thermistor

[Isabella]

Hi All,

        I'm currently using a thermistor, 20Kohm to measure temperature. Below i attach how i connect from my DAQ to my waveform. but the values i get it 193 degree?!.

Did i did wrongly? Thank You.

Regards,

Isa

[RavensFan]

You have a value of 34 as the input to "voltage reference".  That seems kind of high.  I think it would be more on the order of a couple volts, or possibly 5 or 10V tops.

[Isabella]

Hi Ravens, the 'voltage reference' value = 34. because my thermistor will be measuring human temperature. Minimum 28 to 40 degree Celsius. Putting 34 as voltage reference is wrong? Thank You. Regards, Isa

[Isabella]

Hi Ravens,

                I did change the 'voltage refernence' to 5volts. Yet, my temperature on my waveform graph shows 113degree celsius.

[RavensFan]

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Isabella wrote:
Hi Ravens, the 'voltage reference' value = 34. because my thermistor will be measuring human temperature. Minimum 28 to 40 degree Celsius. Putting 34 as voltage reference is wrong? Thank You. Regards, Isa

---

34 is a temperature, the input is looking for a voltage value.  Go to Context Help for that VI, and read the detailed help.

It says "Voltage Reference (V_REF) is the reference you apply across a resistor of known value in series with your thermistor. This parameter defaults to 2.5 V, which is the reference voltage used on the SCXI terminal blocks. Use this value only when the Type of Excitation is set to Voltage Reference."

Also check to make sure you have it wired up properly.  You may want to put an indicator on the voltage coming out and see what the voltage is.  Try warming it up in your hand and cooling it off to see if the voltage varies.  Make sure you have the DAQ assistant set up correctly.  If you are still having problems, post your VI.

[Isabella]

Hi Ravens,

Voltage Reference (VREF) is the reference you apply across a resistor of known value in series with your thermistor means? Voltage across the resistor (positive probe) to ground (negative probe)? That's what u mean? If it is like tat, the value is 3 and the graph still shows 95degree celsius.

Thanks.

Regards,

Isa

[Isabella]

I put a indicator to see the value out from the DAQ. as temperature increases, resistance drops. is right. So it means, convert from voltage to temperature is wrong. right?

[Isabella]

Can i ask a question? R1 means wat? the value of the thermistor?

Thank You.

Regards,

Isa

[Isabella]

Hi,

    Can i ask a question? Voltage reference of what? The output? The thermistor? The IC chip i'm using?

    Merry Christmas to all of you.

Regards,

Isa

[smercurio_fc]

A thermistor is a resistor. It has no reference voltage. The resistance of the thermistor changes with temperature. Thus, if you measure the voltage across the thermistor you can determine the temperature. I would suggest that you do a bit of reading on thermistors first. You can start here.