1. http://www.analog.com/energymeter Designing a EMC Compatible Electronic Meter using AD7755 a

2. http://www.analog.com/energymeter Design For Immunity to Electromagnetic Disturbances "the meter shall be designed in such a way that conducted or radiated electromagnetic disturbances as well as electrostatic discharge do not damage nor substantially influence the meter” -Section 4.5 IEC1036

3. http://www.analog.com/energymeter What is EMC? Source-Path-Receptor Model EMC Stands for Electro-Magnetic Compatibility. The interference generated by the movement of electrons will travel through a path and result in the energy meter. Movement of Electrons RECEPTOR Energy Meter SOURCEPATH Common coupling effects: Frequency less than 30MHz (e.g. EFT) – Conduction Frequency between 30MHz to 300 MHz (e.g. RFI) – Cable Radiation Frequency larger than 300MHz (e.g. ESD, RFI) - Radiation

4. http://www.analog.com/energymeter EMC Requirement on IEC1036 IEC1036 specifies that the energy meter must be able to withstand: Electrostatic Discharge (ESD) up to 8kV Radio Frequency Interference (RFI) up to 10V/m near field Electrical Fast Transient and Surge (EFT) up to 4kV The AD7755, core of the energy meter, offers some protection against the above interferences. However, the energy meter circuit and PCB layout should be designed to divert the interference away from the AD7755 to ensure the expected lifespan of the energy meter is not affected. The AD7755 has passed 60 years life test

5. http://www.analog.com/energymeter ADE775x Family Architecture High Resolution Data Conversion Fixed Function DSP 101011... 111001... D.C. to 5KHz 16 bit ADC 16 bit ADC 16 bit ADC 16 bit ADC Multiply & LPF Digital-To- Frequency Serial Port Interface

6. http://www.analog.com/energymeter EMC Certified Electronic Energy Meter based on AD7755 The fixed function DSP in the AD7755 is highly effective against radiated EMC disturbances, however, external protection is essential to minimize the noise coupling through conduction. a AD7755

7. http://www.analog.com/energymeter Implementation: PCB Layout

8. http://www.analog.com/energymeter PCB Layout Layout considerations - Analog Performance Separate grounds were used to isolate the AD7755 and low level analog signals from the rest of the design Ground plane should be made as large as possible to keep the common ground impedance to a minimum Care was taken with the routing of the ground return current from the capacitor based PSU.

9. http://www.analog.com/energymeter PCB Layout Ground Plane helps reduce the impedance of the current path in an ESD/EFT event and reduce interference picks up through radiation.

10. http://www.analog.com/energymeter PCB Layout Layout considerations - EMC Separate grounds were used to isolate the AD7755 from electromagnetic disturbances. Power and ground connections are made through ferrite bead.

11. http://www.analog.com/energymeter PCB Layout: Some key areas Large digital/power supply ground plane (noisy) Ground shielding helps separate strong voltage signal from affecting weak current signal Weak differential signal lines are shielded by ground fill and are parallel and closed to each other Large analog ground plane (quiet)

12. http://www.analog.com/energymeter Implementation: Circuit Design

13. http://www.analog.com/energymeter Inductance of the Shunt Shunt inductance can create a high impedance path at high frequency: ESD/EFT and RFI picked up through the cable will travel to the AD7755’s signal inputs V1P and V1N. Protection is needed!

14. http://www.analog.com/energymeter Design For Immunity to Electromagnetic Disturbances ESD (IEC1000-4- 2) Ferrite RC Filter R > 1kW Attenuation network R > 1MW EMI Filter on PSU Passed 25kV Contact discharge Specification requires for 8kV

15. http://www.analog.com/energymeter Design For Immunity to Electromagnetic Disturbances EFT (IEC1000-4-4) Ferrite & RC slows down edge. EFT appears as CM signal Ferrite & C slows down edge. MOV suppresses large differential EFT PCB layout isolates AD7755 from EFT in the signal ground Passed 5kV @ 15kHz Specification requires for 4kV @ 5kHz

16. http://www.analog.com/energymeter Design For Immunity to Electromagnetic Disturbances HF Field (IEC1000-4-3) EMI Filter on PSU shunting cap acts as bypass for RF Ferrite & RC make up effective HF filter PCB layout/grounding Passed 20V/m near field Specification calls for 10V/m

17. http://www.analog.com/energymeter Conclusion Good EMC design is essential to help ensure the lifespan and accuracy of a solid-state energy meter. Large ground plane, short analog signal lines help greatly reduce EMC problems. Components’ parasitic characteristics will usually dominant in a EMC situation. EMC Protection does not have to come with additional cost to a meter if the right component is used. For example, RC used in anti-aliasing filter can be effective EMC filter. Mechanical meter is also susceptible to EMC issues.

18. http://www.analog.com/energymeter EMC Can Be Achieved with Care in Circuit Design and Layout Emissions Immunity