binary acquisition and accessing of data

[abdulrahman]

Hello,

I have a problem which has me totally confused.
When I acquire data with "cont Acq&Graph Voltage-To file(binary).vi", and then attempt to read this data with "read binary file.vi", what is read has no relevance to what was acquired. I have no clue as to why this is..

It is as if what is stored is of a different type to what is stored. I often see the graphed material from the stored binary file showing valued like 1.5e+250!!!

Please help ASAP.

Thank you in advance.

I have labview 7 express.

[Russell]

Hello,

The data that is saved to file is not only in a binary format, but it is the actual binary codes sent back from the DAQ board's A/D converter. These integers have not been scaled according to the range that the acquisition was set up for which depends on the gain that the DAQ board was configured for.

The gain is set based on the "input limits" you choose for AI Config. The DAQ board will be configured for the closest gain that applies to the input limits you specified. You can see a list of the available gain settings in the user manual.

Use the "Hardware Config" VI (which is called by AI Config) to determine the gain setting that was selected based on the "input limits" Hardware Config has an output cluster that contains two values you will be
interested in, Polarity and Gain. If polarity is Unipolar, the range of the A/D converter is 0 - 10V divided by the Gain. If the polarity is Bipolar the range of the A/D converter will be -5 - 5V divided by the Gain. There is more information about this in the user manual as well.

So, if you have a 12-bit DAQ board and the gain was 1 and the polarity is unipolar, the A/D converter range is 0 - 10V. The binary values need to be scaled by this range so that 0 = 0V and 2^12 - 1 = 10V.

Second, if you have more than one channel in the scan list, the channels are interleaved such that for two channels, the first binary value would represent the first channel, the second binary value would represent the second channel, the third value would represent the next first channel sample...etc.

I hope this helps. Let me know if you have any questions.

Russell
Applications Engineer
National Instruments
http://www.ni.com/support

[tamchik]

Hello,

I use NI DAQCard-6024E(PCMCIA). When using Cont Acq&Graph Voltage - To File(Binary). vi and then read data file using Graph Acquired Binary Data.vi , I get raising signal instead of constant. Maybe I get sum of signals (for example, previous loop data  plus current loop data)?

Thanks in advance,

tamchik

[devchander]

Answered here