CN214669325U

CN214669325U - Preceding stage detection circuit for alternating current line hunting and line hunting instrument

Info

Publication number: CN214669325U
Application number: CN202120556479.2U
Authority: CN
Inventors: 李铮; 张志鹏
Original assignee: TP Link Technologies Co Ltd
Current assignee: TP Link Technologies Co Ltd
Priority date: 2021-03-17
Filing date: 2021-03-17
Publication date: 2021-11-09
Anticipated expiration: 2031-03-17

Abstract

The utility model belongs to the technical field of detect, a preceding stage detection circuitry and hunting appearance for exchanging hunting is related to, preceding stage detection circuitry includes induction antenna and amplifier circuit, induction antenna includes an inductance, the one end of inductance is connected amplifier circuit, the other end of inductance is through an input resistance ground connection, through adjusting the input resistance size is in order to adjust preceding stage detection circuitry's voltage gain and current gain's proportion. In this way, gain adjustment of the input voltage or input current can be achieved, so that the output signal can be identified and the line seeking is successful.

Description

Preceding stage detection circuit for alternating current line hunting and line hunting instrument

Technical Field

The application belongs to the technical field of detection, and particularly relates to a preceding stage detection circuit and a hunting instrument for alternating current hunting.

Background

The network hunting instrument is a measuring device applied to a network wiring scene, and is used for quickly finding a target line from a large number of network lines. The conventional network hunting instrument products mostly adopt a non-contact working mode, and a hunting master (hereinafter, referred to as a master) and a hunting slave (hereinafter, referred to as a slave) are matched to complete hunting operation. The host computer transmits a specific alternating current signal to the network cable, a probe at the front end of the slave computer is used to approach the network cable to be detected (hereinafter referred to as the network cable for short), the probe can detect the signal transmitted by the host computer in the network cable, identify the signal and finally send out a prompt tone to indicate that the network cable approaching is the target network cable for line searching.

The working principle of the slave machine is to detect the signals radiated by the near field of the network cable, so the performance of the front stage detection circuit directly influences the performance of the slave machine. The existing products can be divided into a current type preceding stage circuit and a voltage type preceding stage circuit according to different detection target quantities of the detection preceding stage circuit. The network hunting instrument can be divided into two use scenes, namely no-load hunting (one end of a network cable is connected with a host, and the other end is suspended) and load hunting (one end of the network cable is connected with the host, and the other end is connected with a network product, such as a switch and a router) according to different termination conditions of a target network cable in use.

When no-load line seeking is carried out, one end of a network cable is connected with a host, the other end of the network cable is suspended, signals on a target network cable are mainly voltage signals, and current in the network cable is very small. In this scenario, a slave using a current mode front stage circuit may not detect a specific signal sent by the master because the current is too small; when the line is searched with load, one end of the target network line is connected with the host computer, and the other end is connected with the network equipment. In a scenario where a part of network devices are internally short-circuited between network cable pairs, the network cable is close to the network device, and the voltage is very small but the current is relatively large due to the short-circuit of the network cable. In such a scenario, if a slave of the voltage type front stage circuit is used, a hunting failure may easily occur because the voltage signal is too small.

It can be seen that both of the existing front-end circuits may cause a line-seeking failure due to insufficient voltage or current gain in one of the usage scenarios.

SUMMERY OF THE UTILITY MODEL

An object of the embodiments of the present application is to provide a pre-stage detection circuit and a line finder for ac line hunting, so as to solve the problem of line hunting failure caused by insufficient voltage or current gain of the current line finder.

The embodiment of the application provides a preceding stage detection circuit for exchanging hunting, including induction antenna and amplifier circuit, induction antenna includes an inductance, the one end of inductance is connected amplifier circuit, the other end of inductance is through an input resistance ground connection, through adjusting the input resistance size is in order to adjust preceding stage detection circuit's voltage gain and current gain's proportion.

In one embodiment, the amplifying circuit includes a first resistor, a second resistor, and an operational amplifier, wherein one end of the first resistor is connected to one end of the inductor, the other end of the first resistor is connected to the inverting input terminal of the operational amplifier, and the second resistor is connected between the inverting input terminal and the output terminal of the operational amplifier.

In one embodiment, the gain of the pre-stage detection circuit to the induced voltage or the induced current is adjusted by adjusting the resistance value of the first resistor and/or the second resistor.

