I design a labview program to control Agilent E5072C network analyzer. When I want to get value from this instrument, I use the "VISA read" VI which listed in the block plate. However, the value read by this VI is last time measurement value. For example, last time the read value is 1.0 db and this time the measurement value is 1.2 db. But when I use "VISA read" VI to fetch the value, it is 1.0 db. Agilent also provide a VI for this device to read measurement value, and it alway read correct value. so could someone tell me why? do I need do any action before read value from this instrument if I want to use "VISA read" VI instead of Agilent VI?

You are probably reading it too quickly. By reading it in NI-MAX, you are doing it by hand, so it takes longer. When you do it programmatically, it is "instant". Try using the *OPC? command to turn your command into a query. It will then return a "1" in the read buffer. Read the "1" and then do the fetch command. To Dennis: I've had bad experiences with manufacturer-supplied drivers to the point where I don't even try to use them any more. But if Agilent is as anal about their drivers as they are about their manuals, they should be no problem. 😄

The value read by visa read VI is not correct!

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ok. so I should type command like"*OPC? :CALC1:MARK1:X?;Y?" before read value?

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You still have not looked at the code in the driver?

And why did you mark this question as the solution?

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Author

In my program, I use ":CALC1:MARK1:Y?" to fetch the measurement value. I use read command to got the value. However, the device need some time to move the value from memroy to output area. So I read it too fast. After add "*OPC?" command before read command then the value is correct.

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LabVIEW

The value read by visa read VI is not correct!

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