07-27-2016 06:44 PM
I am dealing with LabVIEW code I did not write that defaults most of the DMM settings and need to know what these values are in order to determine the accuracy. The code is simple, Reset DMM, Configure (DC volts, autorange, absolute) and read. A typical reading is 30VDC on the 100V range. I think it defaults to 5.5 digits which means adding 10 ppm to the range accuracy for the PXI-4070/4072. I have some information scattered across many web pages but what I need is a single document showing all default values and can't find one or more for the PXI-4070/4071/4072 DMMs.
07-28-2016 08:18 AM
In the code, if you have the Context Help window open, you can select Detailed Help. In the window that opens up, you should be able to see what the default parameters are for the specific VI.
07-28-2016 10:18 AM
Your best option is to use Property Nodes to read back the values just before you call Read() (or, if you're using Fetch, before calling Initiate).
The number of permutations for the default values based on what you Configure is huge, particularly since many attributes affect one another, so we don't list them all explicitly.
07-28-2016 12:35 PM
I don't have any access to hardware for the next two weeks so I can't run anything. I would like to know the difference in defaults between the DMM configure measurement digits and configure measurement absolute for the resolution parameter when autorange is specified. According to the context help, both calls ignore the resolution parameter and use the default. For Digits the default is 5.5 digits and for absolute it is 0.001 VDC for the DC Voltage function. For Digits this means the resolution will be 00.0001 on the 10V range and 000.001 on the 100V range. But for absolute the resolution will be 0.001 for all ranges. This means the 4.5 digits range will be used on the 10V range but 5.5 digits on the 100V range. So when using the 100V range there is no difference in the setups with 5.5 digits. But on all other ranges, the number of digits will differ. My conclusion is the absolute accuracy is unacceptable (e.g. 3.5 digits on 1V range). I think both the range and digits should be specified to insure the required accuracy is met. Please let me know if you agree with my analysis.
As an aside, I wonder why we can't pass the number of bits desired (10 to 26) as an option since some specification state 3, 5 and 7 digits are possible.
07-29-2016 04:00 PM
You are correct. When using Autorange and the Absolute version of the Configure Measurement VI, measurements in the lower voltage ranges will have less resolution than measurements in the higher voltage ranges.
If you would like the resolution to be consistent across all ranges, make sure to use the Digits of Resolution version of the polymorphic Configure Measurement VI when taking autoranged measurements.