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GPIB/VISA Read: too slow (50Bytes/100ms)
tiedjem
Member
10-20-2005 02:34 AM
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Hi,
I'm a newbie in using Labview and I work with the NI-GPIB-USB-HS adapter to an old 12Bit A/D converter. The vi I programed (s. Attachment) is too slow: about 1kbyte/sec. What can I do to speed up the vi? btw I also tried the "GPIB read" labview vi's, but it's quite the same.
thx
10-20-2005 10:02 AM
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here should be the Attachment
Dennis_Knutson
Knight of NI
10-20-2005 10:24 AM
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You'll need to provide a bit more information about the device you're reading from. Normally, you write a command to an instrument requesting that it take a measurement and place the results in it's output buffer. You would then read the results. To get additional results, you would have to repeat the write statement before you can do another read. You are doing a single write and then multiple reads. If the instrument behaves like other GPIB instruments, after the first read, the output buffer would be empty and the read would wait for the timeout setting while waiting for 2 bytes and then generate a timeout error because there aren't 2 bytes available for a read. If your instrument is continuously placing data in it's output buffer without a specific write command for it, it would truly be a strange instrument.
Collin M
NI Employee (retired)
10-20-2005 12:50 PM
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In additon to what Dennis said, USB is not very
efficient for very small transfers. I see you are doing a 2-byte read.
The transfer rate of the GPIB-USB-HS is about 2.5kB/s for 2-byte reads.
Increasing the transfer size will give more efficient data transfers.
10-21-2005 02:17 AM
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Thank you for your comments.
I will describe a littel bit more of my environment: the GPIB-USB-HS is connected to an 16 channel temperature measuring instrument "microlink TC16", build about 1987. So when I write a command I switch a channel with a parameter for the amplifying, then the GPIB device begins continously to talk 2 Bytes data. When I increase the read buffer (e.g. 4Bytes) I get no result, maybe the GPIB device do not understand the read request.
If there is no may to read more then 2 Bytes with one read, what can i do?
Thanks
M.Tiedje
