Logging instrument delay power supply protection circuit and method

Abstract

The invention discloses a time-delay power supply protection circuit and method for a logging instrument. The time-delay power supply protection circuit comprises a power supply change-over switch which is externally connected with a standby battery, a ground main power supply and an underground circuit; the delay control circuit is externally connected with a power supply change-over switch; the voltage monitoring comparison circuit is connected with the delay control circuit; the ground main power supply supplies power to the voltage monitoring comparison circuit and the underground circuit; and the standby battery supplies power to the underground circuit when the ground main power supply is powered off. When the system is powered off, after the voltage value of the main power supply is reduced to a certain threshold value, the voltage comparison protection circuit triggers the delay control circuit and the power supply change-over switch to be switched on, and power supply of the underground circuit is switched to a standby battery; after a timing circuit in the delay control circuit expires, the power change-over switch is controlled to be switched off, and power supply of the standby battery is automatically cut off. The stability and reliability of the underground logging instrument are improved, an underground circuit can still work continuously when a system breaks down and is powered off, and logging data are prevented from being lost.

Description

Technical Field

[0001] The invention belongs to the field of circuits and relates to a delayed power supply protection circuit and method for a well logging instrument. Background Art

[0002] Oil well logging is an engineering technology that uses various instruments to measure the rock physical parameters of underground formations and wellbore conditions. The logging system consists of underground instruments, data telemetry systems, long-line cables, and ground systems. The ground system supplies power to the underground instruments through long-line cables.

[0003] Since the working environment of downhole instruments is a high-temperature environment, which can reach up to 175-200°C, extremely high requirements are placed on the high-temperature performance of the circuits of downhole instruments. After the circuit of the downhole instrument reaches a certain temperature, some control components will not work properly after power failure and restart at high temperature. In addition, the key circuits of downhole instruments, such as data storage circuits, are also required to work uninterruptedly when the system is powered off, otherwise the logging data will be lost. The logging system is a relatively complex system. In actual logging operations, various technical failures are inevitable, and system power failure and restart are relatively common operations. Therefore, it is easy to cause the key circuits of downhole instruments to not work properly or data to be lost. How to ensure that the key circuits of downhole instruments work uninterruptedly when the system is powered off is a difficult problem that needs to be solved in logging. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the key circuit of the downhole instrument in the prior art cannot work normally or the data is lost, and to provide a delayed power supply protection circuit and method for the logging instrument.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A delayed power supply protection circuit for a well logging instrument comprises: a voltage monitoring and comparison circuit, a delay control circuit and a power supply switching switch;

[0007] The power switching switch is respectively connected to the backup battery, the main power supply on the ground and the downhole circuit; the delay control circuit is externally connected to the power switching switch; the voltage monitoring and comparison circuit is connected to the delay control circuit; the main power supply on the ground supplies power to the voltage monitoring and comparison circuit and the downhole circuit; the backup battery supplies power to the downhole circuit when the main power supply on the ground is cut off.

[0008] A further improvement of the present invention is:

[0009] Furthermore, the power switching switch includes: a MOS tube Q1 and a resistor R2; the source of the MOS tube Q1 is respectively connected to the backup power supply and one end of the resistor R2; the other end of the resistor R2 and the gate of the MOS tube Q1 are simultaneously connected to the delay control circuit; the drain of the MOS tube Q1 is connected to the downhole circuit.

[0010] Furthermore, a switching diode D2 is arranged between the main power supply on the ground and the downhole circuit; a switching diode D1 is arranged between the drain of the MOS tube Q1 and the downhole circuit; the anode of the switching diode D1 is connected to the drain of the MOS tube Q1; the cathode of the switching diode D1 is respectively connected to the cathode of the diode D2 and the downhole circuit; the anode of the diode D2 is connected to the main power supply on the ground.

[0011] Furthermore, the delay control circuit includes: resistor R4, resistor R3, 555 timer U3, resistor R5, capacitor C1, capacitor C2, capacitor C4 and transistor Q2; the VCC end of the 555 timer U3 is connected to one end of the resistor R4, one end of the resistor R5 and the RESET end of the 555 timer U3; the GND end of the 555 timer U3 is grounded; the THRES port and the DISCH port of the 555 timer U3 are respectively connected to the other end of the resistor R4 and the positive electrode of the capacitor C4; the negative electrode of the capacitor C4 is grounded; the CONT end of the 555 timer U3 is connected to the positive electrode of the capacitor C2; the negative electrode of the capacitor C2 is grounded; the TRIG port of the 555 timer is connected to the other end of the resistor R5 and the negative electrode of the capacitor C1; the positive electrode of the capacitor C1 is connected to the voltage monitoring comparison circuit; the resistor R3 is set at the TRIG port of the 555 timer and the base of the transistor Q2; the emitter of the transistor Q2 is grounded; the collector of the transistor Q2 is connected to the other end of the resistor R2 and the gate of the MOS tube Q1.

