ITRON Centron, Technical Reference Manual

Page: 59 / 100

Operation: C12.19 C1SD, C1ST, and C1SL Versions
CENTRON® Meter Technical Reference Guide 49
Demand Registers
Demands can be calculated from any of the four selected energy quantities. The user can
configure up to ten demand registers.
Demand Calculations
To calculate demand, the selected quantities are accumulated over a programmable time
period (1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, or 60 minutes) depending on the programmed
demand interval length. At the end of the interval, the accumulated values are stored in
separate demand storage registers and the accumulating registers are cleared. Incremental
values for the next demand interval are then accumulated.
The maximum demand in a billing period is determined by comparing the demand values
for the most recently completed interval to the respective readings presently stored in the
peak demand registers. If the previous demand is greater than the value in the
corresponding peak demand register, the lower value (the maximum demand recorded so
far) is replaced. If the previous demand is less than the value in the corresponding peak
demand register, the maximum demand value remains unchanged. This update process is
carried out when a demand interval is completed, when a power outage occurs, when Test
Mode is initiated, or when a Real Time Rate change occurs.
The CENTRON meter demand calculations are performed using one of three possible
methods: block, rolling, or thermal emulation. The demand method is selected when the
register is programmed.
Demand
Calculation of demand is always based on rolling or block intervals. Demand calculations
use three constants; the watthour constant (Kh), the demand interval length, and the register
multiplier.
The weight of an incoming pulse is determined according to the following formula:
The demand in a given interval is the product of the number of pulses received during that
interval times the pulse weight:
The Demand value is continuously compared against the stored maximum value. If a
demand value is greater than the corresponding maximum demand, it is saved as the new
maximum demand. If the demand value is less than the corresponding maximum demand, it
is discarded. At the beginning of an interval, the current interval demand is reset to zero and
new demand values begin accumulating.