ITRON Centron, Technical Reference Manual

Page: 60 / 100

Operation: C12.19 C1SD, C1ST, and C1SL Versions
50 CENTRON® Meter Technical Reference Guide
Block Interval Demand Calculation
Block Demand calculations are based on user-defined interval lengths. The demand is the
total energy accumulated during the interval divided by the length of the interval. At each
end of interval (EOI), demand calculations are made and EOI can be displayed on the LCD.
For block interval, demand calculations are made at the end of each completed demand
interval. This method is similar to the way mechanical demand meters operate. As load is
applied to the demand register, an indicating pointer and maximum demand indicator are
driven upscale. At the end of each interval, the indicating demand pointer is returned to the
zero position, and the maximum demand pointer retains its highest or maximum position.
Rolling/Sliding Demand Interval Calculation
A selected number of subintervals make up the demand interval. At the end of each
subinterval, new demand calculations occur based on the last full demand interval and EOI
can be displayed on the LCD.
The following quantities can be selected for rolling demand: W d, W r, W net, and W uni.
Block interval demand calculation is subject to peak splitting, whereby it is possible for an
electricity consumer to manipulate the load for limited periods within the demand interval.
The registered demand reading will be less than the actual maximum demand of the load.
To counter this situation, the concept of rolling demand was introduced. Rolling demand is
calculated as follows:
1
For illustration purposes, assume a 15 minute billing demand interval with three five-
minute subintervals has been selected. Then, at any given moment, the meter has three
complete sets of five-minute information available for demand calculations.
2
At the end of the present five-minute subinterval, the information on the oldest five-
minute subinterval is discarded, and demand calculations are performed on the three
newest sets of subintervals.
3 If the billing demand interval is 30 minutes with five-minute subintervals, then six sets
of five-minute information or updates will be used for calculating previous demand.
Thermal Emulation
The CENTRON meter will emulate the response of a thermal demand meter. This type of
demand calculation is approximated exponentially. The meter will record 90% of a change
in load in 15 minutes, 99% in 30 minutes, and 99.9% in 45 minutes. The four characteristics
of a thermal demand meter that the CENTRON meter will emulate are:

Arithmetic phase summation

Continuous rolling average demand

Response calibrated to RMS values

No End-of-Interval (EOI)