[0012] Furthermore, the voltage monitoring comparison circuit includes: a comparator U1 and a Zener diode D3; the output end of the comparator U1 is connected to the positive electrode of the capacitor C1 and VCC; the reverse input end of the comparator U1 is connected to VCC; the forward input end of the comparator U1 is connected to the negative electrode of the Zener diode D3 and VCC, and the positive electrode of the Zener diode D3 is grounded; the ground end of the comparator U1 is grounded; and the power supply end of the comparator U1 is connected to Vcc.

[0013] Furthermore, the voltage monitoring comparison circuit further includes: a resistor R6 and a resistor R1; the resistor R6 is arranged between VCC and the output terminal of the comparator U1; and the resistor R1 is arranged between the positive input terminal of the comparator U1 and VCC.

[0014] Further, VCC is connected to one end of the resistor R5, one end of the resistor R4, the VCC port and the RESET port of the 555 timer U3.

[0015] Furthermore, the backup battery, the main power supply on the ground and the downhole circuit are all grounded.

[0016] Furthermore, the MOS tube Q1 is a PMOS tube.

[0017] A method for a delayed power supply protection circuit of a logging instrument comprises: a voltage monitoring comparison circuit monitors the voltage value of a main power supply; when the system is powered off, the voltage value of the main power supply decreases; after the voltage decreases to a certain threshold, the voltage comparison protection circuit triggers a delay control circuit to start working, a power supply switching switch is closed, and the power supply of the downhole circuit is switched to a backup battery; after the timing expires, a timing circuit inside the delay control circuit controls the power supply switching switch to be disconnected, and the power supply of the backup battery is automatically cut off.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention connects the power switch to the backup battery, the main power supply on the ground and the downhole circuit respectively; the delay control circuit is connected to the power switch; the voltage monitoring comparison circuit is connected to the delay control circuit; the main power supply on the ground supplies power to the voltage monitoring comparison circuit and the downhole circuit; the backup battery supplies power to the downhole circuit when the main power supply on the ground is cut off. When the system is powered off, the voltage value of the main power supply decreases. After the voltage decreases to a certain threshold, the voltage comparison protection circuit triggers the delay control circuit to start working, the power switch is closed, and the power supply of the downhole circuit is switched to the backup battery; after the timing expires, the timing circuit inside the delay control circuit controls the power switch to disconnect, and the backup battery power supply is automatically cut off. The present invention improves the stability and reliability of the downhole logging instrument, so that when the system fails and the power is cut off, the key circuit of the downhole instrument can still continue to work for a period of time, protecting the downhole circuit, avoiding the loss of logging data, and other catastrophic effects caused by system power outage. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 The overall block diagram of the delayed power supply protection circuit of the well logging instrument of the present invention;

[0022] Figure 2 It is a principle block diagram of the delayed power supply protection circuit of the well logging instrument of the present invention;

[0023] Figure 3 A schematic diagram of an implementation scheme of a delayed power supply protection circuit for a well logging instrument of the present invention;

[0024] Figure 4 (a) is a schematic diagram of the voltage waveform of the ground main power supply;

[0025] Figure 4(b) is a schematic diagram of the output waveform of the comparator U1;

[0026] Figure 4 (c) is a schematic diagram of the output waveform of the 555 timer trigger terminal;

[0027] Figure 4 (d) is a schematic diagram of the charging waveform of the RC circuit;

