Inductive proximity switch temperature compensation circuit

Abstract

The inductive proximity switch temperature compensation circuit comprises an LC oscillation circuit, a power supply circuit, a rectifier filter circuit, a signal detection and processing circuit and a temperature compensation circuit; the LC oscillation circuit, the power supply circuit, the rectifier filter circuit, the signal detection and processing circuit and the temperature compensation circuit are installed in a shell; the signal output end of the LC oscillation circuit and the signal input end of the rectifier filter circuit are connected through a wire; the signal output ends of the temperature compensation circuit and the rectifier filter circuit and the signal input end of the signal detection and processing circuit are respectively connected through wires; and the power output end of the signal detection and processing circuit and the power input end of the relay are connected through a wire. The novel inductive proximity switch temperature compensation circuit can actively inject a compensation voltage with a specific function relationship with temperature into a later-stage signal processing circuit, and use the compensation signal to counteract the drift of the oscillation amplitude caused by temperature change, so as to stabilize the detection threshold at a constant level, thereby providing favorable technical support for stable operation of the inductive proximity switch.

Description

Technical Field

[0001] This utility model relates to the field of sensor technology, and in particular to an inductive proximity switch temperature compensation circuit. Background Technology

[0002] Inductive proximity switches are non-contact detection devices widely used in industrial automation control. Their core working principle utilizes an LC oscillation circuit. When a metal object approaches the sensing surface of the inductive proximity switch, eddy currents are generated within the metal object, causing a change in the equivalent impedance of the oscillation circuit. This results in an attenuation of the oscillation amplitude or a change in frequency, ultimately triggering a switch signal output through subsequent processing circuitry. However, existing inductive proximity switches have a significant technical drawback: poor temperature stability. Specifically, when the ambient temperature changes (e.g., within the industrial temperature range of -25℃ to +85℃), the switch's detection distance drifts. This directly leads to a decrease in detection reliability and may even cause malfunctions, severely impacting the stable operation of automated equipment.

[0003] The reasons for the poor temperature stability of inductive proximity switches are analyzed as follows: (1) Temperature characteristics of inductor coils: The resistivity of the copper wires of the inductor coils, which constitute the key components of the oscillation circuit, will increase with the temperature (copper has a positive temperature coefficient). This will lead to an increase in the equivalent series resistance of the coil, thereby causing a decrease in the Q value (quality factor) of the oscillation circuit. The decrease in Q value means a decrease in the oscillation amplitude, making it easier for the amplitude attenuation caused by the metal object to reach the trigger threshold of the subsequent circuit at the same distance, creating the illusion of "the detection distance is longer". (2) Temperature characteristics of capacitor components: The capacitors used in the oscillation circuit, especially ceramic capacitors, usually have a temperature coefficient (such as NPO, X7R, Y5V, etc., different materials have very different temperature stability). The change in capacitance value will directly change the resonant frequency of the oscillation circuit, thereby affecting the reference point of the entire detection system. In the existing technology, the conventional methods used in the industry to solve this problem include: selecting expensive components with better temperature characteristics (such as precision capacitors and magnetic core materials with low temperature drift), performing complex software algorithm compensation, or conducting wide-temperature testing and manual screening and matching during production. The above methods are either costly, have complex production processes, or have limited compensation effects, and cannot solve the temperature drift problem efficiently and at low cost. Utility Model Content

[0004] To overcome the drawbacks of existing inductive proximity switches due to structural limitations, as described in the background art, this invention provides an inductive proximity switch temperature compensation circuit that introduces a compensation voltage that has a specific functional relationship with temperature. This compensation voltage can be actively injected into the subsequent signal processing circuit, and the compensation signal is used to counteract the drift in oscillation amplitude caused by temperature changes, thereby stabilizing the detection threshold at a constant level. This provides favorable technical support for accurately controlling the operation of related electrical equipment.

