STPM11 datasheet(22/45 Pages) STMICROELECTRONICS

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Theory of operation

STPM11/12/13/14

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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. It is

deactivated after eight periods of line have 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 detection is calculated. If four consecutive new

results of criteria happen, i.e. after elapsed 5.12s at 50 Hz, the meter will enter into Tamper

State

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 is used in

the energy calculation. 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 in the Figure 17 - below

The detected tamper condition is stored in the BIT signal. This signal is connected to the

SDA-TD pin. When this pin is low, a tamper condition has been detected.

Figure 17.

Tamper conditions

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