STPM01_11 datasheet(21/60 Pages) STMICROELECTRONICS

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STPM01

Theory of operation

Doc ID 10853 Rev 8

21/60

The BFR flag is also set if the register value of the RMS voltage drops below 64. BFR is

cleared when the register value goes above 128. The BFR, then, also gives information

about the presence of the line voltage within the meter.

When the BFR error is set, the computation of power is zero unless the FRS bit is set or the

single wire mode operation is selected (see Section 8.6).

In fact, the effect of the BFR bit can be overridden by setting FRS configuration bit.

It means that if FRS is set and BFR is also set, all the energy computation is carried on as

BFR was cleared. In this case then p=u*i, where u could be zero or not (if BFR was set

because voltage RMS register value is below 64).

In standalone mode, the MOP, MON and LED provide the energy information, their

operation is not affected by FRS bit, it means that when BFR is set they stop switching

regardless the FRS value.

8.6

Single wire meter mode (only Rogowsky coil sensor)

STPM01 support single wire meter (SWM) operation when working with Rogowsky coil

current sensors. In SWM mode there is no available voltage information in the voltage

channel. It is possible that someone has disconnected one wire (live or neutral) of the meter

Figure 16.

LIN and BFR signal

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