JPH0366876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic demagnetizing device for a video monitor, and in particular, to an automatic demagnetizing device for a video monitor, in particular, an automatic demagnetizing device for automatically demagnetizing a shadow mask due to the influence of earth's magnetism and external magnetism when the monitor is moved. The present invention relates to a magnetic change detection circuit that detects signals.

In conventional magnetic degaussing devices, the monitor was manually demagnetized when the power was turned on, but observers often did not notice convergence errors caused by moving the monitor, making it difficult to achieve good convergence. I couldn't get it.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic video monitor demagnetization device that automatically demagnetizes a shadow mask by eliminating the situation where good convergence cannot be obtained due to convergence errors caused by movement of the video monitor.

In other words, it has a configuration in which a magnetic field detector detects the magnetic state of the monitor, stores it in memory, detects a magnetic abnormality using a comparison circuit, and automatically demagnetizes the monitor by passing current through a degaussing coil. be.

Here, "demagnetization" as used herein means taking into account the direction of the external magnetic field and aligning the magnetic moment on the shadow mask in a certain direction, that is, in a direction that cancels out the external magnetic field.

Hereinafter, the present invention will be explained in detail based on the drawings.

1 is a magnetic field detector, as shown in FIG.
It is provided in a portion of the monitor 2 that is not affected by the magnetic field (the rear corner of the monitor 2). A magnetic field detector outputs an output that depends on the magnetic flux density and magnetic flux direction. For example, the output voltage V _H of a Hall element is determined by B representing the magnetic flux density and θ representing the angle between the surface of the element and the direction of the magnetic flux.
Then, it can be expressed as V _H = KB _cps θ+α. The output of this magnetic field detector 1 is input to an amplifier 3, and as shown in FIG. , R4 are provided. A limit value generating means is configured to output a reference signal A, an upper limit signal B, and a lower limit signal C from each resistance contact of the dividing resistors R2, R3, and R4. Among these signals A, B, and C, the reference signal A is the 1st A/D
to the converter 4, the upper limit signal B to the second A/D converter 5,
The lower limit signals C are each input to the third A/D converter 6. The output signal of the first A/D converter 4 is configured to be input to the first comparator 7 and the second comparator 8 as a reference signal EA for comparison with the previous magnetic field. A power supply circuit 9 generates an initial pulse when the power is turned on. This initial pulse is input to the sample clock generation circuit 10, which is a memory control circuit consisting of an OR circuit (logical sum), and becomes the output signal of the sample clock generator 10 as it is to operate the two memories 11 and 12. The output signal (upper limit value) of the second A/D converter 5 is sent to the first memory 11 as the magnetic field information of the current position.
The output signal (lower limit value) of the third A/D converter 6 is
The data is input to the storage device 12. The upper limit value Eu of the first memory 11 is input to the first comparator 7, and the lower limit value EL of the second memory 12 is input to the second comparator 8, and a comparison is made with the subsequent magnetic field. In 7
When E _A > Eu, the output signal of the first comparator 7 Ecu = 1
(when it exceeds the previous upper limit of the magnetic field).
In the second comparator 8, when E _A <E _L , the output signal Ec _L of the second comparator 8 becomes 1 (when the magnetic field falls below the lower limit of the previous magnetic field). The outputs of the Ecu signal of the first comparator 7 and the Ec _L signal of the second comparator 8 are input to the trigger circuit 13, and when the logical sum of Ecu and Ec _L becomes "1", a trigger pulse 13a is generated. Occur. The pulse generator 14 generates a pulse for a certain period of time in response to the trigger pulse 13a generated by the trigger circuit 13, and generates a pulse for a certain period of time.
is input to the drive circuit 15. The signal input to this sample clock generator 10 is generated when different from the previous magnetic field, but is treated in the same way as the output signal of the power supply circuit 9. The drive circuit 15 is inputted to the drive circuit 15 by an output signal from the pulse generator 14, and is turned on when a pulse is generated for a certain period of time from the pulse generator 14 to erase the erase coil 1.
As shown in FIG. 2, a damped vibration current is applied to the monitor 6 near the shadow mask of the monitor 2 to demagnetize the magnetism.

If the direction of the external magnetic field has not changed since the time of demagnetization, the direction of the magnetic moment will remain constant and demagnetization is not necessary. However, once the direction of the external magnetic field changes due to changing the orientation of the device, etc. The magnitude of the magnetic moment when viewed from the direction of the shield (or the internal shield member) has changed, and the shadow mask will now have a magnetic moment with a magnitude different from the previously magnetized magnetic moment.

In such a state, the electron beam is bent, causing color shift and color unevenness. In this case, it becomes necessary to perform demagnetization again in a new magnetic environment. Furthermore, even if the magnetic flux decreases relatively, the magnetic moment on the shadow mask (or internal shield member) is magnetized by the previous magnetic bias, and unnecessary magnetism is generated in the shadow mask (or internal shield member), so demagnetization is not possible. It becomes necessary to do this.

As described above, the automatic magnetic degaussing device for a video monitor according to the present invention includes a magnetic detector, an intensifier that divides the detection output into multiple levels, and two memory devices that store the upper and lower limits of these multiple levels. Since it is equipped with a comparison circuit that compares this level with a reference value, even if it is affected by an unnecessary magnetic field, it can automatically demagnetize the shadow mask and display a stable color image on the cathode ray tube.

[Brief explanation of drawings]

The drawings are for showing an automatic demagnetizing device for a video monitor according to the present invention, and FIG. 1 is an overall block diagram, FIG. 2 is a plan view showing the monitor device, and FIG. 3 is a plan view showing the monitor device.
The figure is a circuit diagram of the main part. DESCRIPTION OF SYMBOLS 1... Magnetic field detector, 2... Plan view of monitor device, 3... Amplifier, 4... First A/D converter, 5
...2nd A/D converter, 6...3rd A/D converter,
7...First comparator, 8...Second comparator, 9...Power supply circuit, 10...Sample clock generator, 11
...First memory device, 12...Second memory device, 13...
Trigger circuit, 14... Pulse generator, 15... Drive circuit, 16... Demagnetizing coil.

Claims (1)

[Scope of Claims] 1. A magnetic detector, an amplifier that inputs, amplifies and outputs the signal of the magnetic detector, and upper and lower limits corresponding to a predetermined width for the amplified output from the amplifier. limit value generation means for outputting a signal; storage means for storing upper and lower limit signals having a predetermined width from the limit value generation means in response to input of a control signal; and storage means for updating the memory each time in response to input of a control signal; and a comparison means for comparing the output of the amplifier with the stored value from the storage means and outputting a signal when the output of the amplifier exceeds the predetermined width; It consists of a storage control circuit consisting of a sample clock generator that outputs a control signal to the storage means, and a degaussing means that inputs the output from the comparison means and drives the degaussing coil. An automatic image monitor demagnetizing device characterized by driving an image monitor. 2. The image monitor automatic demagnetizing device according to claim 1, wherein the limit value generation means having a predetermined width outputs a value obtained by adding a predetermined amount to the output value of the amplifier and a value obtained by subtracting the predetermined amount.