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 | Enable Pre-Scaler |
(factory default) | |
Figure 2-2. Jumper J7 Configuration