Schneider Electric PM820 User Manual

© 2011 Schneider Electric. All Rights Reserved.

In the block interval demand method, you select a “block” of time that the power meter uses 
for the demand calculation. You choose how the power meter handles that block of time 
(interval). Three different modes are possible:

•

Sliding Block. In the sliding block interval, you select an interval from 1 to 60 minutes 
(in 1-minute increments). If the interval is between 1 and 15 minutes, the demand 
calculation updates every 15 seconds. If the interval is between 16 and 60 minutes, the 
demand calculation updates every 60 seconds. The power meter displays the demand 
value for the last completed interval.

•

Fixed Block. In the fixed block interval, you select an interval from 1 to 60 minutes (in 
1-minute increments). The power meter calculates and updates the demand at the end 
of each interval.

•

Rolling Block. In the rolling block interval, you select an interval and a sub-interval. 
The sub-interval must divide evenly into the interval. For example, you might set three 
5-minute sub-intervals for a 15-minute interval. Demand is updated at each sub-
interval. The power meter displays the demand value for the last completed interval.

Figure 4–4 below illustrates the three ways to calculate demand power using the block 
method. For illustration purposes, the interval is set to 15 minutes.

15 30 45

1 5

30

45

60 

1 5

30

45

20

35

40

25

P

LSD1

10131

Demand value is the 
average for the last 
completed interval

Demand value is 
the average for 
the last 
completed 
interval

Demand value is 
the average for 
the last 
completed 
interval

Time
(sec)

Time
(min)

Time
(min)

Calculation updates 
every 15 or 60 
seconds

Calculation updates at 
the end of the interval

Calculation updates at the end of 
the sub-interval (5 minutes)

15-minute interval

15-minute interval

15-minute interval

15-min

15-minute interval