JPH02288792A - Fault discriminating method for transmission line in cctv system - Google Patents

Abstract

PURPOSE:To discriminate the fault cause of a CCTV system in a monitoring device side and to improve efficiency for work such as maintenance, etc., by detecting a change in the input impedance of the monitoring device and discriminating the fault of a transmission line according to the change of the input impedance. CONSTITUTION:When a coaxial cable 3 is not interrupted or interrupted, an input impedance R of a monitoring device 4 is changed only by R2-R1XR2/(R1+ R2). In a voltage drop level (E0) discriminating circuit 5c, it is discriminated whether an input voltage corresponds to E01 and E02 levels or not. When the level of the input voltage corresponds to the E02 level, it is judged that the fault and interruption are generated in the coaxial cable 3. Then, a message, etc., showing such a condition is displayed in a fault display discriminating circuit 5d. Accordingly, it can be easily discriminated by whichever the coaxial cable of the CCTV system or a CCTV camera 1 the fault is caused.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to CCTV (C1osed C1rcuit).
CCD (charge coupled dev) used in cameras, video cameras, etc.
The present invention relates to a method for determining a failure in a transmission path (coaxial cable) in a CCTV system, for example, a break in a transmission path (coaxial cable) for transmitting video signals from a camera to a monitor device.

[Conventional example] In recent years, CGTV cameras and video cameras have become smaller, lighter,
CCO solid-state image sensors are used because of their high reliability. CGTV cameras (CC cameras) are not only used in security systems at financial institutions and convenience stores, but have also come to be used in the FA field, such as visual sensors for robots.

By the way, as shown in FIG. 5, the camera 1 and the monitor device 2 of the CGTV system are connected by a transmission path (coaxial cable) 3, and the video signal of the camera 1 is transmitted to the monitor device via the coaxial cable 3. 2. At this time, it is assumed that a failure occurs in the CCTV system and the image from the camera 1 is no longer displayed on the monitor device 2.

It is assumed that there is a raster on the screen of the monitor device 2, that is, the monitor device 2 is not out of order.

In this case, the procedure for investigating the cause of the failure is to check for the presence or absence of a video signal according to the following procedure.

(1) If end A: no video signal and end B: video signal present, it can be determined that the coaxial cable 3 is the cause of the failure.

(2) If end A: no video signal and end B: no video signal, it can be determined that the camera 1 is the cause of the failure.

In this way, by detecting the presence or absence of a video signal at each location of the CCTV system, the location of the failure can be determined.

[Problems to be Solved by the Invention] However, in the above CCRV system, since the CCTV camera is usually installed at a high place, it is difficult to confirm the presence or absence of a video signal at end B, and the
cTv cameras are sometimes installed in dangerous locations, which not only requires time and effort, but also poses a safety problem.

This invention was made in view of the above-mentioned problems, and its purpose is to enable the monitoring device to identify failures in the transmission path and to facilitate and safely investigate the cause. An object of the present invention is to provide a method for determining a failure in a transmission path in a CCTV system.

[Means for Solving the Problem] In order to achieve the above object, the present invention transmits a video signal output from a camera to a monitor device via a transmission path, and displays the image taken by the camera on the screen of the monitor device. In a CCTV system that displays captured images, a change in the human input impedance of the monitor device is detected, and a failure of the transmission path is determined based on the change in input impedance.

[Operation] Since the method described above is adopted, if a failure occurs in the transmission path (coaxial cable), for example, a disconnection occurs, the human power impedance of the monitor device becomes large. That is, this is because the output impedance of the camera is not parallel to the input impedance of the monitor device. The change in the human power impedance is obtained on the monitor device side, and a break in the transmission path is determined by converting the human power impedance.

Therefore, a monitor device outputs a signal of a predetermined voltage (E) to the transmission path, and detects the voltage drop level (Eo) of the resistance of the human input impedance due to this voltage. Then, since the level (Eo) is different when the transmission path is normal and when it is disconnected, the above-mentioned failure of the transmission path is determined based on the detection level.

[Example] Hereinafter, an example of the present invention will be described based on FIGS. 1 to 4. In the figure, the same or corresponding parts as in FIG. 5 are denoted by the same reference numerals, and redundant explanation will be omitted.

