STPM11 datasheet(37/45 Pages) STMICROELECTRONICS

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STPM11/12/13/14

STPM1x calibration

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STPM1x calibration

Energy meters based on STPM1x devices are calibrated on the frequency of the output

pulse signal.

The devices are comprised of two independent meter channels for line voltage and current

respectively. Each channel includes its own digital calibrator, to adjust the voltage and

current signals coming from the sensors in the range of ±12.5% in 256 steps. A digital filter

is included to remove any signal DC component.

The devices produce an energy output pulse signal whose frequency is proportional to the

measured active energy.

The devices have an embedded memory, 54 bits, used for configuration and calibration

purposes. The value of these bits can be written temporarily or permanently through CFGI

communication channel.

The basic information needed to start the calibration procedure is found in Table 16 and

Table 17:

The following typical STPM01 parameters and constants are also known:

Av is constant. While, Ai is chosen according to the sensor

Gv and Gi are constant

Cv and Ci are 8bits register (CHV, CHP and CHS)

From the values above and for both the given amplification factor and initial calibration data,

the following target values can be calculated:

Considering that Ci=0 generates a correction of 75% and that Ci=128 determines a

correction factor of 87.5%, and the same for Cv, the total correction for the power stands

within Kp = Kv*Ki = (0.75*0.75)=56.25% and 100%, and Cv=Ci=128 gives a correction

factor of Kp= (0.875*0.875) = 76.5625%

Table 16.

Calibration entries

Symbol

Description

Value

Line RMS voltage

(230 V)

Line RMS current

(5 A)

Power sensitivity

(LED: P=128000 pulses/kWh, Stepper Motor: PM=P/64= 2000 pulses/kWh)

Shunt Sensor

0,42 mv/A

Table 17.

Device calculation constants

Symbol

Description

Value

Vbg

Reference voltage

(1.23 V

± 2%)

Clock

(223 Hz

± 50ppm)

Av, Ai

Amplification of ADC

± 1%, (8, 16, 24, 32) ± 2%))

Gain of voltage and current decimation filters

(0.504008)

Cv, Ci

Calibration data range

(min = 0, ini = 128, max = 255)

AW Bit position that generates LED signal

(211)

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