Should I use much bigger bias resistors?

[vivisui]

I intend to use differential mode with bias resistors to measure signals. However, the source impedance of my ac coupled signal source is quite high(10 Mega ohm-30 Mega ohm), what is the range of the value of the bias resistors should I consider? Thank you.

[johnsold]

Look at the manual for your DAQ device.  The bias current is a characteristic of the input circuitry of the device and does not depend on the source impedance.  Of course the bias resistors parallel your source and may load its output, producing an error.  If this occurs, you will need to add signal conditioning circuitry (high input impedance buffer amplifier) between your signal source and the DAQ device.

Lynn