Rockwell Automation 1404-M4_M5_M6_M8 Powermonitor 3000 User Manual, Firmware rev. 3.0 or LATER - Manual (Page 35)

Publication 1404-UM001F-EN-P - November 2009 35
Powermonitor 3000 Unit Operations Chapter 3
Configurable Energy Counter Rollover
You may configure the number of digits at which energy values roll
over to zero. The parameter range is 4
… 15 digits.
Configure this setting in Advanced Device Configuration by using the
display module or by writing to the Advanced Device Configuration
table on
page 196 .
This setting lets you optimize the energy counter rollover for use with
applications that support a limited number of significant digits. For
instance, the display module supports a resolution of five significant
digits. The Trend Log, which is used for automatic data re-population
in some energy logging applications such as RSEnergyMetrix, supports
twelve significant digits with eight digits of precision.
Demand Calculation
A typical industrial utility bill includes not only an energy (or kWh)
charge but also a Demand charge. Demand is equal to the average
power level during a predefined time interval. Some power providers
may base demand on current, VA, or VARs instead of kW. This interval
continuously repeats and is typically between five and 30 minutes in
length. The formula for kW demand is shown below.
Usually, a utility rate tariff includes a peak demand charge,
determined by the peak demand that occurs during a specified period,
which may be one month, one year, or some other duration. As a
result, only one occurrence of a high demand level can have a
long-term effect on your utility bill. The peak demand value indicates
to the utility the reserve capacity they need to satisfy your short-term
power requirements. The peak demand charge helps to pay the utility
for maintaining this instantaneous capacity.
The power monitor computes demand levels for watts, VA, amps, and
VARs, and provides three different methods for projecting demand.
Demand
1
T
--- P t ( ) t d
t
t T +
∫ • =
T = Demand interval duration
t = Time at beginning of interval
P(t) = Power as a function of time