A meter box opening detection circuit

Abstract

A meter box opening detection circuit includes: the positive electrode of the second diode D2 is connected to GND, the negative electrode thereof is connected to the signal input terminal IN and the first capacitor C1, and the other end of the first capacitor C1 is connected to the positive electrode A of the detection terminal; the collector of the transistor Q1 is connected to the signal output terminal OUT and the first resistor R1, and the emitter of the transistor Q1 is connected to GND; the negative electrode of the first diode D1 is connected to the base of the transistor Q1, and the positive electrode is connected to GND; the third capacitor C3 is connected in parallel with the second diode D2; one end of the second capacitor C2 is connected to the negative electrode of the first diode D1, and the other end thereof is connected to the negative electrode B of the detection terminal. The advantages are: using Y capacitor isolation, utilizing the characteristics of capacitors that can conduct AC signals, no external battery is required, no special meter box design is required, and at the same time, it can ensure that the detection function is still available when the external 220V AC power is cut off.

Description

Technical Field

[0001] The invention belongs to the technical field of power grid equipment, and in particular relates to a meter box opening detection circuit. Background Art

[0002] After years of reform and development of the State Grid, as well as technological improvements in electricity meters, opening the meter cover to steal electricity will inevitably require destroying the lead seal and the meter case. It is now difficult to steal electricity without being discovered on site. Although it is rare to steal electricity by opening the meter cover, there are still ways to steal electricity by opening the meter box to rewire, add jumpers, etc. During actual on-site operation of the electricity meter, there are only meter cover opening detection and terminal cover opening detection functions, but no meter box opening detection function. At the same time, the meter box lock is easy to be opened, which poses a risk of electricity theft.

[0003] The current detection method for opening the meter box is to refer to the design of the domestic concentrator remote signal circuit, through optocoupler isolation, and the optocoupler diode side relies on the 485 circuit isolation system main system main power supply V485 for power supply. When the meter box is opened, the remote signal terminal and MGND are disconnected, the optocoupler is not turned on, and the remote signal detection output is high level; when the meter box is closed, the remote signal terminal and MGND are short-circuited, the optocoupler is turned on, and the remote signal detection output is low level. However, this method has the following disadvantages: when the external 220V AC power is cut off, V485 will also lose power, and it cannot rely on the internal lithium battery for power supply detection.

[0004] Another method is to use optocoupler isolation, and the optocoupler diode side relies on an external battery for power supply. When the meter box is opened, the detection terminal and the negative pole of the battery are disconnected, the optocoupler is not turned on, and the meter box detection output is high; when the meter box is closed, the detection terminal and the negative pole of the battery are short-circuited, the optocoupler is turned on, and the meter box detection output is low. However, this method has the following disadvantages: first, the external battery is added, which increases the cost and requires a specially designed meter box to place the external battery; second, whether the external battery has power cannot be automatically determined and requires manual measurement. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a meter box opening detection circuit which is safe to use and capable of automatic measurement.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a meter box opening detection circuit, including a detection terminal positive electrode A, a detection terminal negative electrode B, and characterized in that: it also includes a first resistor R1, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first diode D1, a second diode D2, a transistor Q1, a signal input terminal IN, and a signal output terminal OUT;

[0007] The anode of the second diode D2 is connected to GND, the cathode of the second diode D2 is connected to the signal input terminal IN, and is connected to one end of the first capacitor C1, and the other end of the first capacitor C1 is connected to the positive electrode A of the detection terminal;

[0008] The collector of the transistor Q1 is connected to the signal output terminal OUT and is connected to the system main power supply through the first resistor R1; the emitter of the transistor Q1 is connected to GND; the base of the transistor Q1 is connected to the cathode of the first diode D1, and the anode of the first diode D1 is connected to GND; the third capacitor C3 is connected to the second diode D2 in parallel; one end of the second capacitor C2 is connected to the cathode of the first diode D1, and the other end thereof is connected to the cathode B of the detection terminal.

[0009] Preferably, a second resistor R2 is further included, one end of the second resistor R2 is connected to the cathode of the second diode D2, and the other end of the second resistor R2 is connected to one end of the first capacitor C1.

[0010] Preferably, the main power supply of the system is 3.3V.

[0011] Compared with the prior art, the invention has the following beneficial effects: ① it realizes the meter opening detection; ② it uses safety capacitors to isolate from strong electricity, which increases safety; ③ it has low power consumption design, which ensures that it can be powered only by batteries and can be detected when the city power is off. It adopts Y capacitor isolation and utilizes the characteristics of capacitors that can conduct AC signals. It does not need to add external batteries or specially designed meter boxes, and it can ensure that the detection function is still available when the external 220V AC power is off. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a circuit diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0013] The present invention will be further described below in conjunction with the accompanying drawings:

[0014] Embodiment 1

[0015] like Figure 1 As shown, a meter box opening detection circuit includes a detection terminal positive electrode A, a detection terminal negative electrode B, and also includes a first resistor R1, a second resistor R2, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first diode D1, a second diode D2, a transistor Q1, a signal input terminal IN, and a signal output terminal OUT;

[0016] The anode of the second diode D2 is connected to GND, and the cathode thereof is connected to the signal input terminal IN; one end of the second resistor R2 is connected to the cathode of the second diode D2, and the other end is connected to one end of the first capacitor C1; the other end of the first capacitor C1 is connected to the anode A of the detection terminal;

[0017] The collector of the transistor Q1 is connected to the signal output terminal OUT, and is connected to the 3.3V system main power supply through the first resistor R1; the emitter of the transistor Q1 is connected to GND; the base of the transistor Q1 is connected to the cathode of the first diode D1, and the anode of the first diode D1 is connected to GND; the third capacitor C3 is connected to the second diode D2 in parallel; one end of the second capacitor C2 is connected to the cathode of the first diode D1, and the other end thereof is connected to the cathode B of the detection terminal.

