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Chapter 2 Function Reference — AI_VRead
NI-DAQ FRM for PC Compatibles 2-18
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National Instruments Corporation
voltage is the floating-point variable in which NI-DAQ returns the measured voltage, scaled
to units of volts.
Note C Programmers—voltage is a pass-by-reference parameter.
Using This Function
AI_VRead addresses the specified analog input channel, changes the input gain to the
specified gain setting, and initiates an A/D conversion.
AI_VRead waits for the conversion to
complete and then scales and returns the result. If the conversion does not complete within a
reasonable time, the call to
AI_VRead is said to have timed out and NI-DAQ returns the
timeOutError code.
When you use SCXI as a front end for analog input to an MIO or AI device, Lab-PC+,
Lab-PC-1200, Lab-PC-1200AI, PCI-1200, LPM device, or DAQCard-700, it is not advisable
to use the
AI_VRead function because that function does not take into account the gain of the
SCXI module when scaling the data. Use the
AI_Read function to get unscaled data, and then
call the
SCXI_Scale function.
When you have an SC-2040 accessory connected to an E Series device, this function takes
both the onboard gains and the gains on SC-2040 into account while scaling the data. When
you have an SC-2043-SG accessory connected to your DAQ device, this function takes both
the onboard gains and the SC-2043-SG fixed gain of 10 into account while scaling the data.
When you have any SCC accessories connected to an E Series device, this function takes both
the onboard gains and the SCC gains into account while scaling the data.