[0005] The technical solution adopted by this utility model to solve its technical problem is:

[0006] An inductive proximity switch temperature compensation circuit includes an LC oscillation circuit and a power supply circuit for the inductive proximity switch, and also includes a rectifier and filter circuit, a signal detection and processing circuit, and a temperature compensation circuit. The LC oscillation circuit, power supply circuit, rectifier and filter circuit, signal detection and processing circuit, and temperature compensation circuit are installed inside the housing of the inductive proximity switch. The power output terminal of the power supply circuit and the power input terminals of the LC oscillation circuit, rectifier and filter circuit, signal detection and processing circuit, and temperature compensation circuit are connected by wires. The signal output terminal of the LC oscillation circuit and the signal input terminal of the rectifier and filter circuit are connected by wires. The signal output terminals of the temperature compensation circuit and the rectifier and filter circuit are connected to the two signal input terminals of the signal detection and processing circuit by wires. The power output terminal of the signal detection and processing circuit and the power input terminal of the relay are connected by wires.

[0007] Furthermore, the power supply circuit includes a protection diode and a diode, a DC-to-DC power supply module, and a Zener diode connected by wires. The positive terminal of the diode is connected to one end of the protection diode, the negative terminal of the diode is connected to the positive power input terminal of the DC-to-DC power supply module, the power output terminal of the DC-to-DC power supply module is connected to the negative terminal of the Zener diode, and the positive terminal of the Zener diode is connected to the negative power input terminal, the negative power output terminal of the DC-to-DC power supply module, and the other end of the protection diode.

[0008] Furthermore, the rectifier filter circuit includes a capacitor, a diode, and a resistor that are electrically connected. One end of the first capacitor is connected to the positive terminal of the first diode. The negative terminals of the first and second diodes, one end of the second capacitor, and one end of the resistor are connected. The positive terminal of the second diode is connected to the other end of the second capacitor and the other end of the resistor.

[0009] Furthermore, the signal detection and processing circuit includes a resistor, a transistor, an operational amplifier, a protection diode, and a fuse connected by wires. The output terminal of the operational amplifier is connected to one end of the resistor, the other end of the resistor is connected to the base of the transistor, the collector of the transistor is connected to one end of the fuse and one end of the protection diode, and the other end of the protection diode is connected to the emitter of the transistor and the negative power input terminal of the operational amplifier.

[0010] Furthermore, the temperature compensation circuit includes a resistor and an NTC thermistor connected by wires. One end of the first resistor, one end of the second resistor, and one end of the NTC thermistor are connected. The other end of the first resistor is connected to one end of the fourth resistor and one end of the fifth resistor. The other end of the second resistor is connected to the other end of the NTC thermistor and the other end of the fifth resistor.

[0011] Compared with the prior art, the advantages of this utility model are: (1) High precision and high stability: Through the active and closed-loop analog compensation mechanism, the temperature drift can be offset in real time and continuously, and the temperature drift of the detection distance can be controlled within a very small range (the change is less than ±5% in the entire working temperature range), which improves the detection accuracy and long-term reliability of the product; (2) Low cost: The core compensation circuit can be implemented by common and low-cost analog components (such as NTC and conventional resistors), without the need to select expensive low-temperature drift special components, and without the need to add complex software and processors, which effectively controls the product cost; (3) Easy to produce and debug: It eliminates the cumbersome wide-temperature test and manual calibration and pairing links in the traditional scheme, simplifies the production process, improves production efficiency, and ensures good consistency. Once the circuit parameters are determined, there is basically no need to adjust them during mass production; (4) Wide adaptability: The core principle (sensing temperature - generating compensation signal - injecting key point) can be applied to inductive proximity switches of various topologies, and has good universality and portability; (5) Fast response: The compensation response speed based on the analog circuit is extremely fast, which can keep up with the rapid change of temperature and has no compensation delay. In summary, this new invention effectively overcomes the shortcomings of existing technologies, providing a high-performance, low-cost, and easy-to-implement temperature compensation solution for inductive proximity switches, thus possessing high commercial value and market prospects. Attached Figure Description

[0012] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0013] Figure 1 This is a schematic block diagram of the structure of this utility model.

