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Re: GPIB test on HP8510C electrical-optical calibration


From: Stefan Mahr
Subject: Re: GPIB test on HP8510C electrical-optical calibration
Date: Sun, 14 Jul 2013 13:21:27 +0200
User-agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130623 Thunderbird/17.0.7

>> Does it happen with large data only or also when reading less
>> points? If it crashes only with large data, please try to figure
>> out the limit.
> No way of reducing the number of points, it would make it useless
> for a microwave network analyzer.

Are you willing to debug the issue or do you simply expect a working
solution? If so, you should keep going with MATLAB.

However, there are some instruments that can not output all data at
once. It's a common way to read out in several steps.

> The problem with the gpib_read is the format in which it returns the
> data.

Why do you think the output format of gpib_read is a problem?

If your VNA returns 1Mpoints, it's basically the same data as generated
by code below:

  a = repmat (uint8("0.12345678E00,0.87654321E00\n"),1,1e6);
  a = char (a);
  b = strread (a,'%f','delimiter',',');

Well, strread takes some time, but that's not related to gpib_read.

> As I said, things with outputs that are only a few bytes it is ok...
> say a multimeter, a microwave generator is ok.
> But for a modern VNA it is a lot of data...

If you want to change the output format of your VNA it's up to you to do
so. See HP8510C manual:
  (GPIB Command: FORM2) 32-bit IEEE 728 floating point format.

I don't find any documentation of IEEE 728 floating point format. Some
of my instruments return floating points in IEEE 754 format, so it's
trivial to convert the uint8 array to single or double by 'typecast'
after stripping the GPIB biary format headers.

> I suspect something is being lost... i am getting half arrays

How much bytes your VNA sends with your test case?
How much elements you get from gpib_read?



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