CN2133849Y - Detector for cable faults - Google Patents

Abstract

The utility model relates to a vibrator. The basic structure and theory of a detector for cable faults are that a crystal vibration source generates an accurate ultra-low frequency detection signal through frequency dividing and enlarging, and the accurate ultra-low frequency detection signal is sent to cable fault line pair; a receiver detects along the cable; the signal is accurately selected frequency; after high multiplying power is enlarged, the amplitude variation of the signal determines the position of the fault. Because the utility model adopts reducing the range from detection signal frequency to ultra low frequency and carrying out companding measures, the application range of the detector to fault core thread contact resistance is from the 0-2 K omega of techniques to 0-20 K omega. The efficiency of fault detection is remarkably enhanced, and the application range of the utility model is more extensive.

Description

Detector for cable faults

The utility model relates to the cable fault detector of obstacles such as a kind of swinging cross that is used for the exploration cable heart yearn, ground connection, insulation, this detection instrument is made up of oscillator and receiver two large divisions, and oscillator comprises ultra-low frequency signal source, amplifying circuit, interrupted oscillation control circuit and power supply; Receiver comprises probe, low noise input stage, frequency selection circuit, rectification circuit, indicating circuit, signal amplitude monitoring circuit and power supply.

The instrument of direct detection cable obstacle, it is a end at cable, by oscillator to selected barrier line to sending into detectable signal, this signal constitutes the loop through obstacle position heart yearn contact resistance (the core insulation material advances the conducting resistance of tide or water inlet formation), receiver receives the electromagnetic field that this signal forms by probe along cable, variation according to signal amplitude before and after the barrier point, determine the obstacle position, its use is simple to operate, particularly can be at the scene to obstacle position fixed point, this is the exclusive advantage that this quasi-instrument is different from the cable obstacle tester.Be well known that the cable fault locator of 6405 types at present, comprise A, B, three kinds of models of C, its structure adopts all-transistor circuity, the oscillator output signal frequency is 400 hertz, the obstacle heart yearn contact resistance scope that adapts to is in 0～2K Ω, different model only circuit structure, casing structure and additional function is variant, with regard to the key property of its detecting obstacles, changes little.The anti-interference cable fault detector of GK-1 type height that occurred afterwards, the detectable signal frequency of oscillator output is brought up to 825 hertz, receiver adopts integrated circuit, anti-50 hertz of industrial frequencies and higher hamonic wave interference capability thereof have been improved, but the scope of its adjustment disorder heart yearn contact resistance is still in 0～2K Ω, in fact because of the raising of detectable signal frequency, its scope that adapts to contact resistance also slightly reduces.

The weak point of above-mentioned well known device is: the contact resistance between the cable obstacle heart yearn must be in 2K Ω, could survey effectively the obstacle position, surpass 2K Ω and just be difficult to identification, this is because the detectable signal frequency that above-mentioned detection instrument is exported is higher, it is 400 hertz or 825 hertz, after crossing barrier point, distribution parameter between heart yearn (mainly being distributed capacitance) will constitute certain loop to this detectable signal, form shunting, after the barrier point, still have the detectable signal of suitable intensity, make it be difficult to identification, the applicable situation that this has just limited this quasi-instrument greatly makes the usefulness of its detecting obstacles be subjected to remarkable restriction.

When obstacle heart yearn contact resistance surpassed 2K Ω, above-mentioned existing device must adopt remedial measures and could be suitable for, and its means to save the situation is to adopt high-voltage breakdown obstacle heart yearn, makes the obstacle position form dead short circuit, and contact resistance is zero.This existing approved product of device of remedying, promptly QXZ-03 type cable obstacle punctures device.But using this method is not absolutely can puncture yet, particularly when cable longer, the heart yearn loop resitance greatly the time with regard to the more difficult effect of gathering, moreover this device need be used AC power, its volume, weight, price are all considerably beyond cable fault locator itself, and be both inconvenient, also do not change calculation.

The purpose of this utility model is to avoid the weak point of above-mentioned existing device, and propose that a kind of employing is integrated, high stable, high-resolution circuit structure, by reducing the detectable signal frequency significantly and adopting companding measure, the scope of exaptation obstacle heart yearn contact resistance significantly, improve the cable fault detector that the cable obstacle fixed point is surveyed usefulness.

