Slave-end intelligent electric energy meter and RS485 enabling automatic conversion circuit thereof
By using a combined circuit of the first optocoupler, switch tube and voltage division branch in the slave terminal smart power meter, the full range baud rate transmission and reception signal enable automatic conversion of the RS485 communication circuit is realized, which solves the communication failure problem in the prior art, meets industry standards and reduces power consumption.
Patent Information
- Application Number
- CN202510558100.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-29
- Publication Date
- 2025-08-15
AI Technical Summary
In the prior art, the RS485 communication circuit optocoupling isolation solution of the slave terminal smart power meter cannot meet the problem of automatic conversion of the full range of baud rate transmission and reception signal.
The combined circuit of the first optocouple, the first switching tube, the second switching tube and the voltage divider branch is adopted, and the control end of the switch tube is connected through the emitter on the secondary side of the optocouple, and combined with the voltage divider branch, the automatic conversion enabled by the transmitter and receiver of the RS485 chip is achieved, and the high and low electric frequency pulse width delay of the optical coupler output signal is shortened.
It effectively meets the RS485 communication baud rate requirements stipulated in the power meter industry standards, solves the problem that the optocoupler isolation solution cannot meet the automatic conversion of the full range of baud rate transmission and reception signals, reduces power consumption and simplifies the communication program code.
Smart Images
Figure CN120490590A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of smart meter communication, and in particular relates to a slave-end smart electric energy meter and an RS485-enabled automatic conversion circuit thereof. Background Art
[0002] As an energy metering device, the smart energy meter is equipped with a standard RS485 communication circuit. In the RS485 circuit, the RS485 transmitter enable and receiver enable circuits generally use the IO port of the energy meter MCU chip to enable the transmitter of the RS485 chip. The receiver enables DE to control, such as Figure 1 As shown, the IO port of the MCU chip is connected through the optocoupler O2 However, this circuit will occupy an IO port of the energy meter MCU and use an additional optocoupler for isolation (the energy meter standard requires RS485 to be isolated).
[0003] In order to solve the problem that the RS485 transmitter enable and receiver enable circuits occupy the IO port of the energy meter MCU, the transmitter enable circuit of the RS485 chip is generally used. The receiver enables a level switching circuit on the DE port, such as Figure 2 As shown in the figure, the level switching circuit includes transistors, capacitors and resistors. When the MCU's 485_TXD is high, the optocoupler O2 is cut off, the transistor Q1 is cut off, the collector of the transistor Q1 is low, and the RS485 chip transmitter is enabled. When the 485_TXD of the MCU is at a high level, the RS485 chip is in the sending state; when the 485_TXD of the MCU is at a low level, the optocoupler O2 is turned on, the transistor Q1 is turned on, and the transmitter of the RS485 chip is enabled. When 485_TXD is low and receiver enable DE is high, the RS485 chip is in the receiving state. Capacitor C2 is charged through resistor R9, causing the voltage on capacitor C2 to rise. When 485_TXD is high, optocoupler O2 is turned off, and transistor Q1 is turned off. At this time, capacitor C2 discharges through resistors R8 and R9, maintaining the RS485 chip receiver enable DE at a high level. The RS485 remains in the receiving state. The charging and discharging principle of capacitor C2 is used to maintain the RS485 receiver enable DE at a high level until the RS485 chip completes data reception and sends it to an external controller or meter reading terminal via the A / B bus. However, the electricity meter industry standard stipulates that the RS485 communication rate can be set between 1200bps and 115200bps. This circuit uses the capacitor discharge time and is not compatible with the full baud rate range of 1200bps to 115200bps. Summary of the Invention
[0004] The object of the present invention is to provide a slave-end smart energy meter and its RS485 enabling automatic conversion circuit, so as to solve the problem in the prior art that the RS485 communication circuit optocoupler isolation solution of the slave-end smart energy meter cannot meet the full range of baud rate transmission and reception signal enabling automatic conversion.
