STPM14 STMicroelectronics, STPM14 Datasheet - Page 20

• Manufacturer Part Number: STPM14
• Description: (STPM11 - STPM14) Single phase energy metering IC
• Manufacturer: STMicroelectronics

Theory of operation
Figure 17. Tamper conditions
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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 50Hz, 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
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.
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STPM11/12/13/14