STPMC1 datasheet(33/77 Pages) STMICROELECTRONICS

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STPMC1

Theory of operation

Doc ID 15728 Rev 6

33/77

EMI tamper condition is not available as internal status signal, but it is available (in OR with

other tamper conditions) on the SDATD pin of the device.

In peripheral application mode it is possible to detect EMI tamper comparing the value of the

16-bit DCuN and of the 12-bit RMSuN to the threshold through a microcontroller.

9.11

Energy to frequency conversion (configuration bits: APL,

KMOT, LVS, FUND)

The STPMC1 provides energy to frequency conversion both for calibration and energy

readout purposes.

The three hard-wired xDSP, implemented as four 2-channel

ΔΣ signal processors perform all

calculations and produce output data and signals. Inside them, each three stage decimation

filter inputs a filtered

ΔΣ signal and its integral as parallel bus or stream to the power and

RMS computer. All three streams of power (active, reactive and active from the fundamental

harmonic) are connected to the corresponding integrators.

Within the integrators, all three powers are accumulated into energies of 20-bit values

according to configuration bit ABS and the results are converted into pulse train signals, the

frequency of which is proportional to the accumulated energies. Each of these signals can

be brought out to the LED pin.

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.

Through calibration the meter is configured to provide a certain number of pulses per kWh

(referred to as power meter constant C) on the LED pin. According to the APL, KMOT, LVS

and FUND configuration bits, the frequency of LED signal can provide different information,

as shown in paragraphs

9.12 and 9.13.

Given C, the number of pulses per kWh provided, the relationship between the LSB value of

the source energy registers and the number of pulses provided to LED pin is indicated in the

table below:

Table 17.

Energy registers LSB value

SYS = 0, 1, 2, 4, 5, 6, 7

SYS = 3

3-ph active energy wide band (P)

3-ph reactive energy wide band (Q)

3-ph active energy fundamental (F)

3-ph reactive energy fundamental (R)

1000

⋅

----------------- Wh

[]

1000

⋅

----------------- Wh

[]

1000

⋅

----------------- Varh

[]

1000

⋅

--------------- Varh

[]

1000

⋅

----------------- Wh

[]

1000

⋅

--------------- Wh

[]

1000

⋅

----------------- Varh

[]

1000

⋅

--------------- Varh

[]

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