Dismantle single-phase rail energy meter detailed graphic analysis

The above several sheets are the structure of single-phase electric meter, the size is only 1P rail size. It can be seen that the meter has an accuracy class 1 active energy meter, double insulation protection, rated voltage 220VAC, frequency 50/60Hz, meter rated circuit Ib 5A maximum current. Imax 40A, pulse constant 3200imp / KWh, that is, 1 degree of electricity, the above pulse light flashes 3200 times. The communication method adopts the conventional RS485 of the electric meter. Terminals 1 and 2 are the incoming and outgoing lines of the live line, and the 3 and 4 terminals are the incoming and outgoing lines of the zero line. 47 and 48 are pulse output terminals used for calibration. 58 and 59 are RS485 communication terminals.
The side cover is connected by a snap and is opened with a screwdriver to see the circuit board inside. The circuit board inside is relatively simple.

Remove the circuit board and see the bottom circuit. You can see that the surface of the board is coated with a layer of three anti-paint. The first is the energy metering chip, the metering and sampling sharp energy micro-measurement chip RN8211, which is a SOC chip that integrates metering function, liquid crystal driver and MCU. It only needs one chip to complete the design of a table. At present, the electronic energy meter is basically It is in this way. Low cost and high reliability.

The voltage sampling uses four 1206 43K resistors and one 1206 1K resistor in series. The current sampling is sampled using the manganese copper resistor of the upper live line terminal, and the middle section of the terminal is manganese copper. The storage part is equipped with a Fujitsu ferroelectric memory, MB85RC16 size 16K, why not use EEPROM, mainly considering the service life, the data stored in the meter is frequently read and written.

The communication part RS485 chip uses Maxim's MAX487ESA industrial grade chip, and the chip that will use Maxim is also quite a local tyrant. In the protection of RS485 interface, it is also simple. The direct protection of port AB uses one TVS tube P065B1R03G, and the AB line is connected in series with 0603 10Ω protection resistor. I don't know what level of testing I can pass. The 485 voltage part is using a Jiangsu Changjiang Electronics Technology CJ78L05. After reading the bottom circuit, look at the top part of the circuit, the top is mainly the AC-DC part.
AC-DC uses PI's LNK562D chip, and the power supply uses a 431+ optocoupler feedback flyback power supply.

The input capacitor uses SAMON high voltage 2.2uF/400V electrolytic capacitor. The input part of the AC-DC power supply is basically unprotected. Only 1.5K resistors are connected in series on L and N. No EMI device is seen. It is estimated that considering the structure size, other protective devices should be added to the outside during actual use.

Summary: The overall result of the table is small in design and clever in structure. The main components use materials from large manufacturers, but the protection capability on the AC-DC and communication RS485 is relatively poor.