Best Regards,
Im having difficulties with a measurement of DC Voltage using NI DAQ USB 6009. What Im trying to do is a Wheatstone Bridge, and I want to read the Voltage between the resistors and proccess it on my PC. Since one of my problems was the match of impedance between the output of the bridge and the input of the DAQ 6009, I decided to use a JFET Operational Amplifier with 10x12 ohms of input resistance and low output impedance as a Voltage Follower. This allows me to couple the signal in a better way, because I reduce the resistance of the voltage source. Then I connect that signal to the input of the DAQ 6009. Also I tried connecting two 100kohm between the outputs of the OpAmp and the grownd of the DAQ 6009 (Im using the channel 0 on Differential mode).
Now, the other problem that Im having is that when I plugged the DAQ 6009 to the PC, y do the RUN Test Panels, and choose Differential mode, Device 1, channel 0, and I see that the signal is oscillating, and I dont know why, because if I take a multimeter I get a DC Voltage signal, that variate as I change the value of one of the resistance of the bridge. Then I tested the channel plugging in only just a 9V battery and then I get a steady measurment in the test panel. So, I dont know why the DAQ USB 6009 is getting the noice from, or what is causing it, beacuse my voltage signal is fully DC. Its maximum value is around 9 Volts, and I see that it changes as I vary the resistance, but it always oscillate, and the maximum value of the oscillation is the actual DC voltage that it should be measuring. I hope someone can guide me, because I dont want to even think that the card is damaged. Thanks for your attention! Attached is a pic of the oscillating signal.
