CrossTalk and Baseline Shift in Mux80 | LabJack
 

CrossTalk and Baseline Shift in Mux80

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fieryfire
fieryfire's picture
CrossTalk and Baseline Shift in Mux80

Hello,

I am using the Mux ADG408 the same one that is being used in the Mux80. I set the stream settling time as 9.5uS which i suppose is the default as i am try to stream from 79 channels at 1000Hz each. The problem i am facing is that, When the stream settling time is set at 9.5uS, there is a signal duplication arriving in AIN(n+1) and AIN(n+2) when there is a signal in AIN(n). But this seems to be reducing when i set the stream settling time to 50uS. But the problem with 50uS is that i will not be able to get the 78 channels at 1000Hz (which is our requirement) since the error STREAM_SCAN_OVERLAP error (errorcode 2942) appears. which is normal as 50uS x 79 = 3950uS or 3.95mS which is much higher than the acquisition rate per channel of 1sample/mS. 

I suppose, the signal duplication has got something to do with the load capacitor i placed at 100nF. Would there be abny issue, if i remove this load capacitor for the multiplexer. Could you please advise the use of the load capacitor was used at Mux80 and its optimum value for our project? Note: I have tried to keep the original settling time for 9.5uS and i used the scanlist names to call one channel from each multiplexer and a cycle through all the channels that way. This way the cross talk to AIN(n+1) is removed but there is still a baseline change affect on AIN(n+1) and AIN(n+2), which appears to come from AIN(n)

 

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LabJack Support
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Try testing with VS and GND,

Try testing with VS and GND, rather than your signals, to see if it is a problem with your signals or your mux circuit.  Do VS as your first reading and then GND on the 2nd channel, and see if the readings from the 2nd channel are good.  Are the readings from the 2nd channel about the same whether the 1st channel is connected to VS or GND.

 

On the Mux80, COM from each mux chip is passed directly to the connectors.  No series or parallel components added.  So COM from each mux chip connects directly to an AIN on the T7 with no added resistance or capacitance.

 

Per Table A.1.8, with a stream at >60 ksamples/second the interchannel delay is 8 us with default settling.  The settling time (STREAM_SETTLING_US) in this scenario is 6 us, as there are also other things that need to happen during the sampling interval.