STPM01 datasheet(25/60 Pages) STMICROELECTRONICS

25 / 60 page

STPM01

Theory of operation

Doc ID 10853 Rev 8

25/60

The tamper circuit works if the energies associated with the two current channels are both

positive or negative, if the two energies have different sign, the tamper is on all the time

however, the channel with the associated higher power is selected for the final computation

of energy.

In single wire mode, the apparent energy rather than the active is used for tamper detection.

When internal signals are not good enough to perform the calculations, i.e. line period is out

or range or

ΔΣ signals from analog section are stacked at high or low logic level, or no load

condition is activated, the tamper module is disabled and its state is preset to normal.

8.10.1

Detailed operational description

The meter is initially set to normal state, i.e. tamper not detected.In this condition the

primary channel is selected for final integration of energy. In such state the values of both

load currents should not differ more than the accuracy difference of the channels does.

Sixty-four periods of line voltage is used as a tamper checking period.

After 24 periods of line voltage two internal signals MUX and INH are changed in order to

enable secondary current channel and to freeze the last power and RMS values of primary

current channel. The following 16 periods of line frequency are used for tamper detection

integration. During this gap, the final energy calculation does not use the signal from

selected channel but the frozen values.

Four line periods after the INH switch, the integration of power from secondary current

channel is started and lasts four periods. Additional four line periods later MUX signal is

switched back to primary current channel and the integration for tamper detection is started.

The timings of MUX and INH signals are shown in Figure 18 below.

When the secondary channel is selected to be integrated by the final energy integrator, the

MUX and INH signals change according to Figure 19 below.

This means that energy of four periods from secondary channel followed by energy of four

periods from primary channel is sampled within the tamper module. From these two

Figure 18.

Timings of tamper module - Primary channel selected

MUX

Ch 1Ch 2Ch 1Ch 1

INH

Tamper power integrators

Cycles

Figure 19.

Timings of tamper module - Secondary channel selected

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