[0018] The function of the second resistor R2 is to limit the current when the chip pin charges the capacitor to prevent the chip pin from being damaged by the output large current. In addition, it can also protect the chip pin when there is external static electricity input.

[0019] The working principle of the present invention is as follows:

[0020] like Figure 1 As shown, when the meter box is closed, the positive pole A and the negative pole B of the detection terminal are short-circuited, the signal input terminal IN is connected to the MCU push-pull output high level, and the first capacitor C1 and the second capacitor C2 are charged; the CE pole of the transistor Q1 is turned on, and the signal output terminal OUT is low level; when the first capacitor C1 and the second capacitor C2 are fully charged, the CE pole of the transistor Q1 is not turned on, and the signal output terminal OUT is high level.

[0021] When the meter box is opened, the positive pole A of the detection terminal and the negative pole B of the detection terminal are open, and the signal input terminal IN is connected to the MCU push-pull output high level, so the first capacitor C1 and the second capacitor C2 cannot be charged; the CE pole of the transistor Q1 is not conducting, and OUT is high level; because the positive pole A and the negative pole B of the detection terminal are actually connected to the meter box by wires, and a parasitic capacitance of about 50pF is generated, the first capacitor C1 and the second capacitor C2 can still be charged.

[0022] It is necessary to add a third capacitor C3. The capacitance of the third capacitor C3 is 1nF, which is 20 times the parasitic capacitance. According to the formula capacitive reactance XC=1 / (2ΠfC), the capacitive reactance is 1 / 20 of the parasitic capacitance, that is, the divided voltage is also 1 / 20, 3.3V*(1 / 20)=0.165V<0.65V, and the transistor Q1 is not conducting.

[0023] Designed to withstand 4kV AC power frequency voltage:

[0024] The first capacitor C1 and the second capacitor C2 are Y1 safety capacitors with a capacity of 1nF and a withstand voltage of 4000VAC between the terminals.

[0025] According to the formula capacitive reactance XC=1 / (2ΠfC), XC1=XC2=1 / (2*Π*50Hz*1nF)=3.18MΩ,

[0026] Total leakage current = 4kV / 3.18MΩ*2 = 2.5mA<5mA meets the safety standard. The PN junction formed between the first diode D1, the second diode D2 and the BE of the transistor Q1 has a freewheeling function to ensure that the leakage current passes.

[0027] Anti-static design:

[0028] The second diode D2 is a transient suppression diode with a parasitic capacitance less than 1 pf. When there is electrostatic interference at the A terminal, the second resistor R2 limits the electrostatic current and the second diode D2 limits the electrostatic voltage to protect the chip pins.

[0029] Low power design:

[0030] The input signal of the signal input terminal IN is a square wave signal with a frequency of 1 Hz and a duty cycle of 50%.

[0031] When the positive electrode A of the detection terminal and the negative electrode B of the detection terminal are disconnected, the first capacitor C1 and the second capacitor C2 will not be charged, and the transistor Q1 will not be turned on, so there is no power consumption.

[0032] When the positive electrode A and the negative electrode B of the detection terminal are short-circuited, the first capacitor C1, the second capacitor C2, and the third capacitor C3 are connected in series, and the total capacitance is 1 / 3nF;

[0033] According to the formula W=0.5CU²=UIt; the average charging current per second is I=(0.5CU²) / (Ut)=5.5nA;

[0034] Transistor Q1 is an NPN tube with an amplification factor of 250~600 times. The resistance of R1 is 100kΩ. The conduction time of transistor Q1 varies depending on the amplification factor of the transistor. According to actual measurement, it is about 20us.

[0035] The average current of 3.3V power supply is obtained = 3.3V / R1*(20us / 1s) = 6.6pA;

[0036] Therefore, the average power consumption of the whole circuit is less than 1uA and can be ignored. Only the power consumption of the microcontroller's timed wake-up needs to be considered.

[0037] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A meter box opening detection circuit, comprising a detection terminal positive electrode A and a detection terminal negative electrode B, characterized in that: It also includes a first resistor R1, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first diode D1, a second diode D2, a transistor Q1, a signal input terminal IN, and a signal output terminal OUT; The anode of the second diode D2 is connected to GND, the cathode of the second diode D2 is connected to the signal input terminal IN, and is connected to one end of the first capacitor C1, and the other end of the first capacitor C1 is connected to the positive electrode A of the detection terminal; The collector of the transistor Q1 is connected to the signal output terminal OUT and is connected to the system main power supply through the first resistor R1; the emitter of the transistor Q1 is connected to GND; the base of the transistor Q1 is connected to the cathode of the first diode D1, and the anode of the first diode D1 is connected to GND; the third capacitor C3 is connected to the second diode D2 in parallel; one end of the second capacitor C2 is connected to the cathode of the first diode D1, and the other end thereof is connected to the cathode B of the detection terminal.

2. The meter box opening detection circuit according to claim 1, characterized in that: The device further includes a second resistor R2 , one end of which is connected to the cathode of the second diode D2 , and the other end of which is connected to one end of the first capacitor C1 .

3. The meter box opening detection circuit according to claim 2, characterized in that: The main power supply of the system is 3.3V.

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