[0014] Figure 2 , 3 Figure 4 is the circuit diagram of this utility model. Detailed Implementation

[0015] Figure 1 , 2 As shown in Figures 3 and 4, the temperature compensation circuit for the inductive proximity switch includes an LC oscillation circuit 1 and a power supply circuit 2 for the inductive proximity switch, and also has a rectifier and filter circuit 3, a signal detection and processing circuit 4, and a temperature compensation circuit 5; the LC oscillation circuit 1, the power supply circuit 2, the rectifier and filter circuit 3, the signal detection and processing circuit 4, and the temperature compensation circuit 5 are installed inside the housing of the inductive proximity switch.

[0016] Figure 1 , 2 As shown in Figures 3 and 4, the power supply circuit includes protection diodes D3 and D1, a DC-to-DC power supply module U1, and a Zener diode D2 connected via circuit board wiring. The anode of diode D1 is connected to one end of protection diode D3, and the cathode of diode D1 is connected to pin 1 of the positive power input terminal of DC-to-DC power supply module U1. The positive power output terminal pin 3 of DC-to-DC power supply module U1 is connected to the cathode of Zener diode D2. The anode of Zener diode D2 is connected to pin 2 of the negative power input terminal of DC-to-DC power supply module U1, pin 4 of the negative power output terminal, and the other end of protection diode D2. The rectifier and filter circuit includes capacitors C1 and C2, diodes D4 and D6, and a resistor R2 connected via circuit board wiring. One end of the first capacitor C3 is connected to the anode of the first diode D4. The cathodes of the first diode D4 and the second diode D6, one end of the second capacitor C2, and one end of the resistor R2 are connected. The anode of the second diode D6, the other end of the second capacitor C2, and the other end of the resistor R2 are connected. The signal detection and processing circuit includes a resistor R1, a transistor Q1, an operational amplifier U2, a protection diode D5, and a fuse F1, all connected via circuit board wiring. The output pin 4 of the operational amplifier U2 is connected to one end of resistor R1, and the other end of resistor R1 is connected to the base of transistor Q1. The collector of transistor Q1 is connected to one end of fuse F1 and one end of protection diode D6. The other end of protection diode D5 is connected to the emitter of transistor Q1 and the negative power input pin 2 of the operational amplifier U2. The temperature compensation circuit includes resistors R3, R4, R6, and R7, and an NTC thermistor R5, all connected via circuit board wiring. One end of the first resistor R3, one end of the second resistor R4, and one end of the NTC thermistor R5 (negative temperature coefficient thermistor) are connected. The other end of the first resistor R3 is connected to one end of the fourth resistor R7 and one end of the fifth resistor R6. The other end of the second resistor R4 is connected to the other ends of the NTC thermistor R5 and the other ends of the fifth resistor R6.

[0017] Figure 1 , 2As shown in Figures 3 and 4, the two ends of the protection diode D3 at the power input terminal of the power supply circuit and the two poles of the DC 9-32V power supply are connected by wires respectively. The power output terminal of the power supply circuit, pins 3 and 4 of the DC to DC power module U1, the power input terminal of the LC oscillation circuit (mature existing technology, which will not be described in detail in this application), the other end of the capacitor C2 at the power input terminal of the rectifier filter circuit, the power input terminals 5 and 2 of the operational amplifier U2 of the signal detection and processing circuit, and one end of the resistor R3 and the other end of the resistor R7 at the power input terminal of the temperature compensation circuit are connected by wires respectively. The signal output terminal of the LC oscillator circuit and the signal input terminal of the rectifier filter circuit are connected by wires. One end of the resistor R7 at the signal output terminal of the temperature compensation circuit, the negative terminal of the diode D4 at the signal output terminal of the rectifier filter circuit, and the non-inverting input terminal (pin 1) and the inverting input terminal (pin 3) of the operational amplifier U2 in the signal detection and processing circuit are connected by wires. The other end of the fuse F1 at the power output terminal of the signal detection and processing circuit, the positive power output terminal (pin 3) of the DC-to-DC power supply module U1, and the signal input terminal of the electrical equipment are connected by wires.

