JPH0566077B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an automatic degaussing method for a color cathode ray tube display device used in a moving and swinging state.

(Prior art and its problems) This type of device, such as a fish finder or a scanning sonar, uses a color cathode ray tube as a display device. Level changes are used to display different colors for each set level range to facilitate recognition and analysis of detected information.

However, color cathode ray tube display devices, which are generally used in a moving and oscillating state, are magnetized by the influence of the earth's magnetism, which causes unnecessary deflection of the electron beam, causing, for example, what should normally be a red display to become a yellow display.
Decreases color purity and makes it difficult to see. Therefore, there is a drawback that the recognition and analysis of the displayed information may be erroneous.

Therefore, conventionally, a color cathode ray tube display device is provided with a demagnetizing coil to demagnetize the display device. However, conventional degaussing has no relation to the series of operations of fish finders, such as transmitting sound waves and receiving reflected waves.
The method used is to do it in proportion to the number of times.

Therefore, in fish finders that read out and display transmitted signals, received reflected signals, etc. once into a memory circuit, demagnetization is performed during the period of time the signal is stored in the memory, and then the signal is demagnetized by applying a degaussing current. It is unavoidable that the generated noise is taken into the memory along with the received reflected signal and the like. For this reason, for example, as shown in the image display example shown in Figure 1,
There is a drawback that a noise image b due to demagnetization is displayed together with a school of fish image a and the like, which may cause the image to be mistaken for a school of fish image.

(Objective of the Invention) The present invention has been made for the purpose of providing an automatic degaussing method for color cathode ray tubes, which eliminates the drawbacks of the conventional methods as described above.

(Means of the present invention for solving the problem) A fish finder, etc. that uses the above-mentioned display method, that is, a method in which the signal to be displayed is temporarily captured in a memory, and then read out, processed as a video signal, and displayed. Generally, as shown in Fig. 2, the transmission and reception of sound waves c and the capture of these signals to be displayed into the memory are carried out during the retrace period _T1 of the vertical scanning line of a cathode ray tube display device, and the captured information is is read out and displayed within the video display period _T2 between the vertical retrace period _T1 and the next retrace period _T1 .

Based on the above, the present invention creates a period _T4 other than the period _T3 during which the signal to be displayed is taken into the memory within the vertical retrace period _T1 as shown in FIG. Alternatively, if the degaussing AC current i is made to flow through the degaussing circuit within the period _T4 at the time interval required for degaussing, it is possible to prevent the noise caused by the input of the degaussing current from being taken into the memory circuit. The idea was to prevent noise from being displayed as an image on a cathode ray tube display. Next, examples of the present invention will be described.

(Embodiment) FIG. 4 is a circuit diagram of an embodiment of the present invention showing an application example of a fish finder. In the figure, 1 is a transducer,
2 is a transceiver, 3 is an analog-to-digital converter, 4
is a CRT controller (controller for a cathode ray tube display device), 5 is a central processing unit, 6 is a RAM (random access memory), 7 is a DMA controller (direct memory access controller),
8 is a DMA request timer, 9 is an image memory device, 10 is a color synthesizer, 11 is a polarizing circuit, 12 is a color cathode ray tube display device, 13 is a degaussing signal output spot, and 14 is a degaussing circuit provided on the cathode ray tube. Next, the operation will be explained.

The central processing unit 5 is controlled by the CRT controller 4 to send out a trigger signal to trigger the transceiver 2, and the output excites the transducer 1 to emit a sound wave into the sea. The reflected waves from the sea are added to the transceiver 2 via the transducer 1, where the transmitted signal and the reflected signals from the school of fish, the seabed, etc.
After being amplified and detected as shown in the figure, the signal is applied to an analog-to-digital converter 3 and converted into a digital signal corresponding to the level.

On the other hand, the central processing unit 5 synchronizes with the supply of the trigger to the transceiver 2 by the CRT controller 4.
A write address signal is sent to the DMA controller 7 in accordance with the sampling clock signal from the DMA request timer 8, and the transmitted signal and received reflection within the measurement distance are digitized by the analog-to-digital converter 3. Signals and the like are captured and stored in the RAM 6, and further transferred to the image memory device 9 in response to signals from the central processing unit 5. When the above operations are completed, the CRT controller 4 applies a trigger output to the demagnetizing output port 13, thereby causing a demagnetizing alternating current to flow through the demagnetizing circuit 14, thereby demagnetizing the cathode ray tube 12.

When degaussing is completed, the stored contents of the image memory device 9 are read out in synchronization with the sweeping of the cathode ray tube display device 12 by the deflection circuit 11 in response to a signal from the CRT controller 4, and this is combined into a video signal by the color synthesizer 10. and is displayed on the cathode ray tube display device 12.

(Effects of the Invention) As described above, in the present invention, since the cathode ray tube is demagnetized while avoiding the period during which the detection information signal is stored in the memory, the noise caused by the degaussing is displayed on the cathode ray tube display device along with the detection information signal. There is no. Therefore, there is no risk of mistaking a noise image for a necessary video.

Although the present invention has been explained above using fish finders and scanning sonar as examples, it can also be applied to automatic degaussing of devices that capture signals to be displayed into a memory, retrieve them, and display images on a color cathode ray tube display device. Needless to say.

[Brief explanation of the drawing]

FIG. 1 is an example of a cathode ray tube display using a conventional degaussing method, FIGS. 2 and 3 are diagrams explaining the principle of the present invention, and FIG. 4 is a diagram of an embodiment of the present invention.

Claims (1)

[Claims] 1. In a device using a color cathode ray tube display device, which captures the information signal to be displayed into the memory during the vertical blanking period, and reads out and displays the captured contents of the memory during the video display period, the information signal is not displayed during the vertical blanking period. A method for degaussing a color cathode ray tube, characterized in that degaussing is performed by providing a degaussing period following a signal memory acquisition period.