ADLINK PXI-2502 - Manual (Page 26)

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• Operation Theoreym
4.1 A/D Conversion
When using an A/D converter, users should know the properties of the
signal to be measured. In addition, users should setup the A/D configura-
tions, including scan channels, input range, and polarities.
The A/D acquisition is initiated by a trigger signal. The data acquisition will
start once the trigger signal matches the trigger conditions. Converted
data are queued into the FIFO buffer, and then transferred to the host PC's
memory for further processing.
Two acquisition modes: Software Polling and Programmable Scan are
described in the following sections, including the timing, trigger modes,
trigger sources, and transfer methods.
4.1.1 DAQ/PXI-2500 series AD Data Format
The data format of the acquired 14-bit A/D data is 2’s Complement coding.
Table 4.1.1 and 4.1.2 lists the valid input ranges and the ideal transfer
characteristics.
Magnitude Bipolar Input Range
Digital
code
FSR ±10V ±5V ±2.5V ±1.25V
LSB 1120.78uV 610.39uV 305.19uV 152.60uV
FSR-1LSB 9.998779V 4.999389V 2.499694V 1.249847V 1FFF
Midscale +
LSB
1120.78uV 610.39uV 305.19uV 152.60uV 0001
Midscale 0V 0V 0V 0V 0000
Midscale -
LSB
-1120.78uV -610.39uV -305.19uV -152.60uV 3FFF
-FSR -10V -5V -2.5V -1.25V 2000
Table 4.1.1 Bipolar Input Range and Converted Digital Codes
Magnitude Unipolar Input Range
Digital
code
FSR 0V ~ 10V 0 ~ +5V 0 ~ +2.5V 0 ~ +1.25V
LSB 610.39uV 305.19uV 152.60uV 76.3uV
FSR -
LSB
4.999389V 2.499694V 1.249847V 1.249923V 1FFF
Midscale +
LSB
5.000611V 2.500306V 1.250153V 0.625076V 0001
Midscale 5V 2.5V 1.25V 0.625V 0000
Midscale -
LSB
4.999389V 2.499694V 1.249847V 1.249923V 3FFF
-FSR 0V 0V 0V 0V 2000
Table 4.1.2 Unipolar Input Range and Converted Digital Codes