[0018] Figure 1 , 2As shown in Figures 3 and 4, after the power supply enters the power input terminal of the power supply circuit, the DC-to-DC power module U1 outputs a stable 5V DC power supply at pins 3 and 4, which then enters the power input terminals of the LC oscillation circuit, rectifier and filter circuit, signal detection and processing circuit, and temperature compensation circuit, enabling these circuits to operate. The working process of this novel device is as follows: In practical applications, when a metal object approaches this device, the LC oscillator generates a high-frequency oscillation signal. The rectifier and filter circuit first couples the oscillation signal through capacitor C1, and then sequentially passes it through high-frequency rectifier diodes D4 and D6 (utilizing the unidirectional conductivity of diodes to eliminate the negative half-cycle (half-wave) and generate pulsating DC), converting the AC oscillation signal output by the LC oscillator into a DC voltage signal. After filtering by capacitor C2, a cleaner and smoother DC voltage signal is injected into the inverting input pin 3 of operational amplifier U2 and compared with a fixed reference voltage. The reference voltage is generated by the temperature compensation circuit, which uses a... A negative temperature coefficient (NTC) thermistor R5 is used to construct a resistor network. This network consists of resistor R4 and the NTC thermistor R5 connected in parallel. This parallel resistor is then connected in series with resistor R6, and then in parallel with resistor R3. Finally, this equivalent resistor is connected in series with resistor R7 to divide the voltage and obtain a reference voltage, which is injected into the non-inverting input (pin 1) of the operational amplifier. When the temperature changes, the resistance of the NTC thermistor R5 (the higher the temperature, the lower the resistance and the lower the voltage division; the lower the temperature, the higher the resistance and the higher the voltage division) changes, and the reference voltage changes accordingly. This dynamically adjusts the threshold of the decision operational amplifier U2 to track the changes in the oscillation amplitude, thereby keeping the difference between (oscillation amplitude and threshold) constant. In the signal detection and processing circuit, operational amplifier U2 is used as a comparator. When a metal object approaches, the oscillation amplitude of the LC oscillator attenuates. When the amplitude attenuates to below the reference voltage, pin 4 of operational amplifier U2 outputs a high level. This high level drives the collector and emitter of transistor Q1 to conduct through the current-limiting resistor R1. Then, the output is pulled down to ground through ESD protection diode D5 and fuse F1, and the output pin becomes low. This low-level signal is then output to the signal input terminal of the device via pin 3 of the positive power supply module U1. When the metal object moves away from the device (detection distance 40mm), the oscillation amplitude increases. When the amplitude increases to above the reference voltage, pin 2 outputs a low level, the collector and emitter of transistor Q1 turn off, and the output pin becomes floating, thus generating the final switching output signal.