In one embodiment, the input resistance comprises at least one resistor.

The embodiment of the application also provides a line hunting instrument, which comprises the preceding stage detection circuit for alternating current line hunting.

The preceding stage detection circuit and the hunting appearance for exchanging hunting that this application embodiment provided will be as induction antenna's inductance ground connection through an input resistance, through the size of adjusting this input resistance, can realize the proportion to voltage gain and current gain in the preceding stage detection circuit, so, can realize the gain adjustment to input voltage or input current for output signal can be discerned, and the hunting is successful.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.

FIG. 1 is a schematic block diagram of a conventional voltage mode front stage circuit;

FIG. 2 is a schematic block diagram of a conventional current mode front stage circuit;

FIG. 3 is a schematic block diagram of a pre-stage detection circuit for AC line seeking according to an embodiment of the present disclosure;

FIG. 4 is an equivalent schematic diagram of the sensed alternating voltage signal of the pre-detection circuit of FIG. 3;

fig. 5 is an equivalent schematic diagram of the sensed alternating current signal of the pre-detection circuit shown in fig. 3.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

The existing products can be divided into a current type front-end circuit and a voltage type front-end circuit according to different detection target quantities of the detection front-end circuit.

Referring to fig. 1, a schematic block diagram of a conventional voltage type front stage circuit is shown, which uses a coupling capacitor between a line to be tested (such as a network cable) and an antenna to detect a signal in the network cable. The front-stage circuit is characterized in that a suspended metal material is used as an antenna, and the antenna is directly connected to the input end of the amplifying circuit. An alternating voltage signal of the network cable can be input through a coupling capacitor C1 formed by a line to be tested and the antenna, and the resistors R1 and R2 are used for adjusting the input resistor and the front-stage gain. The voltage type front stage circuit utilizes a coupling capacitor C1 to detect only an alternating voltage signal in a line to be tested.

Referring to fig. 2, a schematic block diagram of a conventional current-mode pre-stage circuit is shown, which uses mutual inductance between a line to be tested and an antenna to detect a signal in a network cable, and the pre-stage circuit is characterized in that the antenna is a 2-terminal element (usually, an inductor is used to increase the mutual inductance between the network cable and the antenna), one terminal of the antenna is connected to an input terminal of an amplifying circuit, and the other terminal of the antenna is connected to ground. Alternating current signals of a line to be tested are input through mutual inductance L1, and the resistors R1 and R2 are used for adjusting input resistors and pre-stage gain. The current type front stage circuit utilizes mutual inductance L1 and can only detect alternating current signals on a line to be detected.

Referring to fig. 3, the embodiment of the present application provides a pre-detection circuit for ac line hunting applicable to a line finder, including an inductive antenna 10 and an amplifying circuit 20, where the inductive antenna 10 includes an inductor L0, one end of the inductor L0 is connected to the amplifying circuit 20, the other end of the inductor L0 is grounded through an input resistor Rin, and the ratio of the voltage gain and the current gain of the pre-detection circuit is adjusted by adjusting the magnitude of the input resistor Rin. When the inductor L0 is used as the inductive antenna 10, when the inductive antenna 10 is close to the line to be tested, 2 parasitic quantities exist between the inductor L0 and the line to be tested: coupling capacitance (e.g., C1 in fig. 1) and mutual inductance L (e.g., L1 in fig. 2), which are respectively sensitive to the voltage signal and the current signal in the line to be tested.

Because the proportion of the voltage gain and the current gain is adjustable through the input resistor Rin, the pre-stage detection circuit can be simultaneously suitable for detecting an alternating current signal and an alternating voltage signal on a line to be detected, namely, the pre-stage detection circuit is suitable for both idle line seeking and on-load line seeking.

In one embodiment, the amplifying circuit 20 includes a first resistor R1, a second resistor R2, and an operational amplifier 21, wherein one end of the first resistor R1 is connected to one end of the inductor L0, the other end of the first resistor R1 is connected to the inverting input terminal of the operational amplifier 21, the second resistor R2 is connected between the inverting input terminal and the output terminal of the operational amplifier 21, and the non-inverting input terminal of the operational amplifier 21 is connected to a reference voltage Vref, thereby forming an inverting proportional amplifying circuit.

