Measure two analog sinus signals (kHz range) simult. not possible (NI USB-6001)?

[DPM@ch]

In a simple test-setup with NI USB-6001 I tried to measure two sinus signals (both have same frequency around 1 kHz). One comes from a function generator, the other is a sensor-signal (which should have a phase offset and a lower amplitude). I can measure both signals and get the expected behaviour. But if I try to measure both signals using two AIs at the same time, my sensor signal suddenly has a much higher amplitude, and close to a resonce frequency the sensor signal drops (it should increase). I don't understand why this is happening. I guess it has to do with the multiplexer. We need to buy a better DAQ anyway, so we could chose a DAQ with simult. AIs - but I don't know, if this would really solve the issue. Any ideas?

[Henrik_Volkers]

Try to measure with the soundcard , two channels , higher samplerate, higher resolution AND simultanious sampling instead of multiplexing.

input circuit would be from input: a decoupling cap (470nF - 2µF , foil) , two anti-parallel red LEDs (1.8V protection), (optional a buffer amplifier) , a voltage divider ...

jepp a DAQ with simultanious channels help 🙂    and a propper input .. see the input circuit of the 6001