User`s manual

XP850030 s I/O Configurations

Figure 3-9. Effects on A/D Converter Input from Adjusting Resistor Values

Then measure the voltages at VR0- and at the U2 op-amp output. Because

the currents through the input resistor and R

are essentially identical, the

ratio of the voltages across the resistors is equivalent to the ratio of the

resistances. Therefore, the gain is

Again using Channel 0 as an example, measure the voltage VREF and the

voltage at VR0+ (see Figure 3-8). Because the current into the op-amp

input is negligible, the resistance ratio of the two resistors in the voltage

divider alone determines VR0+. The value of the fixed resistor in the

divider can then be calculated based on R

bias

and the value of VR0+.

2.5

XP8500 Input (V)

A/D Converter Input (V)

Op-amp output voltage

deviation arising from

resistor variations

Out of range

A/D converter's

input voltage

limit

-VR0

-VR0V(U2)

OUT

−