User's Manual

Chapter 2 Function Reference — SCXI_Scale
NI-DAQ FRM for PC Compatibles 2-354
© National Instruments Corporation
binArray is the array of binary data for the given channel. binArray should contain
numPoints data samples from the SCXI channel. If you acquired data from more than one
SCXI channel, you need to demultiplex the binary data that was returned from the SCAN call
before you call
SCXI_Scale
. You can use the
SCAN_Demux
call to do this. After demuxing
the binary data, you should call
SCXI_Scale
once for each SCXI channel, passing in the
appropriate demuxed binary data for each channel.
scaledArray is the output array for the scaled voltage or frequency data. scaledArray should
be at least numPoints elements long.
Using This Function
SCXI_Scale
uses the following equation to scale the binary data to voltage:
The SCXI-1126 scales the binary array to frequency, using the following equation:
scaledArray [i] = [(SCXI gain) (binArray) – binaryOffset) (voltageResolution)}/
{(5 volts) (DAQgain)(gainAdjust)]
The voltage resolution depends on your DAQ device and its range and polarity settings. For
example, the AT-MIO-16 in bipolar mode with an input range of –10 to 10 V has a voltage
resolution of 4.88 mV per LSB.
NI-DAQ automatically loads binaryOffset and gainAdjust for the SCXI-1122 and
SCXI-1126 for all of its gain settings from the module EEPROM. The SCXI-1122 and
SCXI-1126 module is shipped with factory calibration constants for binaryOffset and
gainAdjust loaded in the EEPROM. You can calculate your own calibration constants and
store them in the EEPROM and in NI-DAQ memory for
SCXI_Scale
to use. Refer to the
procedure outlined in the
SCXI_Cal_Constants
function description. The same is true for
the SCXI-1141, except binaryOffset is not on the SCXI-1141 EEPROM and defaults to 0.0.
However, you can calculate your own binaryOffset using the procedure outlined in the
SCXI_Cal_Constants
function description.
For other analog input modules, binaryOffset defaults to 0.0 and gainAdjust defaults to 1.0.
However, you can calculate your own calibration constants and store them in NI-DAQ
memory for NI-DAQ to use in the
SCXI_Scale
function by following the procedure outlined
in the
SCXI_Cal_Constants
function description.
scaledArray i[]
binArray i[] binaryOffset–()voltageResolution()
SCXIgain()TBgain()DAQgain()gainAdjust()
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