[0005] To solve the above technical problems, the present invention provides an RS485 enabling automatic conversion circuit for a slave-end smart electric energy meter, comprising a first optocoupler, a first switching tube, a second switching tube and a voltage divider branch; the primary side of the first optocoupler is used to be connected in series between a first power supply and a transmitting end of a main control chip of the electric energy meter, and the emitter of the secondary side of the first optocoupler is connected to the control end of the first switching tube; the input end and the output end of the first switching tube, as well as the voltage divider branch, are all connected in series between the second power supply and ground, the voltage dividing point of the voltage divider branch is connected to the control end of the second switching tube, the input end and the output end of the second switching tube are connected in series between a third power supply and ground, and the output end of the second switching tube is used to connect to the two enable ends of the RS485 chip.
[0006] Furthermore, the emitter of the secondary side of the first optocoupler is connected to the control end of the first switch tube through a first resistor and a first capacitor arranged in parallel, and both ends of the first resistor are grounded through a second resistor and a third resistor respectively.
[0007] Furthermore, the series connection point between the voltage dividing branch and the first switch tube is used to connect to the driving input end of the RS485 chip.
[0008] Furthermore, the first switching tube is an NPN type transistor, the base of the NPN type transistor is the control end of the first switching tube, and the collector and emitter of the NPN type transistor are the input end and output end of the first switching tube; the second switching tube is a PNP type transistor, and the emitter and collector of the PNP type transistor are the input end and output end of the second switching tube.
[0009] To solve the above technical problems, the present invention also provides a slave-end smart electricity meter, comprising a main control chip and an RS485 chip, and also comprising a first optocoupler, a first switch tube, a second switch tube and a voltage divider branch; the primary side of the first optocoupler is connected in series between the first power supply and the transmitting end of the main control chip of the electricity meter, and the emitter of the secondary side of the first optocoupler is connected to the control end of the first switch tube; the input end and the output end of the first switch tube, and the voltage divider branch are all connected in series between the second power supply and the ground, the voltage divider point of the voltage divider branch is connected to the control end of the second switch tube, the input end and the output end of the second switch tube are connected in series between the third power supply and the ground, and the output end of the second switch tube is connected to the two enable ends of the RS485 chip.
[0010] Furthermore, the emitter of the secondary side of the first optocoupler is connected to the control end of the first switch tube through a first resistor and a first capacitor arranged in parallel, and both ends of the first resistor are grounded through a second resistor and a third resistor respectively.
[0011] Furthermore, a connection point between the voltage dividing branch and the first switch tube is connected to a driving input terminal of the RS485 chip.
[0012] Furthermore, the first switching tube is an NPN type transistor, the base of the NPN type transistor is the control end of the first switching tube, and the collector and emitter of the NPN type transistor are the input end and output end of the first switching tube; the second switching tube is a PNP type transistor, and the emitter and collector of the PNP type transistor are the input end and output end of the second switching tube.
[0013] Furthermore, the A terminal of the RS485 chip is connected to the second power supply through a pull-up resistor, and the B terminal of the RS485 chip is grounded through a pull-down resistor.
[0014] Furthermore, a connection point between the pull-up resistor and the second power supply is grounded via a filter capacitor.
