6259

[Matty_B]

Hi,

I'm currently using the 6259 connected to a TBX-68 and Labview 2010.  I'm basically just trying to use it for a multimeter to get accurate current measurements, however there is something I dont understand about the examples given in Labview.

My program is set up very similarly to the "Acq One Sample.vi".  I'm using a DAQ assistant with RSE configuration.  When I connect a voltage source to a resistor which is wired to pin 68 to the TBX and pin 67 to the ground of the voltage source and measure current, I do get a reading, however the current only changes as the voltage source is changed.  If I trade out the resistor for a higher (or lower) value, the current doesn't change.  I think it has something to do with the internal shunt resistor within the program, but if I need to measure current accurately in order to determine an unknown resistance, how can I do this?

[Chris.N · Accepted solution]

Mayy_B,

Firstly, you should not be using RSE for your measurement, you should be using NRSE because you are not measuring a floating source.  More information on this can be found in this article: https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

Please note that this will change the wiring on the TBX-68 and require the negative line go to pin 62.  Also, there are no internal shunt resistors in the 6259, an external shunt resistor must be used.  This resistor should be connected between pins 68 and 62.  You will specify the resistor value in the DAQmx create virtual channel vi that is set up for the Analog Input Current task.  This should result in an accurate current measurement.  

[Matty_B]

Thank you Nunnya!  I was originally using Differential, and someone had told me to use RSE.  That gives a better understanding though.  Also I didn't realize the defualt value for the shunt resistor was an external resistor I had to supply.  I'm now getting accurate measurements! Thanks again.