voltage ref problem

[maymaythar]

Hi all, Happy Christmas and Happy New Year.

Here is my problem rearding DAQ, not really about LV but I think many of you might have experienced this kind of problem.

I have a DAQ card, 6024E. I am connecting my I/O lines (Analog/Digital/Counter) to another circuit which powered by external power source. Main voltage is 30VDC and I step it down to several levels (24V, 15V and 5V). In my circuit, I have some logic (CMOS) chip which I need to interface (connect my I/O to and from) with the DAQ card. I found that I cannot directly connect my I/O lines of DAQ to my circuit, because my 5V out from DAQ is actually 35V w.r.t. to "0V" in the other circuit. Is there any way I can interface my DAQ I/O and my circuit which run on different power source. I try using comparator, and voltage follower but wont work.

Thanks and with best regds,

maymaythar

[maymaythar]

interesting that when I change my power supply, it now can work. The ref of DAQ and my power supply become level. But the old power supply is not spoiled, it can work by itself, but not with the DAQ. I am not sure why is that happen but anyway, now everything seem to be working.

[Elijah_K]

Hey maymaythar,

Happy holidays to you as well!  That's a very unusual scenario you described.  Even though you said the first power supply is working, it would seem that if the only thing you changed was the power supply, that it must in some way be the culprit.  My only thought is that perhaps it is unable to source a necessary amount of current for the circuit you designed.  Have you used a DMM to confirm that the power supply is fully functional?

I'd be curious to know if you are able to determine why swapping power supplies helped.  Keep us informed.

[maymaythar]

Hi Elijah,

Yes it is very unsual but I am not sure why it cause the problem. But I fully checked the power supply, It is working properly and it is a new unit. I even test some circuit using that power supply and found no problem. The one I switched is the old which can work with the DAQ output.
I am thinking might be Z-mismatch but not very sure.

I'll update with the info.

Thanks for the concern.

with best regds,
maymaythar