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Member
SajjadSyed
Posts: 11
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Measuring resistance with 6008

Hi,

I am new to the DAQ field. I just want to know how I can measure a resistor with 6008. I am using VI Logger, DAQ 8.0 software. I have simply taken a 2K resistor and placed one end on AI2+ and AI2-. In VI Logger options, I am using "External" as Iex Source and Iex current of 1mA, which I think means that 6008 provides the exitation current. When I press test (run) button I see graph ranging from 1 to 6 ohms. Can you please tell me how I can measure resistance preferrable with no internal current source (I mean 6008 should take care of providing current source). If that is not possible how can I setup a constant current source. I will be taking resistance measurements on couple of channels of couple of different resistors later. Is there a better NI DAQ product that allows measuring of multiple resistances (resistances maybe less than 100 Ohms) without any extra hardware.

Please help.

Member RM2
Member
RM2
Posts: 49
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Re: Measuring resistance with 6008

I don't think the USB 6008 will provide an internal current source so you will need an external source. I dont know of other NI hardware that will do this but I am sure there is something.
Member
SajjadSyed
Posts: 11
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Re: Measuring resistance with 6008

Hi,

As I said previously I am just trying to measure a resistor on one of the analog channels. How do I setup a constant current source for it. I tried using a 9V battery with few Kohms resistors in series to give the load resistor a constant current of 1 mA. 6008 still doesn't see a resistance. Please let me know if you know any websites that describe this procedure.

Thanks.

Trusted Enthusiast
AnalogKid2DigitalMan
Posts: 3,184
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Re: Measuring resistance with 6008

Here is the datasheet and app notes for building a constant current source.

http://cache.national.com/ds/LM/LM134.pdf

Your approach to using a 9V battery and a series resistor is not a constant current source- your current will change as the battery's voltage drops and the current will also change with changing load resistance. But regardless, you should have been able to measure some voltage across your resistor under test. Are you sure your connections were correct?

1mA * 2Kohm will yield 2V

Let us know if you need further help, good luck!

~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~
Member
SajjadSyed
Posts: 11
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Re: Measuring resistance with 6008

Hi,

Yes I understand that my approach would not yield a consistent reading since I don't have a proper constant current source. But placing a resistor in series with 9V battery and then my load resistor should provide me atleast a reading. I need to know first that it is taking a measurement before I implement a current source. Can anyone tell me what analog channel(s) they use for resistance. The alternative I can think of is to use the 5V digital output, connect a variable resistor, load resistor and ground.

Trusted Enthusiast
AnalogKid2DigitalMan
Posts: 3,184
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Re: Measuring resistance with 6008

I am not familiar with VI Logger nor the 6008, but it should not matter what analog input channel you use to measure the voltage drop across the resistor under test. All I can suggest is make sure the anaolog input channel used is set to differential mode, if that is possible with your SW and HW.

The most direct off-the-shelf approach I can think of is to use one of NI's DMM products such as the NI 4060:

http://zone.ni.com/devzone/conceptd.nsf/webmain/E50CA0FE56C50A5486256E4B005EB49F?opendocument&node=1...

 

~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~
Knight of NI
Dennis_Knutson
Posts: 34,615
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Re: Measuring resistance with 6008

I would also suggest that you test everything in MAX first. I've never used the device or VI Logger but I'm assuming that you can find the device listed under Devices and Interfaces>NI-DAQmx Devices and then run the test panels.
Member
jmfox180
Posts: 6
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Re: Measuring resistance with 6008

hi well i guess i got what you want.. what you need to do its placing and external voltage source and then a known resistor value in series,  and then placing you LOAD resistor in series to that circuit , so with KVL (kirchhoff voltage law) you can measure the voltage in your LOAD.. that's known as an ohmmeter.. maybe that will help you xD