I'd give this a shot. I'm developing a relatively high power power electronic system and I want a hardware shutdown for over-temperature without going back and revving my PCB too extensively. One effective way to accomplish this is with a PTC with a sharp...
  17. B

    Resistance of thermistor in hot water as it cools

    Homework Statement A student investigates how the resistance of a thermistor varies with temperature. Student immerses a thermistor into a 50 degrees Celsius beaker of water and measures the resistance on an ohmmeter as the water cools. Student adds ice to achieve lower temperatures. Q1. The...
  18. B

    Thermistor cooled in water and effect of temperature

    Homework Statement A student investigates how the resistance of a thermistor varies with temperature using an ohmmeter. To measure the temperature of the thermistor she immerses it in a water bath. At the start of the experiment she fills the beaker with the water at 50°C. She takes...
  19. ilovescience85

    Interface NTC thermistor with microprocessor

    Homework Statement A microcontroller for temperature limit control has a 0 V to 5 V power supply. An NTC temperature sensor provides an input voltage to a ・} 5 V comparator op-amp. Depending upon whether the temperature is below or above the set limit, the output from the opamp comparator will...
  20. A

    Potential Divider: R(R+r)*E=V - Wrong Ans Explained

    Homework Statement http://puu.sh/dzujr/dcf208c4a5.png Homework Equations Potential divider concept--> R(R+r)*E=V The Attempt at a Solution When there is low light, resistence of LDR increase to produce light. So, voltage across LDr increases and voltage across thermistor decrease-->lower...
  21. T

    Thermistor Selection for TP4056: NTC Resistance Guide

    I'm thinking about buying a tp4056 and I'm wondering what thermistor I should buy. I looked at the data sheet and it said a new NTC but that was it. So I went online to find one and I noticed they have resistance and I don't know which one to get. Could someone help me figure this out?
  22. B

    Thermistor Problem: Finding Material and Equation

    Ok so I am trying to figure out what type of material a thermistor should be, and am using the equation ΔR=kΔT (R being the resistivity, k being the temperature coefficient of resistivity, with which I want to find and match it up with a material, and T being the temperature). I have the change...
  23. M

    Thermistor temperature sensitivity

    Homework Statement . (a) It was pointed out in Section 15.3 that the temperature sensitivity of conductivity in semiconductors make them superior to traditional thermocouples for certain high-precision temperature measurements. Such devices are referred to as thermistors. As a simple example...
  24. C

    Test Your Knowledge: Thermistor MCQ with D as the Correct Answer

    The books answer is D. No clue why though Thank you for you effort
  25. Femme_physics

    Control system - Thermistor, thermocouple, PT100

    I'm 95% sure I got it all correct, but I'd appeciate another set of eyes Homework Statement 1) What's a thermistor? What is its principle of action? 2) What's a thermocouple, and what is its principle of action? 3) How does temperature transducer act based on the bimetal principle...
  26. W

    Warming a laser diode using a thermistor

    I use a green laser pointer at night to do astronomy related work. I got a cheap $5 green laser pointer off of ebay, and when it's a warm summer night, the device works fine. However, the second it touches the cold, it fizzles out and gives me almost zero output. My idea was to use a...
  27. Femme_physics

    Yet another Wheatstone bridge with thermistor

    Homework Statement So I got a thermistor here and am told that in the range 0-80 celsius the thermistor's resistance is given by Rt = R0 - kT ...whereas R0 = 100 ohms which is the thermistor resistance at 0 celsius. k = 0.5 kohms/celsius. T is of course temperature. The op-amps are ideal and...
  28. Femme_physics

    Thermistor in Wheatstone's bridge

    I'm told to presume that R1=R2=R3 http://img716.imageshack.us/img716/7610/thermistor.jpg And I have a chart for the value of the thermistor based on the temperature. At 20 degrees the thermistor is 2814 ohms My question is since they told me that R1=R2=R3, does it necessarily mean that...
  29. T

    How to connect thermistor without a PIC

    Hey hello, I am new in electrical system design. I almost know nothing. I need your help. And I have to control a DC motor's speed. My DC motor is 6V and I am not going to use a PIC. Is it possible or not I thought it was possible but as I said I know nothing. I thought of buying a NTC...
  30. D

    Transistor acting as a switch in closed circuit (with a thermistor)

    Homework Statement Ok so I have been given a diagram which if it worked should be attached. I am having a fair bit of trouble understanding it. Now I am aware that there is both electrical and conventional currents but I am confused as to whether this is electrical or conventional. I have been...
  31. S

    Thermistor and Op-Amp Circuit Design

    Homework Statement A thermistor T is included in the circuit shown. Calculate the resistance of resistor R such that the output of the op-amp will change polarity at 6oC if at that temperature the thermistor has resistance 3 kΩ Homework Equations The Attempt at a Solution The...
  32. N

    Calibrate thermistor and collect data

    Hi Guys, I am working on a project and am not that electrically savvy so I was hoping if someone could let me know how I'm doing. I want to use analog temperature probes (10K thermistors) and record data to a input module, which will convert it to Modbus (a communication protocol) that I...
  33. P