[0015] Its beneficial effects are as follows: the present invention is an improved invention, which provides an RS485 automatic conversion enabling circuit for a slave-end smart meter. In addition to a first optocoupler, the circuit is also provided with a first switch tube and a second switch tube between the main control chip and the RS485 chip, so that the level signal output by the first optocoupler is input to the RS485 chip through the switch tube (which needs to be coordinated with a voltage divider circuit), effectively shortening the high and low frequency pulse width delays of the first optocoupler signal waveform, and avoiding the situation where communication failure occurs when the signal output by the optocoupler is directly input to the RS485 chip due to the high and low level delays of the optocoupler output exceeding the standard pulse width signal, meeting the RS485 communication baud rate requirements specified by the electric energy meter industry standard, and solving the problem in the prior art that the optocoupler isolation solution of the RS485 communication circuit of the slave-end smart electric energy meter cannot meet the full range of baud rate transmission and reception signal enabling automatic conversion. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 This is a circuit diagram of an IO port control enable circuit of an electric energy meter MCU chip in the prior art solution;
[0017] Figure 2 This is a prior art solution that enables switching circuit diagrams through the C2 charge and discharge circuit;
[0018] Figure 3 The present invention discloses an RS485 automatic conversion enabling circuit diagram. DETAILED DESCRIPTION
[0019] The present invention discloses an RS485 automatic enable conversion circuit for a slave-side smart energy meter, comprising: a first optocoupler, a first switch tube, a second switch tube, and a voltage divider branch. The transmitter enable and receiver enable automatic conversion circuit of the RS485 chip meets the requirement for automatic enable conversion of full-range baud rate receiving and transmitting signals. The first optocoupler, the first switch tube, the second switch tube, and the voltage divider branch are connected in a manner that: the primary side of the first optocoupler is connected in series between a first power supply and the transmitting end of the main control chip, and the emitter of the secondary side of the first optocoupler is connected to the control end of the first switch tube; the voltage divider branch and the first switch tube are connected in series between a second power supply and ground, the voltage divider point of the voltage divider branch is connected to the control end of the second switch tube, the input and output ends of the second switch tube are connected in series between a third power supply and ground, and the output end of the second switch tube is connected to the two enable ends of the RS485 chip. The communication circuit of the RS485 automatic enable conversion circuit of the slave-side smart energy meter of the present invention is more concise and efficient, and can meet the RS485 communication rate requirements specified by the energy meter industry standard.
[0020] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.
[0021] An embodiment of a slave-side smart electric energy meter:
[0022] The embodiment of the present invention provides a slave-end smart energy meter, which is connected to the master-end smart terminal for communication. Figure 3As shown, the slave-end smart energy meter includes an energy meter MCU chip (i.e., a main control chip), an RS485 chip U1, an optocoupler O2 (i.e., a first optocoupler), an optocoupler O1 (i.e., a second optocoupler), a third switch tube Q1, a first switch tube Q2, a second switch tube Q3, and a voltage divider branch; wherein the first switch tube, the second switch tube, and the third switch tube have a control terminal, an input terminal, and an output terminal, the input terminal and the output terminal being connected in series in the loop where the switch tube is located, and the control terminal can be used to control the on / off state of the switch tube. In this embodiment, the first switch tube Q2, the second switch tube Q3, and the third switch tube Q1 are all triodes, and the triodes Q1 and Q2 are both NPN-type triodes, and the triode Q3 is a PNP-type triode. The bases of the triodes Q1, Q2, and Q3 are the control terminals of the switches, the collectors and emitters of the triodes Q1 and Q2 are the input terminals and output terminals of the switches, respectively, and the emitter and collector of the triode Q3 are the input terminals and output terminals of the switches, respectively. As other implementation methods, other types of switch tubes can be selected according to actual needs, such as field effect tubes FET, insulated gate bipolar transistors IGBT, etc. When other types of switch tubes are selected, the corresponding input end, output end, and control end are respectively: if it is a P-channel FET, its gate is the control end of the switch tube, and the source and drain are the input end and output end of the switch tube respectively; if it is an N-channel FET, its gate is the control end of the switch tube, and the drain and source are the input end and output end of the switch tube respectively. The host-side intelligent terminal includes an RS485 chip U2, and the slave-side intelligent energy meter and the host-side intelligent terminal are connected through their respective RS485 chips. The specific connection relationship circuit is as follows: Figure 3 As shown, the details are as follows:
[0023] The primary side of the optocoupler O2 is connected in series between the power supply VDD (i.e., the first power supply) and the transmitter TXD of the energy meter MCU chip, and a resistor R14 is also connected in series on the connection line between the primary side cathode of the optocoupler O2 and the transmitter TXD of the energy meter MCU chip. The emitter of the secondary side of the optocoupler O2 is connected to the base of the transistor Q2, and the connection line between the emitter of the secondary side of the optocoupler O2 and the base of the transistor Q2 is also connected in series with a resistor R17 (i.e., the first resistor) and a capacitor C6 (i.e., the first capacitor) arranged in parallel. The two ends of the resistor R17 are respectively connected to ground through R15 (i.e., the second resistor) and R31 (i.e., the third resistor). The voltage divider branch is composed of resistors R2 and R3 in series. The voltage divider branch and the transistor Q2 are connected in series between the power supply VDD485 (i.e., the second power supply) and ground. The voltage divider point of the voltage divider branch is connected to the base of the transistor Q3, and the collector of the transistor Q2 is connected to the DI terminal (the drive input terminal) of the RS485 chip. The emitter of transistor Q3 is connected to VDD485 (i.e. the third power supply), and the collector of transistor Q3 is connected to the enable terminal of RS485 chip U1. The connection point between the collector of the transistor Q3 and the enable terminal of the RS485 chip U1 is grounded through the resistor R9.
