ZWorld Exp-A/D12, User Manual

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XP8500 I/O Configurations s 21
Jumpers pins 1–2 of both headers J1 and J2 are used to select the absolute-
conversion mode where the input signal is compared against an accurate
fixed voltage reference. With this setting, 2.5 V from the precision voltage
reference goes to both the A/D converter chip and to the op-amp bias
networks.
Jumper pins 2–3 on both headers J1 and J2 are used to select the ratiomet-
ric conversion mode where both the voltage reference and the input will
fluctuate with fluctuations in power because they both use the same power
source. With this setting, a voltage divider derives 2.5 V from the analog
+5 V supply for the A/D converter chip, and the 5 V now goes to
the op-amp bias networks. (The 2.5 V from the voltage divider cannot
power the op-amp bias networks directly because it is not a low-impedance
source and the op-amp bias networks would put too large a load on the
divider.)
Using Analog-to-Digital Converter Boards
These steps summarize how to use the A/D converter boards.
1. Send a reset command to all boards on the PLCBus.
2. Place the address of the A/D converter board on the PLCBus.
3. Read an input channel, allowing time for the multiplexer to settle and
for the digital output to be determined.
4. Allow the controller to use the digital information to calculate a
meaningful value for the quantity measured.
5. Use the data to control relays, switches, or other devices with the
controller.
These steps rely on software drivers in Dynamic C function libraries. Use
DRIVERS.LIB
and
PLC_EXP.LIB
for controllers with a PLCBus port.
The XP8500 will also work with BL1400 and BL1500 controllers.