USB-6009 VI Logger scaling forces differential input mode?

[RTSLVU]

So I am back on this little monitoring project with a USB-6009.

I have six voltage points I need to monitor so I would like to use single ended mode on the 6009

A couple of of the points are DC current shunts that could have current flow in either direction.

For these I have constructed diff-amps with a 1V/Amp ouput and a 5V offset so 0A = 5VDC

I have found in VI Logger that if I set a scaling for this channel with a slope of 1 and Y-intercept of -5 it forces me to use differential input mode.

With the Terminal configureation set to RSE the error I receiver states:

Error -200077 occurred at DAQ Assistant

Possible Reason(s):

Requested value is not a supported value for this property.

Property: AI.Max
You Have Requested: 10.000000
Valid Values Begin with: -15.250000
Valid Values End with: 4.750000

This does not make sense to me as all the DAQ inputs will be seeing 0 to +10V

I guess it thinks the input voltage is going to be +/- 5V not  0 to +10V as I have set the signal imput range to?

If I set the terminal configuration to differential it is fine, but I then I am limited to four channels and I need six

The scaling should be all done in software and not effect the DAQ hardware setup, should it not? 

[Abhinav T]

Hi,

The differential mode allows you to measure a higher range of voltages because it takes a difference between 2 voltages. When you are using scaled units and specifying the Maximum and Minimum values for measurement you must use scaled units. According to your scaling, this should translate to a range of -15 to +5.

I used to following settings on my system:

Max Signal Input Range : +5
Min Signal Input Range: -15

Hope this helps!

Abhinav T.
National Instruments

[RTSLVU]

According to your scaling, this should translate to a range of -15 to +5.

This does not make sense to me, maybe I am missunderstanding the scaling?

The actual voltage I am measuring will be 0 to +10 Volts DC

The voltage will be a scaled current 1V/Amp with a 5 volt offset (0Amps=5Volts)

How would I scale this to it reads out and logs as +/- 0-5Amps and be able to use single ended input mode?

[Abhinav T]

Hi,

The range of the 6009's input is -10V to +10V in RSE mode. If you apply a scale that subtracts 5 from the reading, this changes your range to -15 to +5. Since you are measuring a signal that has a 0-10V range you will infact be measuring in the -5 to +5V range (in scaled units)

The reason why it worked in Differential Mode is because the range for differential is -20 to +20V.

If you put Max at +5 and Min at -5 your application should work.

Abhinav