[0024] The primary side of the optocoupler O1 is connected in series between the power supply VDD485 and the RO terminal (receiving output terminal) of the RS485 chip U1, and a resistor R10 is also connected in series on the connection line between the primary side cathode of the optocoupler O1 and the RO terminal of the RS485 chip U1; the emitter of the secondary side of the optocoupler O1 is connected to the base of the transistor Q1, the transistor Q1 is connected in series between the power supply VDD and the ground, and the collector of the transistor Q1 is connected to the receiving terminal RXD of the electric energy meter MCU chip, and the connection point between the collector of the transistor Q1 and the receiving terminal RXD of the electric energy meter MCU chip is connected to the power supply VDD through the resistor R1; the connection line between the emitter of the secondary side of the optocoupler O1 and the base of the transistor Q1 is also connected to a resistor R4 (i.e., the fourth resistor) and a capacitor C2 (i.e., the second capacitor) arranged in parallel, and the two ends of the resistor R4 are grounded through a resistor R7 (i.e., the fifth resistor) and a resistor R8 (i.e., the sixth resistor), respectively.
[0025] Terminal A of RS485 chip U1 is connected to power supply VDD485 via resistor R11 (i.e., a pull-up resistor). Terminal B of RS485 chip U1 is grounded via resistor R32 (i.e., a pull-down resistor). The connection point between resistor R11 in series with terminal A of RS485 chip U1 and power supply VDD485 is grounded via capacitor C5 (i.e., a third capacitor). Terminal A of RS485 chip U1 is connected to terminal A of host-side RS485 chip U2, and a thermistor RT2 is provided on the connection line. Terminal B of RS485 chip U1 is connected to terminal B of host-side RS485 chip U2, and a thermistor RT1 is provided on the connection line. A TVS diode is provided between terminals A and B, between terminal A and ground, and between terminal B and ground. These diodes are TVS2, TVS3, and TVS1, respectively. TSS diodes can also be provided. Among them, the function of the pull-up and pull-down resistors connected to the A / B terminals is to limit the current, preventing sudden external overvoltage and overcurrent interference from being introduced into the A / B terminals, causing damage to the A / B terminals; the function of the thermistor and TVS tube (or TSS tube) is to limit the current and provide overvoltage clamping protection.
[0026] It should be noted that the optocoupler in this circuit is an ordinary optocoupler. At a communication rate of 115200bps, the delay of a high level or low level in the waveform of an ordinary optocoupler is more than 10μs (the effective level becomes narrower and cannot be identified). At a communication rate of 115200bps, the standard pulse width of a high level or low level is 8.68μs (1 / 115200). Therefore, when the ordinary optocoupler is directly input to the MCU or 485 chip, the delay of a high level or low level exceeds the standard pulse width signal. At this time, there is no high or low level change, and the change cannot be effectively identified, resulting in communication failure. Therefore, in this circuit, a third switch tube Q1 is added to the secondary side of the optocoupler O1, and a first switch tube Q2 is added to the secondary side of the optocoupler O2 to meet the requirements of automatic conversion of full-range baud rate transceiver signals.
