VI Works Single Step at a Time, But Not When Run Normally

[rjohnston]

I'm very new to LabView and have created a simple VI to record a single measurement from my HP 34401A Multimeter over an RS 232 connection.

The problem that I'm having is that the VI only works when I run it a single step at a time (clicking the single step button until it's completed).  When I try to run the entire thing though, I get the following error:

Error -1073807339 occurred at VISA Read in Untitled 2

Possible reason(s):

VISA:  (Hex 0xBFFF0015) Timeout expired before operation completed.

After reading through the help page for that error, I tried adding a time delay, but that did not fix the problem.

(http://digital.ni.com/public.nsf/allkb/874B379E24C0A0D686256FCF007A6EA0)

NI I/O Trace didn't provide any answers for me, but I've attached a shot.  Lines 1-13 are from the single step run, the rest are from attempting to run the entire thing at once.

Can anyone please help me understand what's going on here?  Thanks in advance!

If anyone is interested:

Windows 7

LabVIEW 2009

HP 34401A Multimeter

RS 232 connection is through a USB-Serial adapter

[muks]

Please remove the flat sequence. Put a while loop around visa read

[P@Anand]

Are you sure that you will get 200 bytes of data? Why don't you try using the "bytes at the port" property to find out how many bytes available to read.

[crossrulz]

The termination character is turned on, as it should be.  That instrument puts out a termination character at the end of its data.  So you don't need the Bytes At Port in this code.

Put in a Simple Error Handler at the end of your sequence.  When the VISA Read has an error, it should tell us what the error is.

[billko · Accepted solution]

The only thing I can think of is that you are sending the remote command and then not waiting long enough for it to complete.  The manual states:

It is very important that you send the

SYSTem:REMote command

to place the multimeter in the remote mode. Sending or receiving data

over the RS-232 interface when not configured for remote operation can

cause unpredictable results.

And I think we are experiencing unpredictable results.

i don't know if you can change the command into a query by using the *OPC? command, but using that could solve it - or we could run into the same issue because of the caveat mentioned above.  Maybe you have to put a manual wait in between the remote command and the write command.

[rjohnston]

Thank you all for your help.  It is working now.  I had to manually add substantial time delays (200ms or more) between each command sent to the meter.  I suppose it is a very old device, but I feel like there must be a better way to work around this.

[Dennis_Knutson]

Why aren't you using the driver that comes with LabVIEW? It's on your palette and there are examples in Help> Find Examples under Hardware Input And Output.