JPH0783299B2 - Signal detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a capacitively coupled signal detector that detects a signal without directly connecting to a communication line that is a monitoring target line.

[Conventional technology]

Conventionally, when observing a voltage or current waveform flowing in a communication line or power line, which is a monitored line, without contacting a conductor, the line to be observed such as a communication line is electromagnetically coupled with a toroidal coil to form a current waveform. A method of taking out a voltage waveform by taking out or observing a wire by sandwiching it with a metal electrode from above the coating of the wire and performing electrostatic coupling is adopted. In particular, when observing a signal flowing through a communication line, it is necessary to ensure that it does not affect the transmission characteristics. Either electromagnetic coupling or electrostatic coupling should be as weak as possible at the observation point. Care must be taken to prevent signal loss and non-uniformity of impedance on the communication line.

Conventionally, when a signal flowing through a communication line is detected without contact, 2
A pair of communication lines are sandwiched between electrodes from the outer sheath of the core wire by a book, and a signal is extracted by electrostatic coupling, which is amplified and detected by a high input impedance differential amplifier. FIG. 4 is a conceptual diagram of the electrostatic coupling system, and FIG. 5 is an equivalent circuit of FIG.
In Fig. 5 (a), the coupling capacitance between the communication line and the electrode is 2C,
This is a balanced-type equivalent circuit when the load resistance to ground including the input impedance of the high input impedance differential amplifier is R / 2. FIG. 5 (b) is an unbalanced equivalent circuit which is completely equivalent to FIG. 5 (a). Therefore, the impedance of the detection system composed of C and R is extremely large compared to the characteristic impedance ρ of the communication line, and ρ can be almost ignored. Therefore, assuming that the voltage of the signal source is E _S and the detection voltage of the signal detector is V _I , it is obvious that the voltage attenuation amount 20Log (E _S / V _I ) is expressed by the following equation.

Voltage Attenuation _{= 20Log (E S / V I} ) = 10Log {(1 + ρ / R) 2 + (1 / ωCR) 2} ≒ 10Log {1+ (1 / ωCR) 2} ...... (ρ«
R) E _S : Voltage of signal source V _I : Detection voltage of signal detector ρ: Characteristic impedance of communication line R: Impedance of detection system C: Coupling capacitance of communication line and electrode ω: Angular frequency (2πf, f : Frequency) [Problems to be Solved by the Invention] That is, FIG. 5 is a simple high-pass filter in which the coupling capacitance C is uncertain due to mechanical contact, and as shown in FIG. The characteristic has a frequency characteristic that greatly fluctuates in the low frequency region. It is physically impossible to increase the coupling capacitance C in the electrostatic coupling method that results in such weak coupling, and it is difficult to secure a band with a flat attenuation characteristic up to a low frequency. Therefore, it has been impossible to faithfully detect and observe a wideband signal waveform such as a digital signal including a low frequency component in a non-contact manner.

The present invention has been made in view of such circumstances.
An object of the present invention is to provide a signal detector that solves the problems caused by weak coupling and that faithfully detects the voltage waveform of a signal flowing through a communication line.

[Means for Solving the Problems]

In the signal detector of the present invention in order to solve the above problems, by positively utilizing the electrode and the capacitance between the ground,
Expands the low-frequency region and faithfully detects wideband signals. That is, a means having a function of generating between the two electrodes a capacitance value that is close to the coupling capacitance generated between the pair of balanced type communication lines that are the monitored lines and the electrodes, specifically, the electrodes Sandwich.

An external capacitance for compensation for band compensation was added.

Further, in claim (2), a means having a function of generating a capacitance value approximate to the coupling capacitance generated between the monitoring target line and the electrode of the unbalanced communication line between the electrode and the pair value, specifically, A compensating core wire is sandwiched between the electrodes.

An external capacitance for compensation for band compensation was added.

[Action]

According to the signal detector configured as described above, the transfer characteristic becomes flat up to a low frequency of about 100 Hz even with weak coupling due to electrostatic capacitance.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the connection of the electrode portion of the present invention. FIG. 1 (a) is a side view of the electrode, FIG. 1 (b) is a structural view seen from the upper surface of the electrode, and FIG. 2 is FIG. Is an equivalent circuit of. Hereinafter, correspondence will be described by indicating the drawing number in the drawing of FIG. 1 by (). The compensating core wire (2) connects the monitored wire (1) to the electrode (3).
The coupling capacitance C _S in an amount equal coupling capacitance C _C that occurs when sandwiched in, is for providing an electrode (3) between ground (6). The additional compensation external capacitance (4) _CE is a capacitance that is fixedly added to further widen the low frequency band.

