About NTC

Hardware
1

Hello everybody,

Would you please tell me;

1.If I want to use a 4.7 k NTC in a circuit,if it means that the NTC’s
value in room temperature(ambient) is 4.7 k? And when a seller say that
this is a 4.7 k NTC;that means that,the NTC’s value in room temperature(ambient) is 4.7 k ?

2.For example; how to read a 4.7 k NTC;I mean that ,what are written on a 4.7 k NTC
that indicated it is a 4.7k NTC ?

3.And,if I make a 4.7 k NTC, hotter than the environment temperature,
for example,by a lighter,its resistance decreases due to its characteristic temp. curve
at its datasheet ?

                                                       Thanks,
2

  1. Yes. Generally thermistors are quoted at 25C. NTC means negative temperature coefficient, so as it gets hotter, the resistance goes down.

  2. I’ve never really seen any labelled NTCs…

  3. Yes. Google “tempbug instructable” for some example code for mapping a thermistor to a temperature.

3

FWIW. Early on, I had used the Steinhart-Hart equation to calculate temperatures. However, I found getting the coefficients for thermistors to be rather challenging most of the time. Most vendors didn’t even know what I was talking about. The results were “close”, but still had too much error and variability for our needs.

However, upon request, I was able to get vendors to provide a look-up table showing the relationship between temperature and resistance. I found most of the tables to be fairly consistent. So…I ended up going the brute force route and loaded the tables into arrays and now do a look up, interpolating between table values. This has proven to be very accurate, as determined by comparison with other quality temperature sensors.

Of final note, there are varying qualities in thermistors, just like anything else. We’ve found that getting the appropriate form factor for the need from vendors such as Kele or Dwyer Instruments gives us very accurate and consistent results. YMMV.