STPM32_V02 datasheet(41/89 Pages) STMICROELECTRONICS

41 / 89 page

where TOL is selected according to Table 18.

Detection threshold is much higher than the accuracy difference of the current channels, which should be less

than 0.2%, but, some headroom should be left for possible transition effect, due to accidental synchronism of load

current change at the rate of energy sampling.

Tamper circuit works if energies associated with the two current channels are both positive or negative, if two

energies have different sign, a warning flag “TAMPER OR WRONG” in DSP_SR1 or DSP_SR2 is set.

The channel with higher energy is signaled by PHx TAMPER status bit in DSP_SR1 or DSP_SR2.

When internal signals are not good enough to perform the calculations, for example line period is out or range or

sigma-delta signals from analog section are stuck at high or low logic level, the tamper module is disabled and its

state is set to normal.

8.4.12

AH accumulation

In this particular tamper, the neutral wire is disconnected from the meter and the STPM3x does not sense the

voltage anymore, while it keeps sensing the current information. In these conditions, AH accumulator can be used

by the microcontroller to regularly calculate the billing based on a nominal voltage value due to the following

equation:

Equation 18

(18)

Energy = AH_ACC[31:0] · LSBAH_ACC · VNOM [Wh]

Figure 45. AH accumulation block

AH_ACC[31:0]

IRMS[17:0]

DCLK

The accumulation of current values is controlled by AH status bit. AH bit is set when PER_ERR = 1 and real

values of current overcome an upper threshold set in AH_UPx[11:0] in DSP_CR9 and DSP_CR11. This bit is

cleared when RMS current drops below AH_DOWNx[11:0] threshold in DSP_CR10 and DSP_CR12.

To stabilize the current accumulation, SAG event should be monitored by setting some thresholds in the related

STPM32, STPM33, STPM34

Functional description of hardwired DSP

DS10272 - Rev 13

page 41/89

STPM32 Datasheet(PDF) 41 Page - STMicroelectronics