[0028] Figure 4 (e) is a schematic diagram of the 555 timer output waveform. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0032] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0033] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0034] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0036] See also Figure 1 , Figure 2 and Figure 3The present invention discloses a delayed power supply protection circuit for a logging instrument, including: a voltage monitoring comparison circuit, a delay control circuit and a power switch; the power switch is respectively connected to a backup battery, a ground main power supply and a downhole circuit; the delay control circuit is externally connected to the power switch; the voltage monitoring comparison circuit is connected to the delay control circuit; the ground main power supply supplies power to the voltage monitoring comparison circuit and the downhole circuit; the backup battery supplies power to the downhole circuit when the ground main power supply is powered off. The power switch includes: a PMOS tube Q1 and a resistor R2; the source of the PMOS tube Q1 is respectively connected to the backup power supply and one end of the resistor R2; the other end of the resistor R2 and the gate of the PMOS tube Q1 are simultaneously connected to the delay control circuit; the drain of the PMOS tube Q1 is connected to the downhole circuit. A switching diode D2 is arranged between the main power supply on the ground and the downhole circuit; a switching diode D1 is arranged between the drain of the PMOS tube Q1 and the downhole circuit; the anode of the switching diode D1 is connected to the drain of the PMOS tube Q1; the cathode of the switching diode D1 is respectively connected to the cathode of the diode D2 and the downhole circuit; the anode of the diode D2 is connected to the main power supply on the ground. The delay control circuit includes: a resistor R4, a resistor R3, a 555 timer U3, a resistor R5, a capacitor C1, a capacitor C2, a capacitor C4 and a transistor Q2; the VCC end of the 555 timer U3 is connected to one end of the resistor R4, one end of the resistor R5 and the RESET end of the 555 timer U3; the GND end of the 555 timer U3 is grounded; the THRES port and the DISCH port of the 555 timer U3 are respectively connected to the other end of the resistor R4 and the positive electrode of the capacitor C4; the negative electrode of the capacitor C4 is grounded; the CONT end of the 555 timer U3 is connected to the positive electrode of the capacitor C2; the negative electrode of the capacitor C2 is grounded; the TRIG port of the 555 timer is connected to the other end of the resistor R5 and the negative electrode of the capacitor C1; the positive electrode of the capacitor C1 is connected to the voltage monitoring comparison circuit; the resistor R3 is set at the TRIG port of the 555 timer and the base of the transistor Q2; the emitter of the transistor Q2 is grounded; the collector of the transistor Q2 is connected to the other end of the resistor R2 and the gate of the PMOS tube Q1. The voltage monitoring comparison circuit includes: a comparator U1 and a voltage zener diode D3; the output end of the comparator U1 is connected to the positive electrode of the capacitor C1 and VCC; the reverse input end of the comparator U1 is connected to VCC; the positive input end of the comparator U1 is connected to the negative electrode of the voltage zener diode D3 and VCC, and the positive electrode of the voltage zener diode D3 is grounded; the ground end of the comparator U1 is grounded; the power supply end of the comparator U1 is connected to Vcc. The voltage monitoring comparison circuit also includes: a resistor R6 and a resistor R1; the resistor R6 is set between VCC and the output end of the comparator U1; the resistor R1 is set between the positive input end of the comparator U1 and VCC. VCC is connected to one end of the resistor R5, one end of the resistor R4, the VCC port of the 555 timer U3, and the RESET port. The backup battery, the main power supply on the ground, and the underground circuit are all grounded.

[0037] A method for a delayed power supply protection circuit of a logging instrument comprises: a voltage monitoring comparison circuit monitors the voltage value of a main power supply; when the system is powered off, the voltage value of the main power supply decreases; after the voltage decreases to a certain threshold, the voltage comparison protection circuit triggers a delay control circuit to start working, a power supply switching switch is closed, and the power supply of the downhole circuit is switched to a backup battery; after the timing expires, a timing circuit inside the delay control circuit controls the power supply switching switch to be disconnected, and the power supply of the backup battery is automatically cut off.

[0038] Example:

[0039] There are two power supplies for the downhole instrument circuit. One is from the main power supply on the ground, which is used for the normal operation of the instrument; the other is a backup battery, which is located in the circuit short section of the downhole instrument and is used to power the instrument circuit when the system is powered off. The two power supplies are provided to the downhole circuit after passing through the power protection circuit board. Figure 1 shown.

[0040] The power supply protection circuit is composed of a voltage monitoring and comparison circuit, a delay control circuit, and a power supply switch. Figure 2 As shown. The voltage monitoring comparison circuit is mainly composed of a voltage comparator. This circuit sets a comparison threshold voltage, which is lower than the main power voltage, to determine whether the main power is off. When the main power is off, the output of the comparison circuit will trigger the delay control circuit to start working. The delay control circuit is composed of a timing circuit and a switch control circuit, which is used to generate a control signal for the power switch. The power switch is composed of a switch tube, which is used to switch the instrument power supply to the backup battery when the main power is off.

[0041] The working process of the protection circuit is as follows: Under normal conditions, after the ground system is powered on, the ground main power supply is directly provided to the underground circuit through the protection circuit. The protection circuit monitors the voltage value of the main power supply. When the system is powered off, the voltage value of the main power supply decreases. After the voltage drops to a certain threshold, the voltage comparison protection circuit triggers the delay control circuit to start working, the power switch is closed, and the power supply of the underground circuit is switched to the backup battery; after the timing circuit inside the delay control circuit expires, the control power switch is disconnected, and the backup battery power supply is automatically cut off.

