Measure DVM functions returns 0

[Cimteker]

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

[crossrulz]

Are you getting an error at all when this happens?  Is the driver truncating the value to 0?

[Cimteker]

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

[Henrik_Volkers]

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. )

[Cimteker]

No, the DVM is connected through USB to a D-Link hub and then to PC.

I am using XP

Thanks

CT

[Henrik_Volkers]

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)