JPH0497658A - External magnetic field correction device for crt - Google Patents

Abstract

PURPOSE:To correct an outside magnetic field automatically even when the magnetic field enters in any direction by arranging magnetic sensors around a CRT screen and detecting a level difference of output signals of the sensors when the output signals take place simultaneously and generating a correction current while a polarity data is added thereto. CONSTITUTION:Magnetic sensors 51-54 are fitted to four corners of a display screen and output signals are fed to a comparison discrimination circuit 12 via amplifiers(AMP) 101-104 and A/D converters 111-114. Then a signal fed to the comparison discrimination circuit 12 compares and discriminates detection times and levels of the magnetic sensors 51-54. When outputs of the magnetic sensors 51-54 are changed simultaneously, the magnitude and the direction of the acting magnetic field are detected based on the change quantity, the polarity and the changing state and a correction current is generated based on the result of detection. Thus, when the CRT is used under a large outside magnetic field, the distortion of the display screen is automatically corrected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for using a CRT in an environment with a large external magnetic field (for example, an environment where the CRT is used in an electromagnetic crane in a factory, a large electromagnet, a ship equipped with a degaussing device, etc.). The present invention relates to an external magnetic field correction device for a CRT that automatically corrects distortion of a display screen when used.

[Prior Art] A CRT display device displays characters or figures on a CRT screen by deflecting an electron beam. Therefore, when an external magnetic field is applied, the deflection position of the electron beam is disturbed, causing distortion (rotational distortion and distortion in the vertical or horizontal direction of the display screen), and the displayed image is disturbed. For this reason, conventionally, as shown in FIG. 4, a shield case 1 having high magnetic permeability, such as permalloy, was placed around the CRT. However, although this method is effective against the external magnetic field B1 that enters the shield case at right angles, it is defenseless against the external magnetic field B2 that enters the CRT display surface perpendicularly. Therefore, as shown in FIG. 5, a correction coil 2 is attached near the CRT display surface, and an amplifier (AMP) 3 supplies this coil with a current that generates a correction magnetic field Bff so as to cancel the external magnetic field B2. Was. The thickness of the correction magnetic field was adjusted by a volume control 4 provided on the panel surface.

[Problems to be Solved by the Invention] However, in this conventional method, it is necessary to correct the magnetic field using a manual adjuster, so if the operator is busy with other operations, he or she may not have time to make the correction. It is also effective against rotational distortion caused by the external magnetic field B2 entering perpendicularly to the CRT display surface, but it is effective against vertical/horizontal movement of the screen due to the magnetic field B4 entering at a certain angle as shown in the symbol in Figure 5. Less is.

On the other hand, there is also a method of attaching a magnetic sensor to detect and correct the external magnetic field. However, even with this method, there are human problems caused by the operator, for example, when metal objects such as watches and rings are brought close to the magnetic sensor, the magnetic sensor detects the concentration of magnetic flux due to these metals, which may generate unnecessary correction current. There is a problem that the direction of the external magnetic field cannot be detected.

[Means for Solving the Problems] In order to solve the above problems, the present invention has a plurality of magnetic sensors disposed around a CRT display surface at angles that spread outward, and an output of the magnetic sensors having directivity. The direction and magnitude of the external magnetic field are detected based on the signal, and a correction current is generated based on the results.

[Function] If the detected external magnetic field change is not artificial, a correction current is generated based on the detected result to cancel the external magnetic field. Ignore the change and do not make any corrections.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.
Magnetic sensors 51-54 are attached to the four corners of the display screen as shown in FIG. 6, and their output signals are sent to amplifiers (AMP) 101-104 and ^/D converter 11□, respectively.
.about.114 to the comparison/judgment circuit 12.

In boat fishing, the external magnetic field is considered to be a DC magnetic field of approximately several Gauss, and since the output generated by the magnetic sensor due to this magnetic field is extremely small, the voltage is amplified approximately 1000 times by the amplifier 10.