The purpose of this utility model can adopt following structure and principle to realize:

Adopted the quartz resonator of high stability in the utility model oscillator, behind the high magnification frequency division, again through the filtering frequency selection circuit, just obtained very stable and ultralow frequency sinusoidal signal accurately, after power amplification and boosting, it is right to deliver to barrier line.Wherein frequency dividing circuit is multistage IC frequency division, and frequency selection circuit is the RC active band-pass filter, in addition, is easy to identification for saving electric energy and detectable signal, also is provided with interrupted oscillation circuit and LED in the oscillator and shows.The acquisition of ultralow frequency detectable signal also can adopt square-wave oscillator to add frequency selection circuit formation or employing Wien-bridge oscillator or function generator, but these circuit need be used high stability RC element.Adopt the purpose of above-mentioned measure to be to reduce significantly the detectable signal frequency and promptly reduce the oscillator output signal frequency, make it in the ultralow frequency scope below 50 hertz, because the shunting action of distribution parameter is the function of signal frequency between heart yearn, reduce the detectable signal frequency significantly, just significantly weakened between heart yearn distribution parameter to the shunting action of detectable signal, in other words to the detectable signal of lower frequency, distribution parameter has presented higher impedance, also just correspondingly given prominence to flow through " short circuit " effect of obstacle heart yearn contact resistance of detectable signal, thereby the scope of the utility model adjustment disorder heart yearn contact resistance is expanded, its Standard resistance range expands to 0～20K Ω from 0～2K Ω.

Adopted complex structure in the receiver, by the high-performance that a plurality of amplifier filtering circuits are formed, the ellipse garden of high-order biquadratic function bandpass filter has realized strong inhibition that 50 hertz of industrial frequencies and higher hamonic wave thereof are disturbed and to the accurate frequency-selecting of detectable signal.Receiver partly is provided with the expansion circuit of being made up of resistance switch and amplifier at the second order active band-pass filter, also be provided with and the compressor circuit of expanding the circuit adjusted in concert at its end, low level and high level section to institute's detectable signal have carried out compression and divergence process respectively, to increase the difference of barrier point front and back, the variation of receiver amplitude output signal, this also makes the scope of the utility model adjustment disorder heart yearn contact resistance be expanded.Expansion and compression are to realize by the switch in its circuit respectively, and the switch of two circuit links.In addition, the expansion circuit also can be located at the output terminal of second-order bandpass filter except that the input end that is located at second-order bandpass filter, and an available potentiometer replaces discrete resistor.

The receiver output signal is handled easily except that can quantitatively showing by the indicating circuit gauge outfit, also sent audible signal.Because detectable signal is a ultralow frequency, inconvenience is directly monitored, be provided with one 600 hertz audio signal source for this reason, the sound signal of its output is sent into earphone after amplifying, this signal amplitude is controlled by the DC component of the ultralow frequency detectable signal that receives, thereby the signal amplitude in the earphone has reflected the amplitude of the ultra-low frequency signal that receives indirectly.

Detectable signal is sent into the low noise input stage and is amplified after the induction of receiver probe, amplifying signal improves gain to the further frequency-selecting of second order active band-pass filter after the accurate frequency-selecting of high-order active band-pass filter, and signal amplitude expanded adjusting, its output signal is through the rectification circuit voltage multiplying rectifier, Shu Chu DC component one tunnel is sent indicating circuit thus, and carry out compression adjustment by compressor circuit, further expand adjustment disorder heart yearn contact resistance scope, another road feed signals amplitude monitoring circuit is monitored.

Compared with the prior art the utility model has following advantage:

Reduce the detectable signal frequency by adopting, make it in the ultralow frequency scope below 50 hertz, measure with the compand signal amplitude, the scope of the utility model adjustment disorder heart yearn contact resistance, expand to 0～20K Ω from 0～2K Ω of prior art, improved ability and efficient that cable obstacle is surveyed significantly, and operation is the same with prior art convenient and simple, simultaneously, this instrument adopts fully integratedization, high stable, high-resolution circuit structure, makes complete machine have higher performance.

