JPS6128253Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an output voltage measuring device for a rotating magnetic head.

A rotating magnetic head performs magnetic recording and reproduction while scanning a magnetic tape wound around a guide cylinder.
Subtle variations in the shape and protrusion of the tape contacting surface have a large effect on the recording and reproducing characteristics. Therefore, a pair of rotating magnetic heads are attached to a video tape recorder for testing while being fixed to a rotating disk, and a recording/reproducing characteristic test is performed. The traditional test method is
It reproduces and scans the recording track that it has formed, synchronizes the reproduction output with the vertical synchronization period, and displays it on an oscilloscope. The quality of both rotating magnetic heads is inspected by visually measuring the level and using a conversion table to determine whether it is within a predetermined ratio. However, such a method is inevitably disadvantageous in that it not only requires manpower and time, but also has low inspection accuracy.

Therefore, in view of the above-mentioned points, the present invention proposes an output level measuring device that automatically and highly accurately measures the reproduction output level in the vertical synchronization signal insertion area at the start of scanning, where the reproduction output level tends to be low. It is.

The present invention will be described below with reference to an illustrative embodiment. In this embodiment, a rotary disk on which a pair of magnetic heads having different azimuths are mounted and fixed is temporarily attached to a guide cylinder of a video tape recorder for testing, and the recording and reproducing characteristics of the magnetic heads are tested. , the main components are a recording circuit A, an inspection videotape recorder B, a playback circuit C, and an arithmetic circuit D.
Consists of.

Figure 1 shows a circuit block diagram of the device of this embodiment. In the figure, number 1 is an oscillation circuit that derives a 5MHz oscillation output for a fixed period in recording mode, and number 2 is an oscillation circuit that divides a 5MHz signal by 1/5. /5 frequency divider circuit, 3 is 1MHz signal
4 is a recording amplifier circuit that amplifies the output of the 5MHz signal; 5 is a head input switch that supplies the circuit output to the first rotating magnetic head _H1 in the first half and the second rotating magnetic head _H2 in the second half. circuit,
6 and 7 are the first and second rotating magnetic heads during recording.
Recording circuit outputs are supplied to H ₁ and H ₂ , and first and second reproduction outputs P ₁ and P ₂ of the rotating magnetic head are supplied to the reproduction circuit C during reproduction. A first/second recording/playback switching circuit, 8 a mode setting circuit for controlling the mode of the inspection video tape recorder by one output of the control circuit 10, and 9 a complementary head switching circuit in relation to the rotation of the rotary disk. Rotation detection circuit for deriving output, 1
1 is a reproduction output detection circuit that detects the first reproduction output _P1 , and 12 is the input first or second reproduction output.
A regenerative amplifier circuit that amplifies P ₁ and P ₂ ; 13 an envelope detection circuit that performs envelope detection of the circuit output; and 14 a scanning starting point each time the frequency of the first and second regenerative outputs P ₁ and P ₂ changes. 10 consecutive envelopes of 14 points are sampled at regular intervals in relation to the rise of the head switching output, and the sampled values are
An AD conversion circuit 15 performs AD conversion to derive the output, and a sampling area determination circuit 16 selects a corresponding switching output based on the output of the regeneration detection circuit 11.
a sampling value storage circuit 18 for reading sampling values at each corresponding sampling point in order to average the sampling values according to the designation of the address designation circuit 17 every time the frequency of the second reproduction outputs P ₁ and P ₂ changes;
19 is an averaging circuit that averages the sampling values derived 10 at a time, and 19 is the addressing circuit 17 that stores a reference level corresponding to each sampling point.
20 is a comparison circuit that compares the average output and the reference level at each sampling point and outputs an output if it is below the reference level; 21 is a comparison circuit that derives the reference level based on the specification of the comparison output; Lamp R ₁ or R ₂ for rotating magnetic head
Each shows a defect detection circuit that turns on the light.

Therefore, according to this embodiment, first, the test video tape recorder is brought into a constant speed driving state in the recording mode in synchronization with a vertical synchronizing signal separated from a suitable video signal supply means, and the oscillation circuit 1 is activated by the control output.
was activated and the frequency was divided by 1/5 from the 5MHz recording signal.
The 1MHz recording signal is alternately selected and amplified for a fixed period (about 1 second). Based on the amplified output and the control output, two types of recording signals are supplied to the first and second rotating magnetic heads H ₁ and H ₂ for a fixed period (about 2 seconds each) and are recorded on the magnetic tape. Next, the test video tape recorder B is rewound by a predetermined amount based on the control output, enters the playback mode, and after entering a constant speed running state, the first rotating magnetic head _H1
When the reproduction output P ₁ is derived, the output P ₁ is detected and the head switching output corresponding to the output P ₁ is input to the AD conversion circuit 14, and the period corresponding to the vertical synchronization signal insertion portion immediately after the reproduction output switching is performed. As shown in FIG. 2, the level of the envelope corresponding to 1 is sampled at 14 points per envelope and AD conversion is repeated 10 times to complete the first sampling. The sampling value derived by the above sampling is
Sequentially, the sampling values stored in the sampling value storage circuit 16 of the arithmetic circuit D are read out and averaged at the corresponding sampling points of each envelope, and it is determined whether or not the values are above the reference level.If the values are below the level, the first
Turn on lamp _R1 . Thereafter, when the reproduction frequency of the first reproduction output _P1 is changed, the above-mentioned sampling and comparison are performed again to determine whether the first rotary magnetic head _H1 is good or bad. Furthermore, the two frequencies of the second reproduced output derived thereafter are also similarly sampled and compared to determine whether the second rotating magnetic head _H2 is good or bad.

Therefore, in this embodiment, the reliability of the test is high because it is tested whether the level of the vertical synchronization signal insertion part of the envelope formed by the two types of reproduction frequencies of 1 MHz and 5 MHz is higher than the predetermined level. Since the control circuit automatically performs the inspection without waste, the inspection time can be kept to about 10 seconds.

As described above, the present invention has great effects because it can automatically perform more accurate and faster inspections than conventional visual inspections.

[Brief description of the drawings]

Figure 1 is a block diagram of an implementation circuit of the present invention;
The figures show the main part waveform diagrams. Explanation of the main drawing numbers: A...recording circuit, C...playback circuit, D...arithmetic circuit.

Claims (1)

[Scope of utility model registration request] A recording circuit that supplies a constant frequency signal to a rotating magnetic head that rotates at a constant speed when setting a recording mode, and an envelope of the playback output at the start of a playback scan of the rotating magnetic head in synchronization with a head output switching signal when setting a playback mode. 1. An output level measuring device for a rotating magnetic head, comprising a reproducing circuit that samples a line, and an arithmetic circuit that compares the sampled value with a reference level and determines the recording/reproducing characteristics of the rotating magnetic head.