Current Measurement using Keithly 6485

[YogeshL]

I am using a GPIB. Is there something to do with trigger or ARM (Not sure what that is)?

[NIquist]

I took another look at the pic of you code and it looks right to me.  It really looks like you are reading something back, but it is gibberish due to a COM port mismatch and interpreting the data as zero (very low) current readings.

Try adding an indicator or probe to the serial read string before it gets changed to a numeric and see exactly what the meter is returning...

[YogeshL]

I will try that and will let you know what output I am getting. If it is in gibberish, How would you suggest me to correct that, because I remember seeing the string which was meaningless. 
Thanks for the help.

[NIquist]

Wow, if you're using GPIB I can't think of anything that would prevent your code from reading the current.  Have you tried turning on Highlight Execution (light bulb icon) to see what values are on the wires as the program executes?  I'm curious what the VISA Read is returning.  Sometimes that a great hint for what's wrong.

[YogeshL]

I tried that too and every VI were returning "ok" (That means successfully communicating with 6485) and the "Measure current VI" was showing random 10^-14 values (Note the value was different every time but in the order of 10^(-14))

[NIquist]

Open the initialize VI and use Highlight Execution or probes in there too.  I have seen issues with INIT VIs throwing errors/warnings when you have ID Query ON.  You can try turning that and RESET OFF to see if you get valid data.

Then, you want to see why that happened.  You can see that Initialize VI is sending a query that lets it determine which DMM Model you have and loads it in the User Data VISA parameter.  If this gets mixed up, you can get strange readings and sometimes that happens when old instrument drivers aren't updated, or the meter firmware gets changed.  

[YogeshL]

Sure, I will try this and will let you know, can you confirm if there isn't any problem with the configuration?

[NIquist]

Keithley (Tektronix now) Meters use a system of layers to Config > Arm > Trigger readings and a PLC (Power Line Cycle) setting to determine how long the instrument averages readings.  It can be complicated.

However, you have it set up for Immediate triggering, which should bypass all that and act much like the meter being used manually.  I wish I have one here to try out some code, but I only have a couple Keithley SMUs and that's a different animal.

From what I can see, your code should take a simple reading and pass it back to your PC.  I don't see any problem with your settings.

[YogeshL]

Thanks for the help, I will run as you suggested and will come back here with the results.

[NIquist]

A long shot, but I did see some people on the forums having issues with the Zero Check functions.  this was using the old drivers, but you can try disabling autozeroing with the Configure Zeroing in the Config palette.