This amplification provides an output of about 20 to 30 .mu.V.

The input signal range of the A/D converter 11 is 100V.
It is set to about. Further, polarity data corresponding to the polarity of the output signal of the AMPlo, that is, the polarity of the detection signal of the magnetic sensor is added to the output data of the A/D converter 11.

The signals supplied to the comparison/judgment circuit 12E are sent to the magnetic sensors 1~
4. Compare and judge the detection time and level. It consists of a firmware-controlled microprocessor and peripheral circuits. This comparison/judgment circuit 12 ignores the detection signal generated from only one magnetic sensor as being due to an artificial cause, and compares the level of only the detection signals detected from four magnetic sensors at approximately the same time, By adding polarity data, it is divided into a component perpendicular to the CRT display surface (BCZ in FIG. 6) and a component parallel to the CRT display surface (Bc-y in FIG. 6). The comparison/judgment circuit generates rotational distortion correction data for the component Bcz, and generates vertical/lateral movement correction data for the component (Bc yaw).

By comparing the detection outputs of four magnetic sensors, C
The component perpendicular to the RT display surface (Bcz) and the component parallel to the RT display surface (Be
-y) is achieved by the directivity of the magnetic sensor and by attaching it around the CRT display surface at an angle that extends outward.

If the magnetic sensors are installed in this manner, each of the magnetic sensors (5□ to 54 in FIG. 1) will send out almost the same output for a magnetic field that enters perpendicularly to the CRT surface in FIGS. 1 and 6. In this case, the comparison/judgment circuit 12 shown in FIG. 1 outputs Bcz correction (rotational distortion correction) data.

For a magnetic field that enters the CRT display surface at a certain angle,
The output of each magnetic sensor is not the same depending on the directivity and mounting angle of the magnetic sensor, and a sensor whose directivity matches the direction of the external magnetic field will send out a large output. In this way, the comparison/judgment circuit 12 performs B. In addition to 2 corrections,
(BC, -,) correction (vertical and horizontal movement correction) data is also output.

The rotational distortion correction data is converted into an analog signal by the D/A converter 13 shown in FIG.
5, the current (about several amperes) necessary to generate a sufficient correction magnetic field is supplied. The vertical/lateral movement correction data is converted into analog signals (X, Y correction signals) by D/A converters 161 and 162, amplified by the deflection amplifier 17, and supplied to the main deflection coil 18.

The timing of these operations is shown in FIG. 2, and the firmware control flow of the comparison/judgment circuit 12 is shown in FIG.
FIGS. 2(a) to 2(d) show the magnetic sensor 5! 54, and the sensor output with symbol "A" is the output of only a certain sensor, so it is ignored as an artificial signal and no correction is made. However, if a magnetic field is not applied perpendicularly to the CRT display surface in the area indicated by range A, output signals will be generated from all four magnetic sensors, so the second section (e)
A rotational distortion correction current is generated as shown in .

As a result, an operation is performed to cancel the external magnetic field, the magnetic field acting on the magnetic sensor is reduced, and the signals detected by each magnetic sensor are reduced, as shown by the dashed lines in Figure 2 (a) to (d). do.

On the other hand, when an external magnetic field enters the CRT display surface from below in range B, the amount detected by each sensor differs depending on its position, as shown in FIGS. 2(a) to 2(d). Depending on the level of this detection signal, a rotational distortion correction current as shown in FIG. 2(e) and an X correction signal as shown in FIG. 2(g) are generated. The magnetic field is corrected by this signal, and the current detected by the magnetic sensor gradually decreases as shown by the dashed line in FIGS. 2(a) to 2(d). Range C shows an example where the absolute value of the external magnetic field is equal to range B, but the direction is opposite.

