06-05-2013 10:48 PM
Hi,
I have a problem with ni5733 (Digitizer Adapter Module for NI FlexRIO). I am generating a 100KHz sinewave signal using a signal generator and trying to read that using ni5733 (mounted on my FPGA NI 7965 flexRIO) .
To make sure that my readings are OK , I have also connected the output of signal generator to a digital oscilloscope using a BNC.
Here is the problem. When the output of signal generator is only connected to oscilloscope , it shows correct amplitude of the signal ( for example 1.4 Vpp) . But when the signal generator output is connected to both oscilloscope and the NI5733, the amplitude reading shown in the oscilloscope drops !!! ( for example from 1.4Vpp to 1Vpp). Also I found that this is some how frequency dependent and if I lower the frequency to 10kHz it drops less ( for example from 1.4Vpp to 1.3Vpp).
I was wondering why this happens. Is this a problem with my NI 5733?
06-06-2013 05:49 PM
Hi alireza,
Depending on the impedance of your devices, you'll get a voltage divider effect to some extent when splitting your output signal. The dependence on frequency output may be a result of some parasitic capacitance or similar non-linear characteristics of your connections/setup.
For example, the 5733 has a 50 Ohm impedance. What kind of probes are you using? How are you splitting the signal? Is your oscilloscope set to high impedance?
Regards,