How to read an NTC 10K thermistor with Picolog TC-08

Post any questions you may have about our current range of USB data loggers
Post Reply
amalavart
Newbie
Posts: 0
Joined: Tue Nov 05, 2019 5:36 pm

How to read an NTC 10K thermistor with Picolog TC-08

Post by amalavart » Tue Nov 05, 2019 5:48 pm

Hi,
I have seen this question once before on this forum but I have not really understood the answer so I would like to ask it again: is it possible to read an NTC 10K thermistor (part number B57551G1103F005) somehow with my Pigolog recorder TC-08 please?

I would like to read 4 thermistors in parallel and I am aiming for 1 reading per second at 0.1K resolution or better and I don't care much about the absolute accuracy. What is the easiest setup to do this please? I am mostly interested in getting an output table of time versus temperature so could re-scale the data afterwards in a spreadsheeet if needed. As an add-on, would I also be able to measure some standard K-type thermocouples with the four leftover inputs?

I am a mechanical engineer so if you could help me with a short explanation and a nice little graph showing how to connect things together, that would be fantastic please!

Thank you in advance for your help.

Ali

AndrewA
PICO STAFF
PICO STAFF
Posts: 245
Joined: Tue Oct 21, 2014 3:07 pm

Re: How to read an NTC 10K thermistor with Picolog TC-08

Post by AndrewA » Wed Nov 06, 2019 3:40 pm

Hi,

The standard method using a resistor divider is shown here using some of our other loggers.
https://www.picotech.com/support/topic19621.html
The main issue would be supplying a low voltage reference voltage to power the resistor divider, to work with the TC-08.
For a single supply voltage you need around 100mV which is not easy to generate, and would need to be as temperature stable as possible.
The TC-08 does not offer any dc output to power circuits or devices.
So you would have provide this to reference voltage your resistor divider with the NTC.

On the plus side your output from the NTC could be upto 0-78mV which is half the ADC range of the logger. ((2^16) /2) 32768 steps noise free.

I am not sure if you would get to 0.1K = 0.15C accuracy over all.
I depends on what temperature range you want to setup the NTC to measure. The full range of your NTC is -55C to +300. (from the table in the datasheet)
this gives delta 355C / 32768 steps = 0.0108C per ADC step, if you can use the full half positive range of the logger.
You would need to calculate the sum of errors at for the reference voltage, NTC Tolerance, resistor divider and logger.

On the software side using Picolog 6 you can use a lookup table or Steinhart-Hart equation to calculate the temperature.

Vishay has guide for Selecting NTC Thermistors- https://www.vishay.com/docs/33001/seltherm.pdf
But there also a lot other information relating using NTCs.
Also-
https://www.tdk-electronics.tdk.com/download/531116/19643b7ea798d7c4670141a88cd993f9/pdf-general-technical-information.pdf
Regards Andrew
Technical Specialist

Post Reply