Multifunction DAQ

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My sampled input picks up interference signal at 312kHz from the DAQs switching power supply on USB-6366 OEM X series DAQ device (board only). Is there a suggestion to reduce this?

THere is an approximate 25mA peak to peak ripple on the input power line of the DAQ, and an associated line in my data spectrum. I can lock on the ripple by triggering on the switching pulse on the coil of the DAQ's on-board 5V switching supply. Even with 10ohms on each differential input, connected to each other, the signal can be detected. Has anyone seen this, and dealt with it effectively? The switcher runs at 312kHz. A large cap across the power at the DAQ and a choke in the power line reduced the current ripple in the power lines, but increased the interference level.


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Message 1 of 6

Hello ELocke,


Could you give more description on what you are seeing exactly? What lines are you seeing this noise on? Is it just on one line or on multiple lines? Is the noise you are seeing at or around 312kHz on your I\O lines? Are you using a power supply from National Instruments? If so, what is the model number?



Noah | Applications Engineer | National Instruments
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Message 2 of 6

Was this problem previously solved?


We are observing a similar problem with the USB-6366.  There are two noise lines at 311kHz and 313kHz.  They are observed with a differential input on pins 1 and 2.  The lines are small but observable if the input is a short.  The lines are larger with an open circuit or with 50ohms on the input.  The lines are present when the device is powered using from AC with the included AC/DC converter.  The lines are also present when powered directly from a battery.

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Message 3 of 6

So this is only on analog input 1 and 2? Does this happen on any other lines? How large is the spike?

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Message 4 of 6

this is ancient history now, but no solution was ever found.



In channel x there were lines at 310k and 312kHz. These were traced to switching supplies on the DAQ
boards. They can be seen even when the connector was removed between the receiver board and the
DAQ card.


see attached picture of noise floor. I believe it happened on several channels that were tried. As stated in notes, I could remove the wiring and still get the lines, so not a wiring issue. 


Good luck!

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Message 5 of 6

I believe we would expect to see a ripple voltage at the switching frequency. To filter this, you could try to use an LC filter. 


What is your application? Since this forum dates back to 2013, I recommend creating a new forum post so that it will gain more visibility. 

NI Product Owner
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