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Software to convert NTC resistance into temperature

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Software to convert NTC resistance into temperature

Postby jmaril » Tue Feb 24, 2004 9:26 pm

I assume that the electrical resistance of a NTC thermistor follow the relation:

R/Ro = Exp[K(1/T - 1/To)]
where:
Ro is the resistance @ To
R the rsesistance @ T
T and To are 'absolute' temperature (°C + 273.15)
K is the thermal coefficient of the NTC thermistor

The simplest electronic scheme would be a power supply, the NTC thermistor and one fixed resistance Rm all in 'serie' and measuring the voltage around Rm:

Voutput = Rm/(Rm+R) * Vo

Who could help me ?
I would like to use this with the Voltage input of DrDAQ
Thanks
jmaril
 

Postby markspencer » Thu Feb 26, 2004 9:27 am

Hi,

From what you have suggested to meaure the resistance of the therminster is fine, so long as you realise the Rm's resistance is also liable to change with temperature swings, as the varying voltage, thus current is passed through it. It migh be very small, changes and it will depend on the accuracy that you are trying to achieve.

I am unable to comment on the formula you have stated for the temperature conversion, but I did find something similar at this website. Hope it helps:

http://www.maxim-ic.com/appnotes.cfm/appnote_number/817

Best regards
Regards,

Mark Spencer
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Software to convert NTC resistance into temperature

Postby jmaril » Thu Mar 11, 2004 6:02 pm

Hi,

Thanks about the link to MAXIM ICs
I will read the paper as soon as possible and make comments if necessary.
Now, I need to record at least 8 temperatures plus other data; so I would need some 12-input ADC and logger...

jmaril
jmaril
 

Postby markspencer » Fri Mar 12, 2004 9:00 am

Hi,

If you are needing 8 channels of temperature, I would recommend that you look at our purpose built TC-08 8 channel thermocouple converter.

Picolog can use multiple instruments, at the same time, so one unit for temerature and another for the other data readings.

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Postby jmaril » Wed Mar 17, 2004 6:45 pm

Tnanks about saying that
Picolog can use multiple instruments, at the same time

I didn't even tried to open several PicoLog windows while I dit it for PicoPlayer !
jmaril
 

Postby markspencer » Thu Mar 18, 2004 10:31 am

Hi,

There are two ways of using multiple instruments, either in the same instance of Picolog or by running different instances of Picololg.

To use the first method tick the 'Multiple converter' box on the 'Recording window'. Then add the converters and set the channels (parameters).

The second method is slightly more complex.

Open Picolog in the usual way. This opens the first instance, then to open the second:

Start | Run

enter in the 'Open' box .... c:\pico\plw32.exe second.plw

c:\pico is the default path to the installation, if you have not used this then enter the correct path name. This will then start another instance, one this has worked, you can create a shortcut. On your desktop, right click the mouse:

New | Shortcut

enter the same text in to the command line, again adjusting the path name if necessary:
c:\pico\plw32.exe second.plw

Click next and enter a name for the shortcut.

Click Finish

The above steps can be repeated many times to create different instances of Picolog, all that needs to be done is change the name of the .plw file.

Best regards,
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Mark Spencer
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