09-03-2013 03:44 PM
Hello,
My voltage measurement VI returns 0 every 200-500 calls. This function is used to measure voltage on a shunt. When I put a breakpoint when that happens I can see on the DVM front panel (Agilent 34411A) a different voltage value. Also as it measures voltage on a shunt there's always some noise if if there's no current flow, meaning some millivolts, never 0.
Any ideas will be appreciated.
Thanks
CT
09-03-2013 04:17 PM
Are you getting an error at all when this happens? Is the driver truncating the value to 0?
09-03-2013 08:55 PM
Not getting an error. I had all VI's visible when that happened, no errors ( I had a breakpoint set in TestStand). Then I clicked "Run" again and received 0.00745236.
Thanks
CT
09-04-2013 04:27 AM
Are you using the serial port?
I have seen simlar zero readings when using the serial port. I ended up implementing a check on how many characters are read.
(Or say: the read function in that driver maybe doesn't catch a false reading (maybe due to a EMC spice on the serial line) and outputs the default (zero) value. )
09-04-2013 08:13 AM
No, the DVM is connected through USB to a D-Link hub and then to PC.
I am using XP
Thanks
CT
09-04-2013 08:54 AM
However, if you dig into the driver you will find the core reason:
the input string is not checked, so if you read (for what ever reasons) something that the spreadsheet string to array coudn't convert correctly, it will turn out as a zero value.
**bleep** happens, so you have to implement a string check (use the error out from scan from string)