How do I fix a VISA Read error?

[Matt_@_ICS]

I am tryinging to hook up my radiometer to the computer so I can dump all the data it collects into Excel.  I have Windows XP (32 bit) and LabVIEW 8.5.1 and I just received this LabVIEW VI from the company that made the radiometer.  I keep getting the same error message everytime I try to run the VI. 

Error -1073807339 occurred at VISA Read in ILT1700.vi

Possible reason(s):

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

I know I have the radiometer hooked up correctly and I am using the correct Comm Port.  Next I thought it might be a driver issue, so I downloaded the full NI-VISA 4.4.1 driver package.  Again I keep getting the same error message.  I get the same error message even when I disconnect the radiometer from the computer.  How do I get the the computer and the radiometer to communicate?

[RavensFan]

Does the radiometer continually send out data, or do you have to send it a command code first?

Have you tried opening up a session of hyperterminal to see what if any data is coming in?

In your loop, it looks like you are reading continuously 1 byte at a time until the line feed character comes in.  You can enable the termination character of the serial port and set it for LF.  Then you can read a large number of bytes.  When the LF comes it, the VISA read will terminate itself and send the entire string on.  No looping would be necessary.

[Dennis_Knutson]

The first question is how do you know that it is hooked up correctly? Can you read data with a program such as Hyperterminal?

Second, that program you posted is a mess.

[Jeremy_B]

The default VISA timeout is 2 seconds, so your program is missing a byte and timing out.  You might want to log your serial port traffic to see the actual data coming through.  Portmon is a fantastic tool for debugging serial applications: http://technet.microsoft.com/en-us/sysinternals/bb896644.aspx