Yuaa Channel Organization; Operation - GE Mark VIeS System Manual

7.4 Operation

The following features are common to the distributed I/O modules:
• BPPx Processor
• Processor LEDs
• Power Management
• ID Line
• I/O Module Common Diagnostic Alarms
The YUAA I/O pack uses a switch block in each channel to configure signal flow to and from a DAC, a HART interface, a
PGA, and current sources. The following diagram illustrates the channel organization.
Settings for the switches and circuitry vary by the selected mode of operation, as follows:
• Thermocouples and voltage inputs connect through the switch block to the PGA and A/D. The PGA is set for an
appropriate gain based on the voltage span. Thermocouples are also periodically tested for burnout, where a multiplexed
set of current source and sink pulses a weak 10 microamperes current through the external thermocouple. If the
thermocouple has too high a resistance or has opened, the PGA senses the excessive shift in voltage. Voltage inputs do
not use the burnout pulse test.
• RTD inputs use the multiplexed set of current sources to pass two equal currents to IO+ and IO-, as well as across the
external resistor sensor. The third leg of the sensor is connected to RTN and ground using the switch block. The PGA
senses the voltage between IO+ and IO-, where any voltage drops on the wiring are cancelled out.
• mA inputs connect a burden resistor in the current path with the PGA and A/D to sense the amount of current flow. If the
input is internally fed, the DAC is set for 24 mA to drive the loop with the return path through the burden to ground,
allowing the external device to regulate the current. An optional HART connects a bandpass filter to the burden resistor,
sensing any tone signals sent from the external device. A switched transmit path driver also connects to the burden
resistor for modulating the voltage on the burden resistor when YUAA communicates back to the external device.
186 GEH-6855_Vol_II

YUAA Channel Organization

GEH-6855_Vol_II Mark VIeS Functional Safety Systems Volume II
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