1 and 2, the monitor device 4 includes a fifth
In addition to the functions of the monitor device 2 shown in the figure, the 0 discriminating circuit 5 is equipped with a discriminating circuit 5 that detects changes in the impedance of the coaxial cable 3 and determines a failure of the coaxial cable 3. An oscillation circuit 5a that generates a signal (for example, a rectangular wave, a triangular wave signal, etc.), a resistor (Rs) sb for supplying the signal to the coaxial cable 3, and a voltage drop level due to the input impedance of the monitor device 4 due to the resistor 4a. An E0 level discrimination circuit 5c detects the voltage (E, ) and discriminates a failure of the coaxial cable 3 from this voltage (E, ) level, and a failure discrimination display circuit 5d displays a failure etc. according to the result of this discrimination. It is provided. Note that 1a is CC
This is the resistance (R1) of the output impedance of the camera 1.

Next, the operation of the discriminating circuit having the above configuration will be explained based on the circuit diagrams of FIGS. 3 and 4.

First, it is assumed that a voltage (E) signal is being output from the oscillation circuit 5a. At this time, if the coaxial cable 3 is normal, the input impedance resistance (R,
)4a, the voltage drop level (E, ) is expressed by the following equation (a) using the circuit shown in FIG.

R1//R2/(Rs + R1//R2) =Eox
-(a) If the coaxial cable 3 has a fault, for example, a break, the voltage drop level (Eo) will be expressed by the following equation (b) using the circuit shown in FIG.

R, / (R, + Rx) = Eom<<Eo□)-...
-Cb) That is, the input impedance (R) of the monitor device 4 is divided into (R2-kl//R,) when the coaxial cable 3 is not disconnected and when it is disconnected.

Note that Rx//x<, as described above, is RxRz/(R□+
Rz).

Then, due to the operation of the oscillation circuit 5a, the input voltages Eo, , l!
:, It is determined whether the level corresponds to the level.

If the input voltage level corresponds to Eol, it is determined that no failure has occurred in the coaxial cable 3, and the failure determination display circuit 5d displays a message or the like to that effect. Also, the level of the input voltage is E. If it corresponds to 2, it is determined that a failure or disconnection has occurred in the coaxial cable 3, and a message or the like to that effect is displayed by the failure display determination circuit 5d. The display by the failure display discriminating circuit 5d may be, for example, displaying various messages on the screen of the monitor device 4.

In this way, since a failure of the coaxial cable 3 can be easily determined on the monitor device 4 side, the presence or absence of a video signal at both ends A and B of the coaxial cable 3 (shown in FIGS. 1 and 2) It becomes possible to easily determine whether the cause is caused by the coaxial cable of the CCRV system or the CCTV camera 1 without checking, and it is possible to improve work efficiency such as maintenance.

[Effects of the Invention] As explained above, according to the method for determining failure of a transmission path in a CCTV system of the present invention, failure of a transmission path (coaxial cable) between a CCTV camera and a monitor device, such as a disconnection, can be detected by inputting the input signal to the monitor device. Since the detection is based on changes in impedance, the monitor device can determine if there is a failure in the coaxial cable, and the cause of the failure in the CCTV system is the CCTV camera.

The monitor device can determine which coaxial cable is causing the problem, which improves work efficiency such as maintenance.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1 and 2 show an embodiment of the present invention, and CG
A schematic block diagram of a CCTV system to which the method for determining failure of a transmission path in a TV system is applied; FIGS. 3 and 4 are circuit diagrams for explaining the human power impedance of the monitor device in the CCTV system; FIG. 1 is a schematic block diagram of a conventional CCTV system; FIG. In the figure, 1 is the CCTV camera, 1a is the output impedance resistance (R,: of CCTV camera 1), 2 and 4 are the monitor device, 3 is the transmission path (coaxial cable), and 4a is the output impedance resistance (R2: monitor ), 5 is a discrimination circuit, 5a is an oscillation circuit, 5b is a resistor (R1), and 5c is an E
0 level discrimination circuit, 5d is a failure discrimination display circuit. Figure 3 Figure 4

Claims (2)

[Claims] (1) In a CCTV system that transmits a video signal output from a camera to a monitor device via a transmission path and displays the video captured by the camera on the screen of this monitor device, changes in the input impedance of the monitor device are A CCTV characterized in that a failure of the transmission path is determined based on a change in input impedance.
A method for determining failure of a transmission path in a system. (2) Detection of the input impedance change involves obtaining the voltage drop level due to the resistance of the input impedance of the monitor device when a signal of a predetermined voltage is output to the transmission path via a resistor of a predetermined value, and using this level to obtain the voltage drop level due to the resistance of the input impedance of the monitor device. 2. A method for determining a failure in a transmission path in a CTV system according to claim 1, wherein a failure in the transmission path is determined and a display is made in accordance with the determination.