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The amplifier stage of the A/D converter circuit performs two functions: (1) amplifies low
level input signals and (2) converts this input signal into a voltage range acceptable to the
A/D converter. Seven gain levels are software selectable for the amplifier stage of the A/D
circuit. To support high level input signals, the DAQ-12 provides input gain selections of
1, 2, 4 and 8. For signals requiring greater amplification, the DAQ-12 provides input gains
of 1, 10, 100 and 500. The gain setting is determined by the value written to the gain control
register.
In order to provide a full +10 volt input range and for greater overall versatility, the
DAQ-12 is equipped with a 'divide by 2' pre-scaling circuit. With the pre-scaler enabled, the
resultant high level input gain selections become ½, 1, 2 and 4 and the low level input gain
selections become ½, 5, 50 and 250. Figure 2-2 illustrates jumper J7 (Pre-scaler) configuration
options.
NOTE: The unipolar / bipolar input selection is controlled by the A/D converter and is
selected independent of the single-ended or differential input mode configuration of the
multiplexer and amplifier circuits.
J7
Disable Pre-Scaler
(factory default)
Enable Pre-Scaler
Figure 2-2. Jumper J7 Configuration
DAQ-12 Users Manual 11