STPM01 datasheet(50/60 Pages) STMICROELECTRONICS

50 / 60 page

STPM01 calibration

STPM01

50/60

Doc ID 10853 Rev 8

STPM01 calibration

Energy meters based on STPM01 device are calibrated in a fast and easy way. The

calibration is essentially based on the single calibration of the voltage and current channel

considering their RMS values rather than on the frequency of output pulse signal. When the

two channel are calibrated all the other measurement are calibrated too. This allows the

calibration to be performed in only one point shortening the production time of the meter.

This procedure is possible due to the below key points:

– Device is compound of two independent meter channels for line voltage and current

respectively. Each channel includes its own digital calibrator, to adjust the RMS in the

range of ±12.5 % in 256 steps, and digital filter, to remove any signal DC component.

All final results are not subject to calibration procedure because they are achieved

from such corrected signals by mathematical modules implemented by hardwired

DSP.

– Device computes different kind of energies: active, reactive and apparent. The active

energy is produced without 2nd harmonic of line frequency. It also computes RMS

values of measured voltage and current.

– Device produces an energy output pulse signal but information can also be read

through serial port interface, SPI, and communication channel.

– Device has an embedded memory, 56 bits, used for configuration and calibration

purposes. The value of these bits can be read or they can be changed temporarily or

permanently through SPI communication channel.

Let’s consider the basic information needed to start the calibration procedure:

The following typical STPM01 parameters and constants are also known:

Table 18.

Working point settings

Line RMS voltage

(230V)

Line RMS current

(5A)

Power sensitivity

(LED: P=128000 pulses/kWh, stepper motor: PM=P/64= 2000 pulses/kWh)

Shunt sensor

0,42 mv/A

Table 19.

Device constants

Parameter

Value

Tolerance

Internal reference voltage

VBG

1.23 V

± 2%

Internal calculation frequency

223 Hz

± 50 ppm

Amplification of voltage ADC

4± 1%

Amplification of current ADC

8, 16, 24, 32

± 2%

Gain of differentiator

GDIF

0,6135

Gain of integrator

GINT

0,815

Gain of decimation filter

GDF

1.004

RMS voltage register length

211

RMS current register length

216

Constant

DUD

217

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