Schneider Electric PM810, PM870, PM820, PM850 manual Demand Current, Thermal Demand Example

PowerLogicTM Series 800 Power Meter	63230-500-225A2
Chapter 4—Metering Capabilities	3/2011

Synchronized Demand

The demand calculations can be synchronized by accepting an external pulse input, a command sent over communications, or by synchronizing to the internal real-time clock.

•Input Synchronized Demand. You can set up the power meter to accept an input such as a demand synch pulse from an external source. The power meter then uses the same time interval as the other meter for each demand calculation. You can use the standard digital input installed on the meter to receive the synch pulse. When setting up this type of demand, you select whether it will be input-synchronized block or input- synchronized rolling block demand. The rolling block demand requires that you choose a sub-interval.

•Command Synchronized Demand. Using command synchronized demand, you can synchronize the demand intervals of multiple meters on a communications network. For example, if a PLC input is monitoring a pulse at the end of a demand interval on a utility revenue meter, you could program the PLC to issue a command to multiple meters whenever the utility meter starts a new demand interval. Each time the command is issued, the demand readings of each meter are calculated for the same interval. When setting up this type of demand, you select whether it will be command-synchronized block or command-synchronized rolling block demand. The rolling block demand requires that you choose a sub-interval. See Appendix C—Using the Command Interface on page 83 for more information.

•Clock Synchronized Demand (Requires PM810LOG). You can synchronize the demand interval to the internal real-time clock in the power meter. This enables you to synchronize the demand to a particular time, typically on the hour. The default time is 12:00 am. If you select another time of day when the demand intervals are to be synchronized, the time must be in minutes from midnight. For example, to synchronize at 8:00 am, select 480 minutes. When setting up this type of demand, you select whether it will be clock-synchronized block or clock-synchronized rolling block demand. The rolling block demand requires that you choose a sub-interval.

Thermal Demand

The thermal demand method calculates the demand based on a thermal response, which mimics thermal demand meters. The demand calculation updates at the end of each interval. You select the demand interval from 1 to 60 minutes (in 1-minute increments). In Figure 4–5the interval is set to 15 minutes for illustration purposes.

Figure 4–5: Thermal Demand Example

The interval is a window of time that moves across the timeline.

99%

90%

% of Load

0%

Demand Current

Last completed demand interval

Time

(minutes)

15-minute next

interval 15-minute interval

Calculation updates at the end of each interval

The power meter calculates demand current using the thermal demand method. The default interval is 15 minutes, but you can set the demand current interval between 1 and 60 minutes in 1-minute increments.

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