ON NI-FPGA-RT DMA FIFO COSS -TALK WITH NI-9215

[Harry potter]

I am using NI 9215 for acquiring millivolt data coming out of LEM voltage and current sensors( referenced to the power supply ground). There are 6 sensors and so 4 channels of one mod+ 2 channels of another mode of NI 9215 is used. I have connected the signal(ac) to the positive or A1+etc and negative to the power supply ground. I have also connected this ground to the COM terminal of the module. FPGA DMA FIFo based data transfer is what I am adopting. But in RT Vi I get alot of "cross-talking!!". ie: one channel of data mixes up with another channel data!! I disconnected the ground from COM terminal, still not working. Why this is happening? Can anyone help me bit on this....

[xseadog]

Hi

if i understand you description: 6 voltage channels ? Assuming that is the case,then you must be measuring the volt drop over resistors in the current sensor circuitry.

If you have coupled all negative sense signals to the negative power supply then yes you could have cross talk. In whcih case necessary to

adapt you hardware sensing solution, which could mean utisling a different type of senor module.

What frequency are you wanting to measure? 9205 module has a better resolution than 9215 but is a mux not sim.

Could you coding have an interference on the signal analysis?

xseadog

[Harry potter]

I am coupling the negative sense(A-) of the 9215 to the power supply ground. This is the ref for the ac signal , which is the output of the sensors ie: its single ended. Also this ground I am also shorthing with the COM port of the 9215. Its simultaneous ADC. But it has a conversion time of 10microseconds(from the spec) if I use all 4 channels (ie: 100Khz, simultaneous). But I am sampling it at only 100microseconds(10Khz), each channel, which is very large time!! Also, will a voltage follower at the connecting end cure this issue? Please suggest me some tips.... Its not possible to buy a new or diff module again, since funds are not there !!

[xseadog]

Don't shout

xseadog

[xseadog]

Hey

suggest you provide salient information.

What actual terminals are connect ( name them etc)

Very difficult to help you in the dark. Are we in the ether?

Are your primary signals  4-20 mA?

xseadog

[Harry potter]

No! i am not shouting

the font size became large and i accidently posted it ... so I am agin posting it:

I am coupling the negative sense(A-) of the 9215 to the power supply ground. This is the ref for the ac signal , which is the output of the sensors ie: its single ended. Also this ground I am also shorthing with the COM port of the 9215. Its simultaneous ADC. But it has a conversion time of 10microseconds(from the spec) if I use all 4 channels (ie: 100Khz, simultaneous). But I am sampling it at only 100microseconds(10Khz), each channel, which is very large time!! Also, will a voltage follower at the connecting end cure this issue? Please suggest me some tips.... Its not possible to buy a new or diff module again, since funds are not there !!

Also, is it possible to combine two modules of 9215 and give it directly to one FIFO, because here we may have to deal with different conversion times....since I am using 4 channel from one and two from the other one...

Thanks

Jeeva

[xseadog]

Hi

You are still shouting drop the bold font

have you checked out the waveform ref example?

http://zone.ni.com/devzone/cda/epd/p/id/6206

If you have 2 different conversion times then you will need to change you architecture!

Suggest 1 , if using 2 different sampling rates then use 2 FIFO.

Suggest 2, if 2nd sampling rate is disivible by first then us buffering ring.

PS

if you don't answer the questions then dont't expect help

Questions are asked to determine what you are attempting to achieve, and what you have managed.

xseadog

[Harry potter]

Hi...

I am not measuring currents driectly. here I am measuring the equivalent voltage(across a resistor) and is interfaced with 9215. Also the currents across the resisitor are small in terms of ma(it can go upto say 0.03A). Here I am sensing the  equivalent voltages and that is why I am interfacing with 9215. I hope I am somewhat clear now b :manhappy:

[Harry potter]

 I will try what you suggested. Also its first time I am using this discussion forum. Therefore I apologize if I had posted something crazy or if I am not so clear ! and I also would like to say that the large sized font/bold etc accidently happened and was not intentional....  I am not an advanced user, so my intention is to learn something and to solve some issues .

To make it more clear :

A10+ : signal((AC range is 0 to max +/- 2V)

A10- : Ground of the power supply

This is the config for all the 4 channels ie upto A13-.

From the second module of 9215, I am using A10+, A10-,A11+ and A11-. All 6 I am interfacing to a DMA FIFO.

Pin 8 is NC and pin 9 is COM. Pin 9 is connected to ground. ie: to A10- itself.Ground of the power supply.

The rest I had already expalied and I will try what you have suggeted and will get back.

[xseadog]

You may think your answers are correct.

There are from where you stand!

However i am non the wiser!  provide screen dump of your physical electrical connections.

Also screen dump of your code  (FPGA, & project )

xseadog