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Hello. I have DAQCard-1200 and LabVIEW 5.0.1f. I should measure resistance in range 100 - 1000 kilohms. Can I do it? Please advice me. Can I use +5V from pin 49 in my DAQCard for this task?
Is circuit (see attachment) will be work? Ohm's law.
"Vadim Gnatkovsky" wrote in message news:38934d0a@newsgroups.ni.com... > Hello. > I have DAQCard-1200 and LabVIEW 5.0.1f. > I should measure resistance in range 100 - 1000 kilohms. > Can I do it? Please advice me. Can I use +5V from pin 49 in my DAQCard for > this task? > > Is circuit (see attachment) will be work? > Ohm's law. > > Thank you. > Vadim Gnatkovsky. > > >
The circuit you have is wrong. Use something of the form.
+5V--Ra--Rb--GND
Connect ACH0 between Ra and Rb. Call its measurement V0
Ra=known resistor Rb=unknown resistor.
I=5Volt/(Ra+Rb)
Rb=Vach0/I
or
Rb = (V0 * (Ra+Rb))/ 5volt
Rb = ((V0 *Ra) / 5volt) + ((V0*Rb) /5volt)
(1-V0/5volt) * Rb =((V0*Ra)/5volt)
Rb=(V0*Ra)/(5volt*(1-V0/5volt))
For this to work you should check that
Imax=5volt/Ra
is less than the maximum current that the +5volt supply can source.