[0042] Figure 3This is a specific protection circuit implementation scheme. The circuit consists of a comparator U1, a 555 timer U2 and its peripheral circuits, a backup battery switching switch MOS tube Q1 and its control circuit, switching diodes D1 and D2, etc. The power supply of the downhole circuit is Vcc. The input of the comparator U1 is the power supply voltage of the downhole circuit and the threshold voltage provided by the voltage regulator tube. The output of the comparator U1 is connected to the trigger end of the 555 timer through the capacitor C1. The resistor R4 and the capacitor C4 form an RC charging and discharging circuit and a monostable circuit with the 555 timer. The MOS tube Q1 realizes the switching of the power supply. The on and off of the MOS tube Q1 is controlled by the transistor Q2, and the on and off of the transistor Q2 is controlled by the output of the 555 monostable circuit. Figure 3 The main power supply on the ground passes through diode D2 to the underground circuit. The power supply voltage here is represented by the network label VCC, and the input of the voltage monitoring and comparison circuit is also represented by VCC. The two are electrically connected.

[0043] The circuit works as follows:

[0044] Under normal working conditions, the power supply Vcc of the downhole circuit is directly provided by the main power supply on the ground through diode D2, and the power supply of the protection circuit is also provided by Vcc. The input voltage of the in-phase terminal of the comparator U1 is Vcc, and the voltage of the inverting terminal is the threshold voltage VT, which is provided by the voltage stabilizing diode D3.

[0045] Under normal main power supply state, Vcc is higher than the threshold voltage VT, the comparator outputs a high level, the TRIG end of the 555 timer is a high level, the OUT end of the 555 timer outputs a low level, the transistor Q2 is cut off, the VGS of the MOS tube Q1 is 0V, the MOS tube is cut off, and the backup battery is disconnected from the downhole circuit.

[0046] After the main power supply is turned off, Vcc decreases. When Vcc is lower than the threshold voltage VT, the comparator output changes from high level to low level. The waveform of the main power supply is as follows: Figure 4 As shown in (a), the waveform output by comparator U1 is as follows Figure 4 (b) as shown.

[0047] The output jump of comparator U1 generates a low level pulse at the TRIG port of 555 timer through capacitor C1, triggering the level inversion of OUT terminal of 555 timer and outputting high level. The waveform of TRIG pin of 555 timer is as follows: Figure 4 (c) as shown.

[0048] The high level output of the 555 timer controls the transistor Q2 to turn on. The voltage VGS between the gate and source of the MOS tube is equal to the battery voltage Vbat. When it exceeds the MOS tube conduction threshold voltage, the MOS tube is turned on. The backup battery power supply loads electricity to the downhole circuit through Q1 and D2, and the downhole circuit automatically switches to the backup battery power supply.

[0049] When the main power supply is cut off and the 555 timing circuit is triggered, Vcc charges C4 through R4. When the voltage of C4 is less than 2 / 3Vcc, the output of the 555 timer is always high, Q1 is always on, and the downhole circuit maintains the backup battery power supply. When the voltage of C4 is charged to 2 / 3Vcc, the OUT terminal of the 555 timer triggers the output of a low level. At the same time, since the discharge terminal of the 555 is enabled, the charge on C4 is quickly released, the output of the 555 will remain low, the MOS tube Q1 is turned off, and the backup battery power supply to the downhole circuit is disconnected. The charging waveform of C4 is as follows: Figure 4 As shown in (d), the output waveform of comparator U1 is as follows: Figure 4 (e) as shown.

[0050] The above realizes the time-delay power supply protection of the backup battery to the underground circuit after the main power supply is cut off. The power-off protection time is determined by the time constant of the RC circuit composed of R4 and C4. The duration of the backup battery power supply is:

[0051]

[0052] Wherein, Tw is the delay protection time, R is the resistance value of resistor R4, C is the capacitance value of capacitor C4, and Vcc is the power supply voltage value of the circuit.

[0053] The backup battery voltage is slightly lower than the main power supply voltage. If the main power supply is restored during the backup battery power supply period, D2 will be turned on, and Vcc will be higher than the battery voltage. At this time, diode D1 will be cut off and the backup battery power supply will be disconnected, thereby achieving the purpose of saving the backup battery power.

