03-02-2009 09:07 PM
Hello,
I'm using the DAQ Assistant VI to read an analog input voltage from a National Instruments PCI-6221 card. I'm reading the voltage from pin AI0. I supply a voltage directly to this pin from a DC power supply, but the voltage measurement obtained from the DAQ Assistant is incorrect - it seems to be scaled by a factor of about 1/3. For example, if I supply 4 Volts to pin AI0, the DAQ Assist reads 1.43 Volts. I used a multimeter to confirm that the voltage at pin AI0 is in fact 4 Volts, and so I know the problem is with my LabVIEW program and not my power supply.
Here are the steps that lead to my problem:
1. In the block diagram, I insert a DAQ Assistant block.
2. In the Properies of the DAQ Assistant, I select Analog Input->Voltage
3. I select channel ai0
4. I click "test" in order to test the channel
5. The voltage is shown to be 1.43 Volts, even though 4 Volts is being supplied to the pin (this is confirmed with a multimeter).
6. To ensureI click OK to finish configuring the DAQ Assistant. I run the program and plot the voltage. The plot also shows 1.43 Volts.
Does anyone have an idea why this may be occuring. I've spent a good 4 hours trying to diagnose this and haven't found anything.
Thanks,
Abed Alnaif
Solved! Go to Solution.
03-02-2009 09:22 PM
03-02-2009 09:27 PM
03-03-2009 08:58 AM
Thanks so much for your help. I used MAX, and found out that the issue is that I had specified differential voltage, but I should have specified RSE voltage.
However, now I have a different issue: When I apply a voltage to one pin, MAX also shows a voltage on other pins.
For example:
1. I apply a DC voltage of 4V to analog input pin ai0.
2. In MAX->Text Panels..., I select Channel Name = Dev1/ai0 and Input Configuration = RSE
3. I click Start, and the chart shows the correct voltage (4V)
4. I change the Channel Name to Dev1/ai1and Input Configuration = RSE
5. The chart shows a noisy voltage reading between 1.45 and 1.5 V, even though no voltage is applied to pin ai1
6. When I change the voltage on pin ai0 to 2V, the voltage reading on pin ai1 changes to 0.63V
7. Using my multimeter, I confirm that there is in fact 2V on pin ai0 and 0V on pin ai1
Does anyone know why applying a voltage to pin ai0 causes a voltage reading on pin ai1?
03-03-2009 09:03 AM
03-03-2009 09:42 PM