HP546xxx 'scope: Why does the number of points written to a file not match the number of points acquired?

[bpownall]

First off, I'm pretty much a LabVIEW newbie.

I'm using the HP546xxx LabVIEW drivers downloaded from the NI website to control an HP54610B oscilloscope in LabVIEW 7.1

I'm basically using the "Getting Started" VI from the library, with some modifications.

One of the modifications is to take the waveform data which is displayed on the VI's front panel and write it to an ASCII file for later use.

In the sub-VI "HP546XXX Config Acquisition", I'm using the default of acquiring 4000 data points.

The result is then digitized and send to the "HP54600A\610B Read Waveform" sub-VI.

I'm taking the waveform data which comes out of this sub-VI and writing it to a ASCII file, as mentioned above.

However, I'm getting 2001 lines of data in the ASCII file.

Why am I only getting 2001 lines in the ASCII file when I've requested 4000 samples from the 'scope?  I should note that the data in the file seems to represent the  trace on the scope well - it's not like I'm only getting the first half or last half of the trace.  I feel like I'm missing something basic.

I've also probably failed to provide some critical piece of information, so please tell me what that might be.

Bob

[BillMe]

It's probably a stretch to say this is related to this topic....BUT......

I'd look at the Programming manual for the scope and make sure it accepts 4000 point measurements. If it does, then I'd look at the SCPI command equivalent of the Config Acquisition VI and then compare it to what the LabVIEW driver is doing.

What kind of driver did you download, e.g., VISA, VXI Plug N Play, etc? If it's VISA, you should be able to look in the code to see what SCPI command is being sent to the scope.

I'd look at the Read Waveform VI also to see if there is a read count parameter that maybe defaults to 2001.

Nice to have info:
Version of LabVIEW
Type of driver (name, version, etc.)
A post of the Config Acquisition and Read Waveform VI's

Message Edited by Bill@NGC on 07-31-2007 10:14 PM

[bpownall]

Hi Bill

Thanks for the response!

The 54600 series programming manual says the ACQUIRE command takes an integer argument from 1 to 4000, so I should be OK there.

I've tried comparing the commands in the Config Acquisition VI to the programming manual, and all seems OK, at least to me.

The driver I downloaded was VISA for LabVIEW 7.0.  The drive uses the VISA Read and VISA Write commands.  You're correct - that's how I was able to look at the commands in the (for example) Config Acquisition sub-VI, see what commands were being sent, and compare the commands to the Programming Manual for the 'scope series.

The Read Waveform sub-VI has a VISA Read sub-VI with a 17,000 byte count setting near the start.  That's the only count parameter I've been able to find so far, but I'm still trying to figure out how the Read Waveform VI works.

I'm running this on LabVIEW  7.1.  I downloaded the LabVIEW 7 Plug-and-Play drivers, a ZIPped file that contained the HP546XXX.LLB LabVIEW library.  It's version 1.1, dated 20 July 2004.

How do I post the Config Acquisition and Read Waveform VIs?  (As I said, I'm a newbie...)

The 54600 series programming manual refers to "preamble data" that comes along when data is read from the scope.  The Read Waveform VI parses this preamble data in some manner that I'm still trying to figure out.  The Read Waveform VI requests the data in BYTE format, which is probably good for LabVIEW and the PC, but not so good for me to look at and understand.  I'm going to see if I can figure out how to get the data (and its associated preamble) in ASCII format, and see if maybe that sheds some light on what's going on.

Is there any other information which you think might be useful in helping me (and you) figure out what's going on?

Again, my thanks for your time in helping me.

[BillMe]

You can post the VI's simply by using the "Attachment" field below the Reply to Message box (you may have to scroll down a bit to see it).

Also, it might be worth a try to call Agilent tech support. That scope is apparently discontinued, but you might get lucky and still be able to get an answer.

[BillMe]

I also notice there are some resources on the Agilent website with example programs related to reading a bitmap from a 54620 screen. Might be helpful.