Visa or GPIB manner

[Aliweal]

Dear Mr. / Madam,

I am doing a stability measurement program using Labview, and the GPIB-USB-HS connected to Keithley. But I have some questions.

1) I can read the signal coming from Keithley using <GPIB Write> <GPIB Read> <Match pattern> <Fract/EXP string to number>. I saw this method in an example on the  website. My question is why do I have to write before I read? And How can I read continuously (Using the while loop)?

2) I can also read the signal coming from Keithley using <VISA Open> <VISA Write> <VISA Read> <VISA Close> my question; What is the better way (More accurate) to read the input voltage signal <VISA> method or <GPIB> method? Why I can't just READ without write.

3) I want to plot the samples I read in a graph.  X-is time, Y-is the amplitude, but I need your hint for that??!! :).

Thanks in advance

Ali Al-Omaishi

PS: Both VISA and GPIB programs in the attachment file.

[Albert.Geven · Accepted solution]

Hi

VISA is the preferred method, because with VISA you can read and write to instruments on all busses available on that instrument.

e.g. GPIB and USB and serial.

You should open the visa connection only once in your program, perform the necessary writes and read, just before the end of your program you should call close.

On your question why to do a write if you only want to read is that the instrument has no way of knowing that you want to read, and especially what you want to read.

PS which Keithley instrument are you talking to? And is there not an instrument driver available from NI or Keithley?