[0027] The third switch Q1 (transistor Q1), capacitor C2, resistors R4, R7, and R8 act as an acceleration circuit, accelerating the high and low pulse widths of the optocoupler waveform from over 10μs to under 0-2μs, thereby meeting the 115200bps communication requirement. The specific principle is as follows: when the RS485 chip's RO terminal sends a low level, the optocoupler O1 turns on. At this time, the secondary side of the optocoupler O1 turns on, instantly charging capacitor C2. This current also flows into the base of the transistor Q1, causing Q1 to turn on quickly. Q1's collector outputs a low level, which is then fed into the MCU. When RO sends a high level, the optocoupler O1 turns off, discharging capacitor C2. The negative voltage on the left side of capacitor C2 instantly pulls the hole pairs in the PN junction between the base and emitter of the transistor Q1 to the capacitor side, quickly turning off the transistor Q1. At this time, the collector of Q1 is quickly pulled up to a high level, which is fed into the MCU's IO port. After actual testing, the pulse width delay can be controlled within 2μs, and normal communication can be achieved. The working principle of the first switch tube Q2 (ie, transistor Q2), capacitor C6, resistor R17, resistor R15, and resistor R31 is consistent with the above principle.
[0028] The specific working process of the slave-side smart energy meter includes:
[0029] (1) When the RS485 chip U1 is in the waiting state (that is, the RS485 chip U1 can send information but there is no external meter reading signal at this time, is high), the transmitting end TXD is high, the optocoupler O2 is cut off, the collector of the transistor Q3 is low, and the transmitter of the RS485 chip U1 is enabled. It is high level, at this time RS485 chip U1 is in sending state; after A and B buses send meter reading data to RS485 chip U1, the signal is transmitted to the energy meter MCU chip through RO.
[0030] (2) After the electric energy meter MCU chip receives the external meter reading data, it processes the data and sends the data to the optocoupler O2 through the transmitter TXD. At this time, the transmitter TXD sends a low level, the optocoupler O2 is turned on, the transistor Q2 is turned on, and the transistor Q3 is turned on. At this time, the collector voltage of the transistor Q3 is high, the RS485 chip U1 receiver enable DE is high, the RS485 chip U1 is in the receiving state, receives low-level data, and then sends the low-level data to the A / B bus.
[0031] (3) When the transmitter TXD sends a high level, the optocoupler O2, transistors Q2, Q3 are cut off, and the RS485 chip U1 receiver enable DE is low, and the transmitter is enabled It is high level. At this time, the RS485 chip U1 is in the transmitter enable state and the receive enable has been turned off. However, due to the host-side equipment industry standard requiring the RS458 chip circuit A bus to be configured with a pull-up resistor and the B bus to be configured with a pull-down resistor, the voltage difference between the A / B bus ends is still high level. The host end can still sample the complete high and low level signals sent by the RS485 chip U1 of the energy meter, and can still meet the normal RS485 meter reading communication needs.
[0032] According to the embodiment of the present invention, when the transmitting end TXD sends a low level, the RS485 chip U1 on the slave end (electricity meter) sends a low level to the A / B bus; when the transmitting end TXD sends a high level, the level on the A / B bus of the RS485 chip U1 on the slave end (electricity meter) outputs a high level through the voltage difference between the pull-up and pull-down resistors on the host end. The host end can still normally sample the complete high and low level signals sent by the RS485 chip U1 on the slave end electric energy meter, and can still meet the normal RS485 meter reading communication requirements. Therefore, the RS485 chip U1 on the slave end electric energy meter of the embodiment of the present invention only needs to send a low level signal to achieve automatic enable conversion of the RS485 communication baud rate from 1200bps to 115200bps. The power consumption of the conversion circuit is reduced by 50% and the program code of the RS485 communication is further simplified.
[0033] An RS485-enabled automatic conversion circuit embodiment of a slave-side smart electric energy meter:
[0034] An RS485 enabled automatic conversion circuit embodiment of a slave-side smart electric energy meter of the present invention specifically includes a first optical coupler, a first switch tube, a second switch tube and a voltage divider branch, and the circuit connection relationship is as follows Figure 3 As shown, the first optocoupler is O2, the first switching tube is specifically a transistor Q2, the second switching tube is specifically a transistor Q3, and the voltage divider branch includes resistors R2 and R3 connected in series. The primary side of the optocoupler O2 is used to be connected in series between the first power supply VDD and the transmitting terminal TXD of the energy meter main control chip MCU, and the emitter of the secondary side of the optocoupler O2 is connected to the control terminal of the first switching tube (specifically, the base of the transistor Q2); the input and output ends of the first switching tube and the voltage divider branch are all connected in series between the second power supply and ground, and the voltage divider point of the voltage divider branch is connected to the control terminal of the second switching tube (specifically, the base of the transistor Q3). The input and output ends of the second switching tube are connected in series between the third power supply and ground, and the output end of the second switching tube is used to connect to the two enable terminals of the RS485 chip.
