STPM33 datasheet(58/89 Pages) STMICROELECTRONICS

58 / 89 page

Figure 53. Phase shift error

Voltage

Current capacitive

Current inductive

The θ angle can be measured through the error on active power (from LED) averaged over a certain number of

samples (for example 50) at power factor PF = 0,5.

For example, if the error = e, the phase shift between voltage and current is:

Equation 28

θ=arccos 1+e2 −60°

(28)

To compensate this error, PHC and PHV bits must be set as below, to introduce a correction factor φ = -θ.

Table 39. Phase compensation

Parameter

Value

φ≥0

PHVx=0x0

PHCx= φ∙SCLK

360∙fline

−flineSCLK∙29∙360°≤φ<0

PHVx=0x1

PHCx9 =0

PHCx8:0 =PHVx∙29+ φ∙SCLK

360∙fline

−flineSCLK∙210∙360°≤φ<−flineSCLK∙29∙360°

PHVx=0x2

PHCx9 =0x0

PHCx8:0 =PHVx∙210+ φ∙SCLK

360∙fline

−flineSCLK∙29∙3∙360°≤φ<−flineSCLK∙210∙360°

PHVx=0x3

PHCx9 =0x0

PHCx8:0 =PHVx∙29+ φ∙SCLK

360∙fline

9.2.3

Power offset calibration (OFAx, OFAFx, OFRx, OFSx bits)

The device has the power offset compensation register for all measured powers (active, active fundamental,

reactive and apparent) to compensate, for each channel, the power measured due to noise capture in the

application.

Power registers are signed values, (MSB is the sign and negative values are two's complemented); the power

offset registers are also signed registers with LSB value equal to 4 times the power LSB:

STPM32, STPM33, STPM34

Application calibration

DS10272 - Rev 13

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