Multiplexer before USB-6002

[MikeSv]

Hello everyone. 

For a project Iam working on I need at least 120 analog channels. 

There is no need for a high sampling rate as it would be enough to read a channel every minute. 

As a DAQ with 120 single channels is extremely expensive I was wondering if it would be possible to connect a MUX before a more cheaper DAQ like the USB 6002 and if so what kind of hardware would be available for that? 

Thanks in advance, 

Kind regards, 

Michael 

[Hatef.fouladi]

if your mux have external power source (do not use usb 5 v power )
so it is possible but do not forget any useb2 just could transfer up to 100M/s data in theory and in real it is better to use any usb2 to transfer up to 30m/s data
also one of problem that you will be encounter with it is channel synchronization for solving this problem you can use trigger trick

[johnsold]

One issue with high channel count multiplexing is impedances. The series resistance of the external multiplexer may add errors due to voltage divider effects or settleing time effects.  Most multiplexed DAQs use switched capacitor muliplexers so complete characterization of how they behave with an external muliplexer may be difficult.

The USB-6002 is specified with a large input resistance (>1E9 ohms). They do not specify errors due to source impedance or settling time so you may need to do some testing. The specification mentions bias current of +/-200 pA. This may require a DC path to ground (as opposed to external switched capacitor multiplexer), but this is not spelled out. Given your slow timing requirements, settling time issues should be negligible.

There are 16:1 analog multiplexer ICs available (Analog Devices, Maxim, TI, others). One of those on each of the 8 input channels of the USB-6002 might work. Control the addressing with the DO lines. Without more information about your signals and requirements, I cannot be more specific.

Lynn