User's Manual

Universal Metering Transponder for kV2c™ Meter User Guide 9
CHAPTER
2
F UNCTIONAL D ESCRIPTION
This chapter provides an overview of the TWACS
®
system, explains how the
Universal Metering Transponder for the GE kV2c meter (UMT-C-KV MP)
interfaces with the TWACS system, and describes the functions of the transponder.
This user guide provides feature and functionality information for Firmware
version 2.00. Enhancements since version 1.20 include, but are not limited to:
• Addition of EMTR-3-KV interface (multiport)
• New module type number - 101
The kV2c meter may hereafter be referred to as kV2c, kV2c meter, or meter.
UMT, UMT-C-KV, transponder, and module refer to the DCSI UMT-C-KV MP.
Time Synchronization
The Master Station is synchronized to an official US reference atomic time clock.
The Master Station sets the time in each of the SCEs, and the SCE broadcasts the
time to all the RCEs. TWACS communication introduces a fixed time difference
(offset) between the Master Station clock and the RCE master clock.
In addition, a free running Real-Time-Clock (RTC) is provided in the UMT-C-KV
as an alternate time base for maintaining the time when the RCE experiences a
power down or an interruption. The RTC maintains the RCE time (during an
outage) for a period of no less than 24 hours. This RTC is a Secondary Time Base
for the RCE and is accurate to within 17.5 seconds per day. The RCE uses the RTC
time for time-stamping an event when the power is restored. It also maintains all
timing functions until the RCE is again in time sync with the SCE transmitted time
sync signal. Each time the RCE hears the time sync broadcast, it compares its
master clock time with the SCE time. If the offset between SCE time and the
master clock time does not exceed the threshold limits (± 15 seconds), they are
considered to be operating in synchronization.
The UMT-C-KV internal Serial Date and Serial Time registers are volatile and are
initialized at power-up. The UMT-C-KV updates its Serial Date & Time registers
when it receives the Set RCE Date/Time command. The Set RCE Date/Time
command, normally sent every fifteen minutes from the CCE to the SCE,
synchronizes the SCE clock to the CCE clock. To update serial date and time, the
SCE sends the Set Date/Time command automatically to the UMT-C-KV.
Certain UMT-C-KV functions are not performed if the Serial Time is invalid.
TWACS uses Serial Time Units (STU) as measures of time. Each STU equals 2.5
seconds, with midnight equal to zero.