There are 2 parasitic quantities between the inductance L0 and the line under test: the coupling capacitance (e.g., C1 in fig. 1) and the mutual inductance (e.g., L1 in fig. 2) are sensitive to the voltage signal and the current signal in the line under test, and are analyzed in detail as follows.

Voltage signal:

the alternating voltage signal on the line to be tested can only be input into the induction antenna 10 through the coupling capacitor C1, and the detection principle can be simplified as shown in fig. 4.

The ac voltage source Vac represents a voltage signal in the line to be tested, the coupling capacitor C1 is a coupling capacitor between the inductor L0 and the line to be tested, and the input resistor Rin is connected in parallel with the first resistor R1 to form an input resistor of the front-stage circuit. C2 is the coupling capacitance between a slave (such as a seeker slave including the pre-stage detection circuit for ac hunting of the present application) and ground. Therefore, the input signal of the preceding stage detection circuit can be expressed as follows.

If the parallel resistance of R1 and Rin is set as R_inputImpedance of C1

Is represented by Z_C1Impedance of C2

Is represented by Z_C2When the gain of the operational amplifier is R2/R1 and R2/R1 is A, the voltage gain Gv can be expressed as:

current signal:

the alternating current signal on the line to be detected can only be input into the induction antenna 10 through the mutual inductance L1, and the detection principle can be simplified as shown in fig. 5. In which the alternating current I on the line to be tested_acAn alternating voltage LI can be induced on the induction antenna 10_acWhere L is the equivalent impedance of the mutual inductance L1.

In the above circuit, Rin is equivalent to the voltage source LI_acR1 is the input resistance of the amplifier circuit 20. The input signal of the amplifying circuit 20 can be expressed as follows.

The gain of the operational amplifier is R2/R1, and if R2/R1 is A, the current gain G of the pre-stage detection circuit_ICan be expressed as:

based on the above analysis, the voltage gain and current gain adjustment method can be known, and the ratio of the voltage gain and the current gain can be expressed as:

therefore, under the condition selected by the first resistor R1, when the position of the sensing antenna 10 and the line to be tested is fixed (at this time, the equivalent impedance L of the coupling capacitors C1, C2 and the mutual inductance L1 is determined), Gv/Gi is only related to the input resistor Rin, and the ratio of the voltage gain to the current gain can be adjusted by adjusting the resistance value of the input resistor Rin.

In addition, after the proportion of the voltage gain and the current gain is selected, the amplification factor a of the operational amplifier is adjusted to adjust the absolute values of the voltage gain and the current gain, that is, the final voltage gain and the current gain are adjusted by selecting the first resistor R1 and/or the second resistor R2, and the adjustable resistors can be adopted as the input resistor Rin, the first resistor R1 and the second resistor R2. As analyzed above, the pre-stage detection circuit can adjust the voltage gain and the current gain independently.

The preceding-stage detection circuit can independently adjust the gains of the sensed voltage signals and the sensed current signals, reasonably selects the resistance values of the input resistor Rin, the first resistor R1 and the second resistor R2, can ensure that the circuit has enough gains for the alternating voltage and the alternating current in a line to be detected, and ensures that a slave machine of a hunting instrument using the circuit cannot fail in two use scenes of no-load hunting and on-load hunting.

The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. The utility model provides a preceding stage detection circuit for exchanging hunting, includes induction antenna and amplifier circuit, its characterized in that, induction antenna includes an inductance, the one end of inductance is connected amplifier circuit, the other end of inductance is through an input resistance ground connection, through adjusting input resistance size is in order to adjust preceding stage detection circuit's voltage gain and current gain's proportion.

2. The pre-stage detection circuit for ac hunting according to claim 1, wherein the amplifying circuit comprises a first resistor, a second resistor and an operational amplifier, one end of the first resistor is connected to one end of the inductor, the other end of the first resistor is connected to the inverting input terminal of the operational amplifier, and the second resistor is connected between the inverting input terminal and the output terminal of the operational amplifier.

3. The pre-detection circuit for ac hunting according to claim 2, wherein the gain of the pre-detection circuit for induced voltage or induced current is adjusted by adjusting the resistance of the first resistor and/or the second resistor.

4. The pre-detection circuit for ac hunting as claimed in claim 1, 2 or 3, wherein said input resistance comprises at least one adjustable resistor.

5. A line finder comprising the pre-detection circuit for AC line hunting of any one of claims 1 to 4.