The utility model Figure of description is as follows:

Accompanying drawing 1. the utility model pierce circuit figure (embodiment one).

Accompanying drawing 2. the utility model acceptor circuit figure (embodiment one).

Accompanying drawing 3. the utility model oscillator frequency dividing circuit figure.

The active band of accompanying drawing 4. the utility model receiver high-orders leads to the current filter circuit diagram.

Accompanying drawing 5. the utility model square-wave oscillators and frequency selection circuit figure (embodiment two).

Accompanying drawing 6. the utility model Wien-bridge oscillator circuit diagrams (embodiment three).

Accompanying drawing 7. the utility model oscillator function generator circuit diagrams (embodiment four).

Accompanying drawing 8. the utility model receiver second order active band-pass filters and expansion circuit diagram (embodiment five).

The utility model will be described in further detail below in conjunction with the accompanying drawings:

Embodiment one.

One, pierce circuit

See accompanying drawing 1. power switch K ₁After the closure, circuit enters duty.By not gate F ₁F ₂And capacitance-resistance R ₁C ₁Export 480 kilohertz signal with the high stable crystal oscillator signal source (2) that quartz-crystal resonator JT forms, through not gate F ₃After the buffering shaping, send into frequency dividing circuit (3), see accompanying drawing 3, frequency dividing circuit is an IC level Four frequency division, divide ratio IC ₁, IC ₂Be 10, IC ₃Be 5, its model is CD4017; IC ₄Be 32, its model is CD4024.Total frequency division coefficient is 16000.Frequency dividing circuit (3) is output as 30 hertz of square waves, by capacitance-resistance R ₃C ₂After the pre-service, be the approximate triangular wave that high-order component greatly reduces, deliver to frequency selection circuit (4) then, frequency selection circuit is the RC active band-pass filter, i.e. the second order bandpass filter that infinitely gains is by amplifier A ₁Resistance R ₄～R ₆Capacitor C ₃C ₄Constitute, it is output as the good and 30 hertz of very precise and stable ultralow frequency sine waves of frequency of waveform, and above-mentioned three parts promptly constitute the ultra-low frequency signal source (1) of this machine.Through C ₅Lotus root is bonded to amplifier A ₂Amplify R ₈R ₇Decision A ₂Gain, output is through RW ₁Adjusting is by C ₆Lotus root is bonded to penultimate stage BG ₁Base stage is amplified, R ₉R ₁₀Be direct current biasing resistance, BG ₁Signal after the amplification is by recommending input transformer B ₁Secondary coil is delivered to final stage power amplifier pipe BG respectively ₂, BG ₃Ground level carries out power amplification.Final stage is operated in the Class B state, by R ₁₁R ₁₂The biasing resistor decision, the final stage signal power is through transformer B ₂Output after boosting, C ₇For improving the amplifier tube nonlinear distortion, the filtering clutter is used.Be the different contact resistance resistance of adjustment disorder heart yearn, the alternating electromagnetic field that loop current is formed reaches the desired strength range of receiver, B ₂Secondaryly be provided with a plurality of taps, by K switch ₂Select, at last by terminal J ₁, J ₂It is right to insert the cable obstacle line.Be connected across the alternating voltage gauge outfit V on the output line ₁Show amplitude output signal, resistance R ₁₃Can determine voltage table V ₁Sensitivity.

Signal is easy to identification and saves power consumption when surveying for making, and the detectable signal of oscillator output adopts interrupted mode, thereby has designed the interrupted oscillation control circuit, and this circuit is by interrupted oscillation source (6), not gate F ₆, diode D ₁And current switch (7) composition, interrupted oscillation source (6) are by not gate F ₄F ₅And capacitance-resistance R ₁₅C ₈Constitute, the realization of interrupted function is to be controlled by very low-frequency square-wave signal that interrupted oscillation source (6) produces, and this square-wave signal cycle is about 2 seconds, by R ₁₅C ₈Parameter is determined, through not gate F ₆Buffering output, the intermittent controlled principle is as follows:

As not gate F ₆When being high level, output terminal (continues about 1 second), at this moment diode D ₁Cut and end, through not gate F ₃480 kilo hertzs of crystal oscillator signals of output can successfully enter frequency dividing circuit (3), and simultaneously, current switch (7) is closed because of its control end obtains high level, TWH8778 class switch I C for example, and power amplifier level direct supply adds, beginning operate as normal, transformer B ₂Export 30 hertz of detectable signals.

