STPM01 datasheet(23/56 Pages) STMICROELECTRONICS

23 / 56 page

STPM01

Theory of operation

23/56

channels for active energy calculation. The average is implemented with the multiplex ratio

of 32:32 periods of line per channel. This means that for 32 periods of line voltage, i.e.

640ms at 50Hz, the current of primary channel is used for the calculation followed by

another 32 periods of line voltage when the current of secondary channel is used instead.

Four periods before the primary to secondary switching point a tamper detection module is

activated and it is deactivated after eight periods of line are elapsed. This means that

energy of four periods of primary channel immediately followed by energy of four periods of

secondary channel is sampled within the tamper module. We shall call those samples A and

B respectively. From these two samples the criteria of tamper detected is calculated. If four

consecutive new results of criteria happen, i.e. after elapsed 5.12s at 50Hz, the meter will

enter into Tamper State

8.10.2

Tamper state

Within this state the multiplex ratio will change either to 60:4, when primary current is higher

than secondary, or to 4:60 otherwise. Thus, the channel with the higher current will

participate in the energy calculation. Even more, the energy is not averaged by the

mentioned ratio, rather the last measured higher current is used also during 4 line period

gap. The gap is still needed in order to monitor the samples of the non-selected channel,

which should check when the tamper detected state is changed to either normal or another

tamper detected state.

Several cases of transition of the state are shown on the Figure below.

Figure 18.

Tamper conditions

STPM01 数据表(PDF) 23 Page - STMicroelectronics