Measuring Voltage through a SCB68 pin board

[Peejay]

Hi,

I have an Analog Input coming from a power supply and going into a SCB68 pin board, which goes through labview.

And i am testing whether or not the reading i have on the power supply is the same reading that labview is processing, but 

the reading is off by  plus-minus 2.  Does the SCB board have to be grounded in order for me to have a accurate reading 

between both systems? 

Pekir 

[devchander]

Hi Pekir,

In which mode are you connecting and reading the signals?

Read this tutorial on: 

Field Wiring and Noise Considerations for Analog Signals

Which Mode Is Best for Measuring Floating Signal Sources? 

Which Mode Is Best for Measuring Grounded Signal Sources? 

to learn about the same

To know how to connect and configure the mode of measurement on DAQ card, Consult the user manual of DAQ board and signal connection diagrams.

Any further clarifications you seek, do let us know

Regards,

Dev

[Peejay]

Hi,

I grounded the DAQ board signal(channel 67)  and the readings i get are still off.  Im using the DAQ in Differential Mode and the signals are in channel a0,

which are 68(positive terminal) and 34(negative terminal).  When i run my program with the simulate signal function in labview, all the readings are

correct and i get a full sine wave, both positive and negative cycles, but as soon as i input the analog signal thats when the problem  starts.  The sine wave only shows the positive

cycle and  when I dont input any signals the flatline is at -10 instead of it being at zero. Im not sure what the problem. I tried several other different grounds and still no results.

Does this represent a malfunction in the DAQ board or is it that the overall connections are completely wrong?

Thank You

Pekir 

[RT4CY]

Hey Pekir,

If you are in differential mode, it is best to use bias resistors to remove bias currents.  The Field Wiring article talks about this as well.  If you are trying to verify the hardware, I would take LabVIEW out of the equation.  Go to Start»Programs»National Instruments»Measurement&Automation (MAX).  In MAX, locate your device under Device and Interfaces.  You can right-click and run a Test Panel to read a voltage.  Try reading off of several channels for troubleshooting purposes.  Let me know how that goes.