Rockwell Automation 1404-M4_M5_M6_M8 Powermonitor 3000 User Manual, Firmware rev. 3.0 or LATER - Manual (Page 36)

36 Publication 1404-UM001F-EN-P - November 2009
Chapter 3 Powermonitor 3000 Unit Operations
The utility may provide a pulse that indicates the end of each demand
interval. The utility updates the demand value at the end of each
interval and maintains the highest value obtained during any interval.
This method is known as thermal demand. You may set up a power
monitor to determine its demand interval from the utility pulse. To
accomplish this, connect the utility pulse to status input #2 and make
the appropriate settings in the Advanced Device Configuration.
If the utility does not provide a demand interval pulse, you won’t be
able to synchronize with the utility to control your demand. In this
case, you may use the sliding window method. This method breaks
the demand interval into many sub-intervals and updates the demand
value at the end of each sub-interval. For example a five-minute
interval might be divided into five one-minute sub-intervals. The
demand for each one-minute interval is calculated and at the end of
five minutes the average value of the sub-intervals is computed to
obtain a demand value. At the end of the sixth minute, the value for
sub-interval one is discarded and a new demand value computed
based on sub-intervals two through six. In this way a new five-minute
demand value is obtained every minute. The maximum value is then
maintained as the peak demand. This method approximates the actual
demand the utility measures.
How can you minimize your peak demand in order to reduce your
utility demand penalty charges? One way is to measure the power
being used and project the demand level at the end of the interval.
This method permits you to reduce power consumption when the
projected demand reaches a predetermined threshold, thus preventing
the final demand from exceeding the desired level.
Projected Demand Calculation
Select the best projection method for your system by comparing the
projected values from each method with the actual demand at the end
of the interval. The three methods of projecting demand are described
below.