ZWorld Exp-A/D12, User Manual

Page: 63 / 111

Exp-A/D12 I/O Configurations s 63
The A/D Converter
The A/D converter chip, a 12-bit LTC1294, can be programmed to convert
a signal at one of its input pins in either of two modes: bipolar or unipolar.
• Bipolar Mode—input range -2.5 V to +2.5 V, output range -2048 to
+2047.
• Unipolar Mode—input range 0 V to +2.5 V, output range 0 to 4095.
If necessary, a resistor network can be used to scale a voltage input to the
required range. Otherwise, when an input voltage falls outside the range,
the chip will report its maximum or minimum value. If the onboard
resistor networks, RN2 and RN3 (which are not normally installed), are
used, connect EX1 (on Wago connector H1) and EX4 (on Wago connector
H2) to GND, and connect the input voltage source to the input header with
an appropriate resistor.
The A/D converter chip’s reference voltage comes from either a precise
2.5 V reference (from U1), or from the “ratiometric” reference voltage.
(When R7 = 0 and R3 is absent, the ratiometric voltage is equal to VQ+,
which is very close to V+. This is the factory setup.)