[0054] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A delayed power supply protection circuit for a well logging instrument, It is characterized in that include: Voltage monitoring comparison circuit, delay control circuit and power supply switching switch; The power switching switch is respectively connected to an external backup battery, a ground main power supply and an underground circuit; the delay control circuit is externally connected to a power switching switch; the voltage monitoring and comparison circuit is connected to the delay control circuit; the ground main power supply supplies power to the voltage monitoring and comparison circuit and the underground circuit; the backup battery supplies power to the underground circuit when the ground main power supply is cut off.

2. The delayed power supply protection circuit of the logging instrument according to claim 1, It is characterized in that The power switching switch includes: a MOS tube Q1 and a resistor R2; the source of the MOS tube Q1 is respectively connected to a backup power supply and one end of the resistor R2; the other end of the resistor R2 and the gate of the MOS tube Q1 are simultaneously connected to a delay control circuit; the drain of the MOS tube Q1 is connected to an underground circuit.

3. The delayed power supply protection circuit of the logging instrument according to claim 2, It is characterized in that A switching diode D2 is arranged between the main power supply on the ground and the downhole circuit; a switching diode D1 is arranged between the drain of the MOS tube Q1 and the downhole circuit; the anode of the switching diode D1 is connected to the drain of the MOS tube Q1; the cathode of the switching diode D1 is respectively connected to the cathode of the diode D2 and the downhole circuit; the anode of the diode D2 is connected to the main power supply on the ground.

4. The delayed power supply protection circuit of the logging instrument according to claim 3, It is characterized in that The delay control circuit includes: a resistor R4, a resistor R3, a 555 timer U3, a resistor R5, a capacitor C1, a capacitor C2, a capacitor C4 and a transistor Q2; The VCC terminal of the 555 timer U3 is connected to one end of the resistor R4, one end of the resistor R5 and the RESET terminal of the 555 timer U3; the GND terminal of the 555 timer U3 is grounded; the THRES port and the DISCH port of the 555 timer U3 are respectively connected to the other end of the resistor R4 and the positive electrode of the capacitor C4; the negative electrode of the capacitor C4 is grounded; the CONT terminal of the 555 timer U3 is connected to the positive electrode of the capacitor C2; the negative electrode of the capacitor C2 is grounded; the TRIG port of the 555 timer is connected to the other end of the resistor R5 and the negative electrode of the capacitor C1; the positive electrode of the capacitor C1 is connected to the voltage monitoring comparison circuit; the resistor R3 is set at the TRIG port of the 555 timer and the base of the transistor Q2; the emitter of the transistor Q2 is grounded; the collector of the transistor Q2 is connected to the other end of the resistor R2 and the gate of the MOS tube Q1.

5. The delayed power supply protection circuit of the logging instrument according to claim 4, It is characterized in that The voltage monitoring comparison circuit includes: a comparator U1 and a voltage zener diode D3; the output end of the comparator U1 is connected to the positive electrode of the capacitor C1 and VCC; the reverse input end of the comparator U1 is connected to VCC; the forward input end of the comparator U1 is connected to the negative electrode of the voltage zener diode D3 and VCC, and the positive electrode of the voltage zener diode D3 is grounded; the ground end of the comparator U1 is grounded; and the power supply end of the comparator U1 is connected to Vcc.

6. The delayed power supply protection circuit of the logging instrument according to claim 5, It is characterized in that The voltage monitoring comparison circuit further includes: a resistor R6 and a resistor R1; the resistor R6 is arranged between VCC and the output terminal of the comparator U1; the resistor R1 is arranged between the positive input terminal of the comparator U1 and VCC.

7. The delayed power supply protection circuit of the logging instrument according to claim 6, It is characterized in that The VCC is connected to one end of the resistor R5, one end of the resistor R4, the VCC port and the RESET port of the 555 timer U3.

8. The delayed power supply protection circuit of the logging instrument according to claim 7, It is characterized in that The backup battery, the ground main power supply and the underground circuit are all grounded.

9. The delayed power supply protection circuit of the logging instrument according to claim 8, It is characterized in that The MOS tube Q1 is a PMOS tube.

10. A method for a delayed power supply protection circuit for a logging instrument according to any of claims 1 to 9, It is characterized in that include: The voltage monitoring comparison circuit monitors the voltage value of the main power supply. When the system is powered off, the voltage value of the main power supply decreases. After the voltage drops to a certain threshold, the voltage comparison protection circuit triggers the delay control circuit to start working, and the power switching switch is closed to switch the power supply of the underground circuit to the backup battery; after the timing expires, the timing circuit inside the delay control circuit controls the power switching switch to disconnect, and the backup battery power supply is automatically cut off.

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