As not gate F ₆When output terminal is low level (about 1 second of duration), the input end of frequency dividing circuit (3) is by diode D ₁Clamper is to low level, make the no input pulse signal of frequency dividing circuit (3) during this, the signal that is crystal oscillating circuit (2) can't get into frequency dividing circuit (3), so just there is not signal output yet, current switch (7) will turn-off because of its control end is in low level simultaneously, power amplifier level direct supply is cut off, and quiescent current does not have yet, and makes power consumption more economize.Resistance R ₂Effect, be not gate F during this ₃Be output as pulse high level during moment, restriction D ₁Clamp current, protection not gate F ₃F ₆Nonoverload.

LED shows that (8) can show power amplifier utmost point power supply status, and it will be glittering along with the break-make of current switch (7), R ₁₄Current-limiting resistance for LED.

Two, acceptor circuit:

In the accompanying drawing 2, K ₅K ₆The interlock closed circuit enters duty.L in the probe (9) ₁Be the coil on soft magnetic material, along the alternating electromagnetic field (mainly being magnetic field) of cable reception detectable signal, C ₉But the high fdrequency component of filtering part interference wave, signal is through C ₁₀Lotus root is bonded to high impedance, low noise preamplifier state (10), and this amplifier stage is by amplifier A ₃, resistance R ₁₆R ₁₇Constitute R ₁₇With R ₁₆Ratio determine its gain.Output signal is through amplifier A ₄Buffer compartment from after send into high-order active band-pass filter (11), see accompanying drawing 4, its circuit structure is the very high ellipse garden of the six rank biquadratics function bandpass filter of performance, constitutes amplifier A by identic three joint amplifier filtering circuits ₅, A ₆, A ₇, capacitor C ₁₁C ₁₂, resistance R ₁₈～R ₂₅Form first segment (12); Amplifier A ₈～A ₁₀, capacitor C ₁₃, C ₁₄, resistance R ₂₆～R ₃₃Form second joint (13); Amplifier A ₁₁～A ₁₃, capacitor C ₁₅C ₁₆Resistance R ₃₄～R ₄₁Form the 3rd joint (14).Receiver is to the accurate frequency-selecting of 30 hertz of detectable signals, and the strong inhibition decay that 50 hertz of industrial frequencies and higher hamonic wave are disturbed, and mainly wave filter is finished thus, and suitable gain also is provided simultaneously.

Wave filter (11) output signal is through amplifier A ₁₄The buffering back is by C ₁₇Lotus root is bonded to second order biquadratic active band-pass filter (15), and this wave filter is by amplifier A ₁₅～A ₁₇, capacitor C ₁₈, C ₁₉And resistance R ₄₂～R ₅₀Constitute, its input end is provided with by amplifier A ₁₅, feedback resistance R ₄₆, the expansion resistance R ₄₂～R ₄₅K switch ₃The expansion circuit (16) that constitutes.This wave filter (15) to the expansion of detectable signal amplitude, is also finished at this except further frequency-selecting and raising gain, because of the gain of wave filter can be expanded K in the circuit (16) on a large scale ₃The resistance control of selected connecting resistance, actual is feedback resistance R ₄₆With K ₃K is worked as in the ratio decision of the actual expansion resistance that inserts ₃When " 0 " gear, wave filter (15) gain is minimum, the normal gain when promptly not having expansion; K ₃When choosing connects " 1 " " 2 " " 3 " gear respectively, the resistance value that inserts in the expansion circuit (16) will reduce gradually, and wave filter (15) gain strengthens gradually, with respect to K ₃During the reset gear, mean signal amplitude has been expanded.

Wave filter (15) output signal is through amplifier A ₁₈Buffering is delivered to voltage doubling rectifing circuit (17), and this circuit is by diode D ₂D ₃, capacitor C ₂₀C ₂₁Form C ₂₁Filtering also keeps DC component, A ₁₉Buffering output.Because 30 hertz of detectable signals are by interrupted variation of 2 second cycle, for making amplifier A ₁₉Output DC component also changes (voltage table V by this cycle ₂Then periodic oscillations).C ₂₁Capacity and amplifier A ₁₉The discharge time constant that input impedance constituted should be controlled at 200～300 milliseconds.Two-way output is divided in this DC component buffering back.

