User's Manual

DRAFT
Chapter 1: System Overview 21
DRAFT
©
Datamatic, Ltd. 2000 - 2005
Electric FIREFLY MIU
Meter Reading
The Electric FIREFLY MIU unit counts disc rotations, which are typically 7.2 watt-
hours per rotation. The meter reading is stored in a 32-bit register in units of 0.1
watt-hours with a rollover at 99,999,999.9 watt-hours. The sensor constant, watt-hours
per rotation, is set in the configuration data, and is typically initialized to 72 decimal (48
hexadecimal).
The meter reading tracks the electric meter mechanical registers, this includes both
forward and reverse rotations. That is, when the meter rotates forward, the meter reading
goes up, and if the meter rotates in reverse direction, the electronics reading decreases
just as the mechanical register decreases. The reverse rotation reading is also stored in a
32-bit register, which cumulates the reverse rotations in units of 0.1 watt-hours. The
reverse rotation register increases with reverse rotations; it never decreases.
Demand Data
Demand data is based on the change in the meter reading register over a demand interval.
The demand interval is fixed to 15 minutes. The demand is recorded in units of kilowatts.
Demand is only calculated on the net forward power for the interval. If there is net
reverse consumption for the interval, then that interval is discarded. The peak demand of
the current 30-day cycle that is in process and the peak demand of the previously
completed 30-day cycle are stored.
Profile Data
The unit gathers and stores consumption profile data. The individual profile data
elements are calculated from the change in the meter reading over the interval time, and
then divided by the scale factor. The profile data is gathered according to configurable
parameters, interval length, and scale factor. Valid values gathered range from + 32768 to
–32767; positive and negative consumption is monitored. The data is stored in non-