[0035] The specific circuit structure, connection relationship, working process and principle of the circuit have been described in detail in an embodiment of a slave-end smart electric energy meter, and will not be repeated in this embodiment.
Claims
1. An RS485 enabled automatic conversion circuit for a slave-side smart electric energy meter, characterized in that: It includes a first optocoupler, a first switching tube, a second switching tube and a voltage divider branch; the primary side of the first optocoupler is used to be connected in series between the first power supply and the transmitting end of the electric energy meter main control chip, and the emitter of the secondary side of the first optocoupler is connected to the control end of the first switching tube; the input end and output end of the first switching tube and the voltage divider branch are all connected in series between the second power supply and ground, the voltage dividing point of the voltage divider branch is connected to the control end of the second switching tube, the input end and output end of the second switching tube are connected in series between the third power supply and ground, and the output end of the second switching tube is used to connect to the two enable ends of the RS485 chip.
2. The RS485-enabled automatic conversion circuit of the slave-side smart electric energy meter according to claim 1, characterized in that: The emitter of the secondary side of the first optocoupler is connected to the control end of the first switch tube through a first resistor and a first capacitor arranged in parallel, and both ends of the first resistor are grounded through a second resistor and a third resistor respectively.
3. The RS485-enabled automatic conversion circuit of the slave-side smart electric energy meter according to claim 1, characterized in that: The serial connection point between the voltage dividing branch and the first switch tube is used to connect to the driving input end of the RS485 chip.
4. The RS485-enabled automatic conversion circuit of the slave-side smart electric energy meter according to any one of claims 1 to 3, characterized in that: The first switching tube is an NPN type transistor, the base of the NPN type transistor is the control end of the first switching tube, and the collector and emitter of the NPN type transistor are the input end and output end of the first switching tube; the second switching tube is a PNP type transistor, and the emitter and collector of the PNP type transistor are the input end and output end of the second switching tube.
5. A slave-end smart energy meter, comprising a main control chip and an RS485 chip, characterized in that: It also includes a first optocoupler, a first switching tube, a second switching tube and a voltage divider branch; the primary side of the first optocoupler is connected in series between the first power supply and the transmitting end of the electric energy meter main control chip, and the emitter of the secondary side of the first optocoupler is connected to the control end of the first switching tube; the input end and the output end of the first switching tube, and the voltage divider branch are all connected in series between the second power supply and the ground, the voltage dividing point of the voltage divider branch is connected to the control end of the second switching tube, the input end and the output end of the second switching tube are connected in series between the third power supply and the ground, and the output end of the second switching tube is connected to the two enable ends of the RS485 chip.
6. The slave-end smart electric energy meter according to claim 5, characterized in that: The emitter of the secondary side of the first optocoupler is connected to the control end of the first switch tube through a first resistor and a first capacitor arranged in parallel, and both ends of the first resistor are grounded through a second resistor and a third resistor respectively.
7. The slave-end smart electric energy meter according to claim 5, characterized in that: The series connection point between the voltage dividing branch and the first switch tube is connected to the driving input end of the RS485 chip.
8. The slave-end smart electric energy meter according to any one of claims 5 to 7, characterized in that: The first switching tube is an NPN type transistor, the base of the NPN type transistor is the control end of the first switching tube, and the collector and emitter of the NPN type transistor are the input end and output end of the first switching tube; the second switching tube is a PNP type transistor, and the emitter and collector of the PNP type transistor are the input end and output end of the second switching tube.
9. The slave-end smart electric energy meter according to any one of claims 5 to 7, characterized in that: The A terminal of the RS485 chip is connected to the second power supply through a pull-up resistor, and the B terminal of the RS485 chip is grounded through a pull-down resistor.
10. The slave-end smart electric energy meter according to claim 9, characterized in that: The connection point between the pull-up resistor and the second power supply is grounded via a filter capacitor.