STPM10 datasheet(25/51 Pages) STMICROELECTRONICS

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STPM10

Theory of operation

Doc ID 17728 Rev 3

25/51

taken from the 11th bit of the active energy register, and consequently a relationship

between the LSB value of the active energy register and the number of pulses provided per

each kWh (P) can be defined as:

Equation 2

Due to the innovative and proprietary power calculation algorithm, the frequency signal is

not affected by any ripple at twice the line frequency. This feature strongly reduces the

calibration time of the meter.

In a practical example where the desired P is 64000 pulses/kWh (=17.7 Hz*kW), we have:

Equation 3

kAW=7.63*10-6 Wh

This means that the reading of 0x00001 in the active energy register represents 7.63 µWh,

while 0xFFFFF represents 8 Wh.

The LED pin can be driven from AW (active energy wide band), AF (active energy limited at

fundamental), RW (reactive energy) or SW (apparent energy) according to the value of the

KMOT bit.

In this case, since the LED pin is driven by signals different from that of AW, some other

relationship between the LSB of the register and the number of pulses per kWh provided by

the meter (P) must be defined:

Equation 4

kAF = 4*kAW [Wh]

kRW = 2*kAW [VARh]

kSW = kAW [VAh]

Table 9.

LED pin configuration

KMOT (2 bits)

Signal available on LED pin

# of pulses

AW Type0*

P [kWh]

AF Type1*

P [kWh]

P [kVARh]

P [kVAh]

[]

1000

⋅

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