One the tunnel enters indicating circuit (18), through diode D ₄, trimmer potentiometer RW ₂Give voltmeter head V ₂Indicator signal amplitude size, compressor circuit (19) compresses processing to detectable signal low level section, and compressor circuit (19) is by compression trimmer potentiometer RW ₃And compression resistance R ₅₁～R ₅₄And K switch ₄Constitute, compressed value is by compression resistance R ₅₁～R ₅₄And potentiometer RW ₃With the dividing potential drop ratio decision of electric power loop, by K switch ₄Regulate, work as K ₄When being in " 0 " gear, do not have compression, work as K ₄When placing other gears, because of there is one in corresponding gear end by power branch, i.e. R ₅₁～R ₅₄The compression voltage of determining that branch road forms is (with respect to power supply electronegative potential V _EE), at this moment only as amplifier A ₁₉When output voltage is higher than this voltage, voltage table V ₂Indication is just arranged, and (signal amplitude is poor with compression voltage, in fact D ₄Also to consume a point voltage), be lower than the signal of this voltage, voltage table does not all have indication, means to reduce.K ₄Institute's connecting terminal is number big more, and decrement is also big more.RW ₃Can compress fine setting.In compressive state, work as A ₁₉When output end voltage is zero or low amplitude signal,, be provided with diode D for making the voltage table indicator nonreversible ₄RW ₂The adjustable voltage Table V ₂Sensitivity, also play simultaneously expansion fine setting effect.

Signal amplitude monitoring circuit (20) is delivered on another road, and this circuit is made up of audio signal source (21) and volume control circuit (22) and earphone T.600 hertz of volume control circuits (22) are between 600 joseph audio signal sources (21) and earphone T, and the sound signal that is produced by signal source (21) is through R ₅₇Suitably decay, C ₂₄Send into volume control circuit (22) after lotus root is closed, audio signal source (21) is simplified by the second order bandpass filter that infinitely gains, by amplifier A ₂₀, capacitance-resistance R ₅₅, R ₅₆, C ₂₂, C ₂₃Form; Volume control circuit (22) is by transistor BG ₄, BG ₅, resistance R ₅₈～R ₆₁Form BG ₄Be 600 hertz of signal flows being produced of signal source (21) to the earphone T must through amplifier tube, BG ₅Play on-off action, BG ₄, BG ₅Base stage respectively through R ₅₈, R ₅₉, be controlled by from A ₁₉DC component after the detectable signal rectification of output terminal, i.e. amplifier A ₁₉When output voltage is high, BG ₄The working point raises, BG ₅Be tending towards saturated, 600 hertz of signals among the earphone T are strong like this, on the contrary BG ₄The working point descends, BG ₅Be tending towards cutting and end, 600 hertz of signals among the earphone T just a little less than, also just 30H ₂600 hertz of signal amplitudes that the changes in amplitude of detectable signal is converted in the earphone change, because A ₁₉The DC component of output changes by detectable signal is interrupted, so the 600 joseph audio signals of hearing among the earphone T also are interrupted the variations.After this function was arranged, generalized case need not be seen the voltage table indication, when needs are accurately judged, just sees gauge outfit, is convenient to operation.

Be handled easily, the K of expansion and compressor circuit ₃, K ₄Interlock makes circuit become synchronous regulating circuit, does not have the corresponding nothing compression of expansion, the corresponding little compression of little expansion, the corresponding compression greatly of big expansion.

After adopting the companding measure, can increase the difference that the receiver output signal changes before and after the barrier point, illustrate down: bigger as a certain cable obstacle heart yearn contact resistance, during no companding, i.e. K ₃, K ₄All in zero-span, if the receiver output signal is 2.0V before the barrier point, cross barrier point after, receiver output also has 1.5V.At this moment, expand 2 times and promptly become 6.0V and 4.5V, reduce 4.0V again simultaneously, just become 2.0V and 0.5V at last.Just with the amplitude ratio of receiver output signal before and after the barrier point, the 2:1.5 during by no companding becomes the 2:0.5 behind the companding for this, and the latter's difference is certain remarkable, means so has made the expanded range of the utility model adjustment disorder heart yearn contact resistance.