    Calculate thermistor coefficents

    I'm using Visual Basic to graph data from a NTC thermistor and temperature sensor (via a DAC card). I want to calculate the thermistor coefficients R0 and B according to the equation (R0 should have subscript 0): R = R0.e^B/T...
  34. E

    Build a Thermistor: Step-by-Step Guide, Cheap Options

    I want to build a thermistor or temperature detector that would shut down the system if over heated. Could someone post the step by step process to do so. Cheapest one possible.
  35. H

    Steinhart Temperature vs. Actual Temperature from thermistor resistance

    I'm pretty confused on what the difference between what the temperature reading is from a thermistor vs. the Steinhart Temperature. Basically I know that the "Steinhart–Hart equation" is given as: However, the http://www.vishay.com/docs/29049/23816403.pdf" for the thermistor I am...
  36. W

    Buying a Thermistor for Heat Detector Project - Factors to Consider

    what factors i had to take into account by buying a thermistor for my project of heat detector? my project circuit is attached.
  37. S

    Finding resistance for NTC Thermistor @ 25C

    1. Homework Statement Find the resistance of an NTC thermistor @ 25C, given a B value of 3950 K, operating temperature of -55C - +125C, with resistance ranging 5-100 kohm. Basically I framed this as a question from the thermistor's respective datasheet (found at...
  38. E

    Thermistor Temperature- Ohms Law?

    Thermistor Temperature- Ohms Law?? Hi All! I am trying to convert a current of 795mA to a temperature in degrees celcius but I don't understand how to do it. I realize that Ohms law of V= A/ R is involved somehow but that's the extent of my knowledge. PLEASE HELP! I have also been...
  39. R

    Measuring Fluid level using a thermistor.

    Hey I've been writting reports on strain gauge and thermistor. Ive completed my strain gauge report and now i am working on my thermistor report...ive been doing some research on them and i was wondering if this is the correct information i have gathered. so I have been asked from my...
  40. E

    Thermistor vs Thermocouple

    Hallo I am going to make a micro-calorimeter and in this micro-calorimeter I need a very sensitive temperature sensor. I think I am going to use a thermistor or a thermopile. But which one to choose? With which temperature sensor do I get the highest sensitivity? And with which temperature...
  41. xunxine

    What is the correct circuit symbol for a thermistor?

    I came across a few variations of the circuit symbol for thermistor. I've attached one below. I'm more used to the version with horizontal line at bottom left and rise to the top right. Is there any fixed or correct version? Or are all equally correct? i.e. the orientation of the line doesn't...
  42. MacLaddy

    Thermistor on Motor Control Board

    I work for a company which performs repairs on exercise equipment. One of my biggest problems is a constant failure of a Thermistor resistor on a certain brand treadmills motor control board. I am guessing poor design, but I am hoping somebody can clear up exactly what a thermistor resistor is...
  43. L

    Measuring resistance of thermistor in potential dividers

    Hi there, first off I hope this is ok to post here. Quite a simple question. I have done an experiment simply to work out the resistance of a thermistor at different temperatures, I did a prelim with a simple circuit of just ohm meter + thermistor. Then I did the main one with a potential...
  44. R

    Help designing a thermistor circuit

    I want to design a thermistor circuit to be sampled by a microcontroller using an 8 bit ADC, with a voltage reference of 2.55V, I know the following T (ºC) R(ohms) 25 2815 40 1200 I am going to use a potential divider then use a linear approximation to measure the...
  45. K

    Calculating temperature using NTC thermistor

    Hello, i was doing a practical experiment using NTC thermistor. I recorded the resistance at different voltages (1v, 2v, 3v, etc) and to find the temperature i need to use the temperature coefficient formula "The Steinhart-Hart equation": R(T) =...
  46. G

    Thermistor relationship, linearizing (really easy)

    hello, I'm doing coursework on using a thermistor as a temperature sensor. For my preliminary readings I had to choose between 3 different thermistors. Is it true that, for example, a 22k thermistor has a resistance of 22kohms at 25 degrees? (my tutor told me this) likewise, a 15k thermistor...
  47. P

    Thermistor + Simulink: Temperature Control in xPC Target Toolbox

    Hi Everybody, I'm doing a small project for my studies, I'm developing the xPC Target toolbox of Matlab. well the point is that i need to do a temperature control, I'm using a thermistor as temperature sensor and i need to insert a block into simulink of the thermistor to start to make the...
  48. B

    Can a Cylindrical Thermistor be Used to Build a Fuel Flow Meter?

    I need Cylindrical Thermistor to build a fuel flow meter. Need suggestions... Thanks
  49. E

    NTC Rod Thermistor Resistance Temp Coefficient @ 293K

    what is the temperature coefficient of resistance of a th3 ntc rod thermistor @ 293K?
  50. S

    Obtain the resistance of a ntc thermistor

    Please Help! HI. Im really struggling to work out how to obtain the resistance of a ntc thermistor from just having the temperature. I've been given the characteristic temp. of 3900K, labelled B for some reason. the only equation i can find to use is R = A.e to the power of B/T. I think this...
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