Please ADVICE.

[Vadim Gnatkovsky]

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.



[Attachment circuit.bmp, see below]


[See first answer for additional information]

[Vadim Gnatkovsky]

[Attachment(s) for question]

[Robert Denier]

"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.

-Robert