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problems using daq MX vs. traditional


goran

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Im using labview 7.1 and I have used traditional daq but Im going to switch to daq MX for sampling data. I have created 2 vi's, one for MX and one for the traditional daq, but they dont give me the same values/data. Any ideas how I can fix this? Se attached files for the block diagrams and front panels for the vi's.

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What kind of DAQ-hardware are you using? (Always good to know).

What kind of signals did you connect to your analog-inputs? The difference does not seem to be very large. Perhaps your inputs are drifting...

Also, you explicitly chose RSE for DAQmx, but not for your Trad-DAQ example.

Regards, Jens

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The test above is on a NI PCI-6036E daq card.

I choosed NRA becuase it gives the closest result. How can I check what method the trad-daq example uses?

I dont think its a drift in the hardware, it doesnt matter if I let the examples runs 3s or 10min, the result is the same.

We have connected pressure sensors to the daq hardware.

In column 3 for example, the result in traditional example is about 16511 and in the mx example 17320, i think that is a big difference. The 2 first columns is the preassure and the rest is voltage.

On the traditional vi 'AI Read.vi' I can get both unscaled (what im using in the examples) and scaled data, how can I scale the unscaled data from the MX vi 'DAQmx Read (Analog 2D I16 Nchan NSamp).vi'?

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There is difference where DAQmx gets the 'raw' data from, it should be mentioned in the help for that function. But the I16 output is not the raw data for an E device (it is different for an M device), to go from I16 to float you should get an array from the 'Device Scaling Coefficients' that returns per channel the polynomial components for conversion from I16 to engineering units.

post-2399-1243500403.png?width=400

Ton

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I'm not sure why your comparing raw values. Why don't you use scaled values and compare those? Use a 1.5V battery connected to a channel and compare that with both codes. I'm sure it will read the same.

Raw DAQ values are only useful when you are doing extremely high-speed DAQ and you would rather scale the values post-data acquisition. For anything less than 1kHz sample rates its unnecessary.

N.

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