Embodiment two

See accompanying drawing 5, ultra-low frequency signal source (1) also can adopt square-wave oscillator (25) and frequency selection circuit (4) to constitute not gate F in the oscillator ₁₀, F ₁₁And capacitance-resistance R ₈₀C ₃₀Constitute square-wave oscillator (25), its frequency is by capacitance-resistance R ₈₀C ₃₀Parameter is determined, by regulating its parameter, can be made it to produce the ultralow frequency square wave of requirement.Output is through not gate F ₁₂Buffer compartment from, by capacitance-resistance R ₃C ₂Pre-service becomes the less approximate triangular wave of high-order component, sends into frequency selection circuit (4) again and selects first-harmonic.Frequency selection circuit output is the good ultralow frequency sine wave of waveform, and all the other each several part circuit structures of the structure of frequency selection circuit (4) and oscillator and principle of work are identical with embodiment one, only diode D ₁The branch road cancellation.

Embodiment three

See accompanying drawing 6, oscillator ultra-low frequency signal source (1) also can be replaced by Wien-bridge oscillator (26), and it is by amplifier A ₃₀, Wien bridge circuit (27), current potential RW ₁₀, resistance R ₈₁And thermistor RT constitutes.Oscillation frequency is by the R in the Wien bridge circuit ₈₂, R ₈₃, C ₃₁, C ₃₂Parameter decision.R ₈₁Be feedback resistance, thermistor RT amplitude limit, RW ₁₀Waveform is adjusted.All the other each several part structures of oscillator and principle be with embodiment one, only diode D ₁The branch road cancellation.

Embodiment four

See accompanying drawing 7, oscillator ultra-low frequency signal source (1) also can be replaced by function generator (28), and it is integrated Waveform Generator, and present embodiment adopts the ICL8038 type, only uses sine wave, by terminal 2 outputs.Frequency is by C ₃₃, RW ₁₁, RW ₁₂The three element parameter is determined.RW ₁₁, RW ₁₂Except that the scalable frequency, also regulate the symmetry of waveform.。R ₈₄Improve waveform, R ₈₅Pull-up resistor for IC.The oscillator remainder is identical with embodiment one, only diode D ₁The branch road cancellation.

Embodiment five.

See accompanying drawing 8.Receiver expansion circuit also can place the output terminal of second order active band-pass filter, as (29) among Fig. 8.Its wave filter (30) gain is fixing (because of R ₄₆With R ₆₂Ratio fix), output signal be connected to the expansion circuit (31), the expansion circuit (31) by the resistance R that is in series ₄₂～R ₄₅And selector switch K ₃Constitute.Filter output signal is divided into several amplitude class thus.K ₃Do not have expansion during the reset gear, amplitude output signal is normal, works as K ₃When putting other gears, output amplitude promptly increases a corresponding numerical value, means the signal amplitude expansion.K ₃Gear is high more, expand also big more because K ₃, K ₄Interlock, this moment, compression was also big more, and all the other each several part circuit of receiver and principle of work are identical with embodiment one.R in its expansion circuit (31) ₄₂～R ₄₅And K ₃Also can be replaced by potentiometer, this moment, expansion amount can be regulated continuously, and no longer with K ₄Interlock.

In addition, the circuit construction variations of oscillator and receiver can make up mutually, and multiple mode is arranged.

