Datasheet

STPMC1 Theory of operation
Doc ID 15728 Rev 7 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
Register 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)
K
P
1000
C2
10
⋅
------ ----- ------
Wh[]=
K
P
1000
C2
10
⋅
------- ---- ------
Wh[]=
K
Q
1000
C2
10
⋅
-----------------
Varh[]=
K
Q
1000
C2
9
⋅
------- ---- ----
Varh[]=
K
F
1000
C2
10
⋅
------ ---- -------
Wh[]=
K
F
1000
C2
9
⋅
------ ---- -----
Wh[]=
K
R
1000
C2
10
⋅
------ ---- -------
Varh[]=
K
R
1000
C2
9
⋅
------ ---- -----
Varh[]=