These controls are performed according to the procedure of the flowchart shown in FIG. First, the detection operation starts in step 100, and in step 101, the magnetic sensor (MSG)
Detection data 1 to 4 are captured, and step 1
In step 02, comparison of detected data is performed. As a result, if it is determined in step 103 that the detection signals of magnetic sensors 1 to 4 are temporally aligned, each detection signal is compared in step 1.04, and polarity data is added to determine the direction of the external magnetic field. .

This determination is performed, for example, as follows.

(a) When the output absolute values of the magnetic sensors 51 to 54 are substantially equal...the external magnetic field is determined to be perpendicular to the CRT display surface, and rotational distortion correction data is output.

(b) When the absolute value of the output of the magnetic sensor 52.54 is larger than the absolute value of the output of the magnetic sensor 51.53...The external magnetic field is determined to be in the downward direction of the CRT, and the rotational distortion correction data and
Output directional movement correction data.

(e) When the absolute output value of the magnetic sensor 53.54 is larger than the absolute output value of the magnetic sensor 51.52...The external magnetic field is determined to be in the right direction of the CRT, and the rotational distortion correction data and Y
Output directional movement correction data.

(d) The absolute value of the output of the magnetic sensor 54 is the magnetic sensor 51.
When it is larger than any of the output absolute values of 52.5s...
...The external magnetic field is determined to be in the lower right direction of the CRT, and rotation correction data and X and Y direction movement correction data are output.

(e) (a) to (d) depending on the detection signal polarity of the magnetic sensor
The polarities of rotational distortion correction data, X-direction movement correction data, and Y-direction movement correction data are determined.

Through the above processing, correction data is output in step 105, and the operations of step 105 and step 106 are repeated to search for the level of correction data that minimizes the absolute value of the detection data of each magnetic sensor.
In step 07, the correction data that minimizes the absolute value of the detection data of each magnetic sensor is held for a certain period of time. If there is a change in the detection data of each magnetic sensor in step 108, the process returns to step 100. If there is no change, the process returns to step 107 and the correction data at the same level is held again for a certain period of time.

In addition, if it is determined in step 103 that the detection signals of the magnetic sensors 51 to 54 are not aligned in time, this is a case where one sensor outputs a detection output independently as shown in step 109, and this is due to human causes. It is ignored and the process returns to step 100.

By performing such processing, external magnetic fields from any direction can be canceled out.

Note that when a correction current is applied to the correction coil, a magnetic field from the correction coil enters the magnetic sensor, but when a correction current is applied, a magnetic field is normally generated in a direction that cancels out the external magnetic field, so the detection output becomes small. Correction data is output until this detected output does not become smaller than a certain limit. When the detected data becomes minimum, the external magnetic field and the correction magnetic field are in equilibrium, so the correction data is held. After a certain period of time, if the external magnetic field changes and this equilibrium state is disrupted, the detection operation is repeated again.

[Effects of the Invention] As explained above, the present invention arranges a magnetic sensor around the CRT display surface, detects the level difference when the output signals are generated at the same time, adds polarity data, and generates a correction current. Since it is designed to generate a
In addition, since it is possible not to react to artificial changes in the magnetic field, there is an effect that even if there is an external magnetic field and the field fluctuates, the display can always be displayed in a state where the influence of the external magnetic field is greatly reduced.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram of each part, Fig. 3 is a flowchart of a control operation to cancel the magnetic field, and Figs. 4 to 6 explain the influence of an external magnetic field. This is a diagram for 1... Shield case, 51-54... Magnetic sensor, 12... Comparison/judgment circuit, 15... Correction coil.

Claims (1)

[Claims] A CRT external magnetic field correction device that supplies a correction current to a correction coil to cancel the external magnetic field when an external magnetic field acts on the CRT, comprising: a plurality of magnetic sensors disposed around a CRT display surface; , External magnetic field specification detection means for detecting the magnitude and direction of the magnetic field acting based on the amount of change, polarity, and state of change when the outputs of the magnetic sensors change simultaneously; and a correction device that generates a correction current based on the detection results. 1. An external magnetic field correction device for a CRT, comprising current generating means.