Reading a thermistor from a USB-1608FS

[ILJS]

I would like to read a thermistor from a Meaurement Computing USB-1608FS (I actually want to read 8 or 16 of these, but I have already started to set this up). I am going to use a very simple thermistor from digikey ($0.36 per thermistor), but I am very unsure on how this is done.

I am using a function that scans channels of a certain board (I think that it is set such that my board is board zero), and then I ask it to scan throught 16 channels and put these values into an array. I then transform these values to engineering units and do some conversion formulas to get out the temperature -- or at least this is all a part of my plan.

What is the best recommended way to take 16 voltages of a board such that I have? What is the best way to set up a simple thermistor?

Thank you,

ILJS

[Jennifer O]

Hello ILJS,

Thermistors are basically resistors whose values (resistances) change with temperature.  Generally a precise excitation current is applied to the thermistor and the voltage is read back. From the measured voltage and known current the resistance can be calculated (Ohm's Law)  and temperature is determined.  Measuring Temperature with an RTD or Thermistor is a tutorial which should help to get you started.

I recommend contacting Measurement Computing for information on using the Measurement Computing USB-1608FS.

Regards,

Jennifer O.
Applications Engineer
National Instruments

[Murrs]

Hey ILJS,

I'm trying something very similar. Were you able to succede? Please let me know what you ended up doing.

Cheers,

Murrs

[mallorim]

Hello Murrs,

This is a rather old post so I am not sure if you will receive a reply from ILJS. Can I ask what hardware you are working with and what the exact application involves? I can then try and provide some recommendations.

Regards,

 Mallori M.

[Murrs]

I am relatively new to Labview and working with DACs, btu basically I have a resistor that will change between ~500 kOhm to ~10 MOhm. I need to reliably measure this R value. For hardware I have a Laptop (Windows XP), a USB 1608FS (Measurement technologies). Now the 1608FS will allow me to measure voltage, but not current. I have no reliable current source. I guess I could put a 1 MOhm resistor in series with the variable resistance, and measure the voltage across it with a known voltage across both resistive components and back calculate the voltage drop/current.

A major limitation though is current. I'd like to stay on the uA current level, but reduce the amount of noise. I know I can do some of the noise cancelation using Labview, but I'd like a clean a signal as possible.

Any advice you may have would be appreciated.

Thanks 🙂

Murrs 

[mallorim]

Hello Murrs,

I am unfamiliar with your third party acquisition device, but if it is only capable of measuring voltage, then the Developer Zone article Resistance Measurement- Indircet Method will be very helpful. It sounds like you are on the right track though.

With regards to noise removal, much of this can be done is software post processing as you mentioned. Some suggestions for noise prevention on front end include following the suggestions in the Developer Zone article Field Wiring and Noise Considerations for Analog Signals for proper grounding of the measurement and using wires that are shielded twister pairs for all the connections. With regrads to the signal processing to remove noise, the following documents might be helpful:

Noise Reduction

Reducing the Effects of Noise in a Data Acquisition System by Averaging

Hope this information helps,

Mallori M