temperature measurement

[mattt6065]

hi i am hoping to create a system which will take an analouge reading from a semitech GT thermistor and give me a real time temperature reading. i will be using the minilab 1008 to help me achieve this and was just wondering if anyone had any advice or had attempted a similar system before? the system is hopefully going to simulate a thermistat in the sense that when the temperature drops to a certain level the power to the heating system which will be represented simply by an LED will come on.

cheers

Matt

[SachaE]

Hi,

Since this is a thermistor, I'm assuming you're going to use the minilab with the D/A to provide excitation, and then read the voltage off across the thermistor with the A/D? (Using voltage excitation and resistor you can get an approach for the current excitation required, but it's not great and is the readon why we make specific signal conditioning interfaces that will do this with the excitation built in)

You don't say what programming language you're using with this either, so if we assume LabVIEW, then you'll need the drivers for it here : http://www.adeptscience.co.uk/products/dataacqu/hardware/product/miniLAB-1008/827/1/MINILAB%201008/p...  (link at the bottom of that page)

Also, watch for the input impedance of the minilab 1008 - I couldn't find it in the manual specifically, but depending on the impedance of your thermistor, you may end up with a potential divider happening, and not get the readings you expect. Your best bet is to actually talk to Adept to get specific details on wiring up a thermistor to your minilab 1008. (I did a search on their website for the word Thermistor = 0 results!) Try here for more information on the general setups :

http://zone.ni.com/devzone/cda/tut/p/id/4519 
http://zone.ni.com/devzone/cda/tut/p/id/4925 
http://zone.ni.com/devzone/cda/tut/p/id/3643 

Other than that, you simply need to read the values, maybe do some averaging for noise, and compare to a limit. You could include hysterisis if you wanted to make sure you're not just bouncing around the limit all the time, but that depends on how quick you need the system to react.

Hope that helps

Thanks

Sacha Emery
National Instruments (UK)