The equivalent circuit of FIG. 1 is shown in FIG. 2 in unbalanced form as in FIG.

The voltage attenuation amount in FIG. 2 is easily expressed by the following equation.

Voltage attenuation = 20Log (E _S / V _I ) = 10Log {[1+ (ρC _S + R (C _C + C _E )) / RC _S ] ² + [(ω ² C _S (C _C + C _E ) ρR-1) / RωC _S ] ² } ≈ 10Log {[1+ (C _C + C _E ) / C _S ] ² + [1 / RωC _S ] ² }… (ρ≈0) E _S : Signal source voltage V _I : Signal detector Detection voltage ρ: Characteristic impedance of the monitored line R: Impedance of the detection system C _S : Coupling capacitance with the monitored line C _C : Coupling capacitance between the electrode and the compensation core wire to ground C _E : External for compensation Capacitance ω: angular frequency (2πf, f: frequency) FIG. 3 shows the frequency characteristic of the voltage attenuation amount. When the coupling capacitance C _C due to the compensating core wire 2 is added, a flat loss is generated over a high frequency region, but the flat portion spreads to a low frequency band, and a wide band can be achieved. The increase in loss in the flat portion can be sufficiently amplified by a high input impedance differential amplifier (not shown), and the effect of compensation is great. External capacitance for compensation (4) _CE
By adding, it is possible to further expand the flat part in the low frequency range. Usually, the coupling capacitance C _S with the monitored line is several pF or less, and the characteristic impedance ρ of the monitored line is several hundred Ω or less. C _C +
When C _E is made 10 times as large as C _S , the loss in the flat part is increased by about 20 dB, but the frequency band of reduction is expanded by one digit, from 10 kHz to 1 kHz. On the other hand, in a high frequency region by inserting the C _C + C _E, but affect the characteristic impedance of the monitored line ρ loss increases, no problem flat characteristic is obtained to 100MHz about if 10 times the C _S . It is easy to gain high input impedance differential amplifier and 40 dB, the C _C + C _E is C _S
It can be inserted up to about 100 times, and even with weak coupling due to electrostatic capacitance, signals with a low frequency of about 100 Hz can be detected with flat characteristics.

In the present embodiment, an example in which an unbalanced communication line is used as the monitored line has been described, but it goes without saying that the same applies to the balanced communication line.

〔effect〕

As described above, according to the signal detector of the present invention, a capacitance value that is close to the engagement capacitance that occurs between the pair of balanced communication lines that are the lines to be monitored and the electrodes is generated between the two electrodes. A means having a function and an external capacitance for compensation for band compensation are added.

Further, in claim (2), a means having a function of generating a capacitance value approximate to the coupling capacitance generated between the unbalanced communication line which is the monitored line and the electrode between the electrode and the ground, and band compensation. An external capacitance for compensation is added. Therefore, the transfer characteristic becomes flat even at low frequencies.

[Brief description of drawings]

FIG. 1 is a connection diagram of electrode portions showing an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram thereof, FIG. 3 is a frequency characteristic diagram of voltage attenuation amount according to the first embodiment, and FIG. FIG. 5 is a conceptual diagram of a conventional electrostatic coupling system, FIG. 5 is an equivalent circuit diagram thereof, and FIG. 6 is a frequency characteristic diagram of voltage attenuation according to the conventional system. 1 ... Monitored wire, 2 ... Compensation core wire, 3 ... Electrode, 4 ... External capacitance for compensation, 5 ... Load resistance, 6 ... Ground (earth).

Claims (2)

[Claims] 1. A signal detector provided with two electrodes (3) that are electrostatically coupled to a pair of balanced communication lines that are monitored lines (1), and that are coupled by capacitance. A signal obtained by adding a means (2) having a function of generating a capacitance value close to the coupling capacitance generated between the electrodes between the two electrodes and a compensation external capacitance (4) for performing band compensation. Detector. 2. A signal detector provided with an electrode (3) electrostatically coupled to an unbalanced communication line which is a monitoring target line (1), wherein the signal detector is coupled by electrostatic capacitance between the monitoring target line and the electrode. A signal detector having means (2) having a function of generating a capacitance value close to the generated coupling capacitance between the electrode and the ground, and a compensation external capacitance (4) for band compensation.