GPIB seems to be maxing out current?

[pblogan]

I am running a National Instruments GPIB-USB-HS+ on some software that we use in our lab. All it does is read the voltage/current/power in from a Magtrol 6530 and display it on a VI. In the software what I'm doing is measuring fan air flow and power to get fan air and power curves. So I have an instrument panel on my VI that reads out all of the data and then I click a button to take a point, which records all of the data at that moment in time and saves it to a table/array, then when I have taken all the points that I need I click process and it outputs that table/array to an Excel data sheet template.

The issue I'm having is that it seems like the GPIB or the software has a max limit and I can't figure out why. My Magtrol is reading everything out correctly, but in the software my display will only read in the current and power if the current is under 4.5a - if it is over that then the current and power read 0, even though the Magtrol is reading out the correct values no matter how high they are. The voltage reads out consistently in the software no matter how high any of the power readings are.

Any idea what could be the issue?

[crossrulz]

Code would be helpful to help diagnose your issue.

Have you tried querying the meter through MAX and verify the data strings that are being sent out?

[pblogan]

Here are some code snippets:

Read Magtrol VI and current/voltage/power variablesVariables for Read Magtrol VIRead Magtrol VI code

[pblogan]

I have viewed the strings using I/O Trace and it looks like it's sending the correct values through, they just aren't showing up on my VI correctly for some reason.

[cstorey]

You have set the VISA read in your "Read_Magrol.vi" to read only 183 characters.  Perhaps when the readings are higher you need more characters?  I suspect when current gets >4.5A the power reading has extra digits (9.5W --> 10.1W) and your data reading scheme fails and returns zeros.  

Does the instrument response have a termination character?  I'm not sure why you rely on reading 183 chars every time.  I'd try setting it to 1024 and see what happens.  That number is just a buffer, it doesn't really need to be the exact number received.    Look at the string that is returned and see how you have to modify the parsing code to handle the longer string.  Post a sample string if you get stuck.