ABB Industrial IT enabled REX 521 Technical Reference Manual, General page 67

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Technical Reference Manual, General
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ASCII American Standard Code for Information Interchange
CRC Cyclic Redundancy Check
CT Current transformer
DI Digital Input
HMI Human-machine interface
HSPO High-speed power output
IRF Internal relay fault
LCD Liquid chrystal display
MMI Man-machine interface
NC Normally closed
NO Normally open
PO Power output
RTC Real-time clock
RTU Remote Terminal Unit
SA Substation automation
SO Signalling output
TCS Trip-circuit supervision
VT Voltage transformer
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