Claims (11)

1, a kind of cable fault detector is made up of oscillator and receiver two parts, and oscillator is made up of ultra-low frequency signal source (1), amplifying circuit (5) and interrupted oscillation control circuit and power supply; Receiver is made up of probe (9), low noise input stage (10), frequency selection circuit (11) (15), rectification circuit (17), indicating circuit (18), signal amplitude monitoring circuit (20) and power supply, it is characterized in that:

Ultra-low frequency signal source (1) adopts crystal oscillation source (2), digital divider circuit (3) and frequency selection circuit (4) to constitute; Or adopt square-wave oscillator (25) and frequency selection circuit (4) to constitute; Again or adopt Wien-bridge oscillator (26), or function generator (28), the interrupted oscillation control circuit is by interrupted oscillation source (6), not gate F ₆, diode D ₁And current switch (7) composition, in addition, oscillator section also is provided with LED and shows (8),

The receiver frequency selection circuit comprises high-order active band-pass filter (11) and second order active band-pass filter (15) two parts; Signal amplitude monitoring circuit (20) is made up of audio signal source (21) and volume control circuit (22) and earphone T; Indicating circuit is provided with trimmer potentiometer RW in (18) ₂, in addition, the receiver final stage is provided with compressor circuit (19).

2, detection instrument according to claim 1 is characterized in that oscillator digital frequency dividing circuit (3) is multistage IC frequency division, and frequency selection circuit (4) is the RC active band-pass filter.

3, detection instrument according to claim 1, the high frequency high stable signal that it is characterized in that oscillator crystal oscillation source (2) generation is through not gate F ₃After the buffering shaping, send into digital divider circuit (3) frequency reducing, by capacitance-resistance R ₃C ₂Pre-service, enter frequency selection circuit (4) frequency-selecting, the sinusoidal ultra-low frequency signal after the frequency-selecting enters amplifying circuit (5) and amplifies, and by transformer B ₂Send into the obstacle cable after boosting.

4, detection instrument according to claim 1 is characterized in that receiver high-order active band-pass filter (11) saves the amplifier filtering circuits by identic three and forms.

5, detection instrument according to claim 1 is characterized in that being provided with in the receiver second order active band-pass filter (15) an expansion circuit (16), and this circuit is by amplifier A ₁₅, the expansion resistance R ₄₂～R ₄₅, feedback resistance R ₄₆And K switch ₃Form, and expansion resistance is arranged on the input end of wave filter.

6, detection instrument according to claim 1 is characterized in that also can will expanding the output terminal that circuit (31) be arranged on receiver second order active band-pass filter (30), and this expansion circuit is only by the expansion resistance R ₄₂～R ₄₅And K switch ₃Form, perhaps adopt a potentiometer to get final product.

7, detection instrument according to claim 1 is characterized in that compressor circuit (19) is by resistance R ₅₁～R ₅₄, compression trimmer potentiometer RW ₃And K switch ₄Form.

8,, it is characterized in that expanding circuit (16) and compressor circuit (19) is a synchronous regulating circuit, by K switch according to claim 5 and 7 described detection instruments ₃K ₄Interlock realizes.

9,, it is characterized in that the expansion amplitude is by feedback resistance R according to claim 5 and 7 described detection instruments ₄₆With the expansion resistance R ₄₂～R ₄₅Ratio decision, by K switch ₃Regulate; Compressed value is by compression resistance R ₅₁～R ₅₄And potentiometer RW ₃With the dividing potential drop ratio decision of electric power loop, by K switch ₄Regulate.

10, detection instrument according to claim 1, it is characterized in that the cable detection signal through the probe (9) induction by C ₁₀Lotus root is closed and sends into low noise input stage (10) amplification, and amplifying signal is through amplifier A ₄Buffer compartment is from sending into high-order active band-pass filter (11) frequency-selecting, and its output signal is through amplifier A ₁₄The buffering back is by C ₁₇Lotus root is bonded to second order active band-pass filter (15), and further frequency-selecting improves gain, and signal amplitude is expanded adjusting, and then, output signal is through A ₁₈Buffering is delivered to rectification circuit (17), and Shu Chu DC component one tunnel is sent the indication of indicating circuit gauge outfit thus, and passes through K by compressor circuit (19) ₄Carry out compression adjustment; Another road feed signals amplitude monitoring circuit (20) is monitored.

11, according to claim 1 and 10 described detection instruments, the 600 joseph audio signals that it is characterized in that being produced by audio signal source (21) are through R ₅₇Suitably decay, C ₂₄After closing, lotus root sends into volume control circuit (22), by amplifier A ₁₉DC component after the detectable signal rectification of output is through amplifier tube BG ₄With switching tube BG ₅Control is by C ₂₅Lotus root is bonded to earphone T and monitors.

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