Measuring current and voltage at the same time using PCI 6036E and displaying

[sk515]

Ive set up a simple circuit to try and see if I can measure the current and voltage, to get an I-V plot.  Im having trouble measuring at the same time. 

At first I tried running two DAQmx tasks but i would get error 50103 "something about resources have been reserved"  Through searching the forums, I have found that running two analog inputs even on difference channels is not allowed. 


I tried the solution posted here:
http://forums.ni.com/ni/board/message?board.id=170&message.id=121899&query.id=15793#M121899
and adding a waveform output to something simlar to this and the error messages disappears, however, it won't display the waveform. 

I also "freezes" at a number when i turn on the power supply connecting the circuit.  I am measuring the current in series with the circuit, and voltage across a resistor.  Could that be causing the problem?

Thanks for any help!

[Dr._Imad]

search the LV examples for the simplest example of reading voltage.  you can use channels 0 and 1 using the syntax

ai0:1

The voltage that you can measure should have a range from -10 to +10.

also, you cannot measure the current directly by connecting it to a channel.  connect the output to a resistor (say 250 ohms).  one end of the resistor should be connected to ground and the other to the daq channel (say channel 1)

[Dennis_Knutson]

A DAQ board only measures voltage. So, to measure current, take the voltage reading across the resistor and divide by the resistance (Ohm's Law). A single channel is all that is required. Make sure that the resistance gives you a voltage that's within the voltage range of the DAQ board. If the current that you were trying to measure directly exceeded the max for the DAQ channel, you may also have damaged the DAQ board.

[sk515]

ive measured current using the DAQmx, where I created a task to measure current, that works fine, ive confirmed it with a multimeter.  my problem is reading the current and voltage simultaneously. and plotting it as I vs. V

Message Edited by sk515 on 07-18-2005 12:24 PM

[sk515]

bump

[Dennis_Knutson]

Measuring 2 channels is done by specifying something like dev1/a1:a0 (both channels of the same type) or using the DAQmx Create Channel twice for the same task. Are you doing either? If you are what happens? Do you get an error? Do you get the correct values when you do a single channel acquisition in MAX or LabVIEW? Can you post your code?

[Som Sreedhar]

Hi sk515!

Please refer to the following links that will help you in setting up the acquisition system to read current and voltage.

Taking multiple measurements with SCB-68 and PCI6036E

http://forums.ni.com/ni/board/message?board.id=170&message.id=59480&requireLogin=False

Measuring Current Using the Analog Input of a DAQ Board?

http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/82508cd693197ea68625629700677b70?O...

As Dennis mentioned, the DAQ boards read only voltage. Hence you will need to use a resistor to convert the current into voltage. Also, note that the PCI-6036E device contains a single ADC, two tasks cannot perform analog input operations at the same time. In Measurement and Automation Explorer, you can create a task to contain a voltage and current channel to setup your application.

Hope this helps

Regards,

Somendra

Applications Engineer

National Instruments

[sk515]

thanks!

[mars_itesm]

Hi everyone. I'm trying to graph the short circuit current behavior from a PV cell. The problem i have is that the NI-USB6008 DAQ only reads voltage and to actually make an accurate measurement of the short circuit current I need the resistance to be 0 or near to this value. Therefore, I can't use a shunt resistor to track any changes in this parameter. I'll appreciate any comments regarding this issue, thankyou.

[Nicholas_B]

Hi Mars,

Since the 6008 only measures voltage, the only way to determine current is to pass it through a resistor and measure the induced voltage, then use Ohm's Law to calculate current.  You can use a very small value resistor, but then you might run into the accuracy constraints of the DAQ device.  A DMM might be a better way for you to measure current.  Our DMM offerings can be found here. 

Regards,

Nicholas B, National Instruments