unrecognized headers in GPIB commands

[liam3001]

I keep getting an "unregognized header" error message when I send some very simple commands to my keithley 2400. Is it likely to be a problem with the format of my commands, which are very simple GTL, INIT, etc or the way the instrument is set up...

[Chris M]

Hi Liam,
I've been trying to understand your question in order to help you but I'd like a more information. Are you using VISA commands or interface specific commands? Are you communicating through MAX or through your own program? If you are using your own program is it labview ? Is your instrument a serial GPIB instrument? which driver and version of it do are you using? Are you using an instrument driver for the Keithley instrument. Does the instrument or the PC give the error message? any other general background info would also be helpful.

ChrisM
Applications Engineer NI

[liam3001]

Hi Chris,
Im communicating with the keithley 2400 through a CEC488 GPIB interface card. I can test the command in both VISA and direct write to GPIB mode and in all cases get the same error which is given by the instrument via a short buzz and the message "unrecognised header". Im running Labview version 7.0 and have since discovered that the GTL command (Go To Local) never worked for previous users of the instrument. Commands such as untalk and unlisten are also troublesome. I prefer to write my own programs but sometimes use parts of virtual instruments that may be available at the ni website. I have found this to be the mist useful and speedy way of interfacing any instrument and have not had any trouble with in in the past. I think thats answered a
ll your queries and I hope you can be of help.

[Chris M]

Hi Liam,
Thank you for the extra info, am I right in thinking that the GPIB card you are using, the 'CEC488' is not a National Instruments card, but uses a driver which simulates an NI 488 interface?
Your problem probably lies either in you GPIB card and PC or in the formatting of the command. Does the GPIB card work with other instruments? Are you using the most up to date version of the card's and instrument's driver software? If the GPIB card isnt an NI card I cant really help as we dont support support 3rd party card drivers. I did some research into the Keithley instrument drivers that we have on our website and they appear to be supported by Keithley, have you tried contacting them?

Chrism

[liam3001]

Hi Chris
Yes it is a third party card..and as far as Im aware it is the most up to date drivers etc. The card itself I would say is fine. Its only for specific commands that it actually has trouble. I think I can get around it by reinitializing etc from time to time and it may just require a little more "invention" with my programming..

Thanks, Liam.