DocID18304 Rev 1

5/38

AN3322

List of figures

List of figures

Figure 1.

Requirements for Class B power meter precision, three ranges . . . . . . . . . . . . . . . . . . . . . 7

Figure 2.

Template used to check meter accuracy (up to Imax) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 3.

Typical thermal noise present on STM32 meter platform. Histogram shows noise

equivalent to white Gaussian noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 4.

Internal and external analog input pin capacitors and resistors . . . . . . . . . . . . . . . . . . . . . 12

Figure 5.

Complete block diagram of the algorithm used in STM32 power meter . . . . . . . . . . . . . . . 13

Figure 6.

Voltage circuitry of STM32 meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 7.

Current circuitry of STM32 meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 8.

Current circuitry of STM32 meter, op amp saturation marked by red circle . . . . . . . . . . . . 16

Figure 9.

Figure 10.

Figure 11.

Instant power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 12.

Parasitic frequency FH in detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 13.

Error of URMS vs. the timer error in timer ticks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 14.

Error of URMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 15.

Finer calculation of zero crossing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 16.

Voltage signal crossing zero voltage line twice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 17.

Voltage signal used for correct zero crossing after proper filtering. . . . . . . . . . . . . . . . . . . 29

Figure 18.

Zero crossing for green - U, blue - ILG, red- IHG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 19.

Error of instant power for PF = 1 and PF = 0.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 20.

Error of instant power caused by phase shift for PF = 1. . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 21.

Error of instant power caused by phase shift for PF = 0.5 . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 22.

Analog part schematic - part 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 23.

Analog part schematic - part 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36