RIO 2.4.0 Calibration Mode

[Stephen_Moore]

Hi,
How does the calibration mode available in RIO 2.4.0 get the calibration values?

Are calibration values obtained when in raw mode the same, and do the calibration values change with time/temperature/other or are they a fixed item purely defined by an external calibration process and the interaction between the module and the FPGA.

What penalties are there associated with using calibrated mode rather than raw mode.

If running the cRIO system for several weeks/months at a time and the calibration values are "live" does the calibration mode periodically update the calibration values?

Also the NI 9206 has "LSB Weight" and "Offset" for each of its four ranges, it also has "Linearization Coefficient 1", "Linearization Coefficient 2" and "Linearization Coefficient 3".
What are the "Linearization Coefficient" values used for?  There is no provision for them in the Binary to Nominal vi.

Any help or a better explaination on calibration constants for cRIO modules will be gratefully accepted.

Cheers
Stephen

[Bassett_Hound]

HI Stephen,

The Calibration values are read from the same location from the C series modules when using Fixed Point Calibrated data or when using the I/O property nodes for reading LSB Weight and Offset.  The advantage of using Fixed Point Calibrated data is that the math to use the calibration information and convert the ADC data to Engineering units is done for you and available on the FPGA.  When using RAW or binary data you must read the LSB Weight and Offset yourself and perform the Math to convert to Engineering units on the Host PC or perform the math on the FPGA yourself ( which is not trivial ).  The actual calibration values for LSB Weight and Offset are static and defined by and external calibration procedure that is ran during manufacturing of the module, or when its returned to NI for calibration (there is also an external procedure that can be ran in a cDAQ chassis for some C series modules. 

In general, using Fixed Point data uses about the same amount of FPGA Resources as using Binary IO nodes along with the IO Property reads for LSB Weight and Offset.  The following KnowledgeBase: Using Fixed-Point Data with CompactRIO and LabVIEW FPGA has several links with additional information on Fixed Point data.

Regarding the Linearization Coefficients for 9205/9206 modules, they are not taken advantage of when using Fixed Point Data at this time.  You can find an example using Linearization Coefficients in the Shipping examples for the 9205 at the following location:

C:\Program Files\National Instruments\LabVIEW 8.5\examples\CompactRIO\Module Specific\NI 9205\NI 9205 Basic IO

Let me know if you need any additional information or need clarification on any topic.

Regards,

Basset Hound