[0019] Figure 1 , 2As shown in Figures 3 and 4, through the operation of all the circuits described above, this novel rectifier and filter circuit actively injects a compensation voltage that has a specific functional relationship with temperature into the subsequent signal processing circuit. This compensation signal is used to counteract the drift in oscillation amplitude caused by temperature changes, thereby stabilizing the detection threshold at a constant level. The signal detection and processing circuit converts the AC oscillation signal output from the LC oscillator into a DC voltage signal and compares it with a fixed reference voltage to generate the final switching output signal. In the temperature compensation circuit, a negative temperature coefficient (NTC) thermistor is used to construct a resistor network. By carefully configuring the parameters of the resistor network, the output of the circuit becomes a compensation voltage that has a specific functional relationship with temperature T. This compensation voltage is injected into the reference terminal of the operational amplifier. When the temperature changes, the reference voltage changes accordingly, dynamically adjusting the decision threshold of the comparator to track the change in oscillation amplitude, thereby maintaining the difference (oscillation amplitude - threshold) constant. This novel design provides favorable technical support for the accurate control of related electrical equipment. Figure 2 , 3 In section 4, the power module U1 is model TPS7B6950QDCYRQ1; transistor Q1 is an NPN transistor; diode D1 prevents reverse connection of the power input; Zener diode D2 clamps the voltage to 5V, providing overvoltage protection; protection diodes D3 and D5 protect the circuit from electrostatic discharge and surge voltage damage; diodes D4 and D6 provide high-frequency rectification; and fuse F1 provides overcurrent protection. The models of other electronic components in this new type are already marked in the accompanying drawings and will not be repeated here.

[0020] Those skilled in the art should understand that although this specification describes embodiments, the embodiments do not necessarily contain only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. Therefore, the scope of protection of this invention is defined by the claims.

Claims

1. Inductive proximity switch temperature compensation circuit, comprising an LC oscillation circuit of an inductive proximity switch, a supply circuit, characterized in that It also includes a rectifier and filter circuit, a signal detection and processing circuit, and a temperature compensation circuit; the LC oscillation circuit, power supply circuit, rectifier and filter circuit, signal detection and processing circuit, and temperature compensation circuit are installed inside the housing of the inductive proximity switch; the power output terminal of the power supply circuit and the power input terminals of the LC oscillation circuit, rectifier and filter circuit, signal detection and processing circuit, and temperature compensation circuit are connected by wires; the signal output terminal of the LC oscillation circuit and the signal input terminal of the rectifier and filter circuit are connected by wires; the signal output terminals of the temperature compensation circuit and the rectifier and filter circuit and the two signal input terminals of the signal detection and processing circuit are respectively connected by wires; the power output terminal of the signal detection and processing circuit and the power input terminal of the relay are connected by wires.

2. The inductive proximity switch temperature compensation circuit of claim 1, wherein, The power supply circuit includes a protection diode and a diode, a DC-to-DC power supply module, and a Zener diode connected by wires. The positive terminal of the diode is connected to one end of the protection diode, the negative terminal of the diode is connected to the positive power input terminal of the DC-to-DC power supply module, the power output terminal of the DC-to-DC power supply module is connected to the negative terminal of the Zener diode, and the positive terminal of the Zener diode is connected to the negative power input terminal, the negative power output terminal of the DC-to-DC power supply module, and the other end of the protection diode.

3. The inductive proximity switch temperature compensation circuit of claim 1, wherein, The rectifier filter circuit includes a capacitor, a diode, and a resistor that are electrically connected. One end of the first capacitor is connected to the positive terminal of the first diode. The negative terminals of the first and second diodes, one end of the second capacitor, and one end of the resistor are connected. The positive terminal of the second diode is connected to the other end of the second capacitor and the other end of the resistor.

4. The inductive proximity switch temperature compensation circuit of claim 1, wherein, The signal detection and processing circuit includes a resistor, a transistor, an operational amplifier, a protection diode, and a fuse connected by wires. The output terminal of the operational amplifier is connected to one end of the resistor, and the other end of the resistor is connected to the base of the transistor. The collector of the transistor is connected to one end of the fuse and one end of the protection diode, and the other end of the protection diode is connected to the emitter of the transistor and the negative power input terminal of the operational amplifier.

5. The inductive proximity switch temperature compensation circuit of claim 1, wherein, The temperature compensation circuit includes a resistor and an NTC thermistor connected by wires. One end of the first resistor, one end of the second resistor, and one end of the NTC thermistor are connected. The other end of the first resistor is connected to one end of the fourth resistor and one end of the fifth resistor. The other end of the second resistor is connected to the other end of the NTC thermistor and the other end of the fifth resistor.

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