JPH07220201A - Video tape testing equipment - Google Patents

Abstract

(57) [Summary] [Constitution] The mixer 14 time-division-multiplexes the RF signals reproduced by the A channel head 12a and the B channel head 12b to generate a mixed RF signal. The envelope detection circuit 20 has a time constant shorter than the head switching cycle and performs envelope detection of the MIXRF signal to generate an RF envelope signal. Based on the RF envelope signal and the SWP signal from the rotary servo circuit 15, the level measuring device detects a level fluctuation for a long time and a clog that is a level drop for a short time for each head of each channel. [Effect] The clog and level fluctuation can be detected by using one envelope detection circuit, and the cost can be reduced as compared with the conventional device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video tape test apparatus, and more particularly to a video tape test apparatus for detecting level fluctuations of a video tape, so-called clogs.

[0002]

2. Description of the Related Art Conventionally, in a test device for testing a video tape, a reference signal is recorded in advance over the entire length of the video tape and the video tape is reproduced. Then, the envelope signal of the signal (RF signal) reproduced by the rotary head at the time of reproduction is detected, and the envelope signal of this RF signal (hereinafter referred to as RF envelope signal).
The video tape test is conducted by measuring the level drop of about several milliseconds and the level fluctuation for a long time such as 2 hours. Furthermore, in the endurance test, rewinding and reproduction are repeated to measure the level fluctuation.

By the way, in a video tape test apparatus using a rotary head having heads of two channels A and B, for example, the RF signal reproduced by the head of channel A is of the channel B as shown in FIG. 9A. When the head is reproducing (hereinafter referred to as B channel period)
Has a level of 0. Therefore, in order to detect the level fluctuation, it is necessary to make the time constant of the envelope detection circuit that detects the RF envelope signal sufficiently longer than the B channel period, as shown in FIG. 9B. However, with the envelope detection circuit having this time constant, as shown in FIGS. 10A and 10B, it is not possible to detect a level drop (so-called clog) for a short time period shorter than the A channel period. On the other hand, an envelope detection circuit having a short time constant that can detect clogs cannot detect level fluctuations as described above.

[0004]

That is, in the conventional device, the envelope detection circuit for clog detection and the envelope detection circuit for level fluctuation detection are required. Therefore, in FIG.
1A and 1B, a signal obtained by time division multiplexing the RF signal signal of the A channel and the RF signal of the B channel (hereinafter,
It is called a MIXRF signal. ), It is conceivable to detect the clog and the level fluctuation by using an envelope detection circuit having a time constant at which the clog can be detected.
As shown in FIG. 12, when the level of the RF signal is different for each channel, the level of the RF envelope signal is different for each channel as shown in FIG. 12B, and the above-mentioned level fluctuation cannot be detected.

Further, when the clog occurs as shown in FIG. 13A over, for example, two A channel periods, there is a possibility that it is detected that the clog occurs twice as shown in FIG. 13B. is there.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a video tape test apparatus capable of detecting clogs and level fluctuations by using one envelope detection circuit.

[0007]

In order to solve the above-mentioned problems, a first video tape testing apparatus according to the present invention comprises a rotary head equipped with heads of a plurality of channels and a reference signal recorded on the video tape. The signal of each channel obtained by reproducing by the rotary head is envelope-detected for envelope-detecting the reproduction signal time-division-multiplexed, the envelope signal from the envelope-detector, and the switching of the heads of a plurality of channels. Level measuring means for measuring the level of the reproduction signal for the head of each channel based on the head switching signal shown.

Further, the second video tape testing apparatus according to the present invention is the same as the first video tape testing apparatus, wherein the time constant of the envelope detecting means is set to a value smaller than the cycle of the head switching signal and the level is measured. The means is characterized by measuring a short time level drop of the reproduced signal to the head of each channel and a long time level fluctuation.

[0009]

In the video tape testing apparatus according to the present invention, the signals of the respective channels obtained by reproducing the video tape by the rotary head are subjected to envelope detection of the reproduction signal obtained by time division multiplexing, and the obtained envelope signal and a plurality of channels. The level of the reproduction signal for the head of each channel of the video tape is measured based on the head switching signal indicating the head switching.

Further, in the video tape testing apparatus according to the present invention, the time constant of the envelope detecting means is set to a value smaller than the cycle of the head switching signal, and the reproduced signal is subjected to the envelope detection to obtain the obtained envelope signal. Based on the head switching signal, a level drop shorter than the head switching period, for example, a clog is detected. In addition, the level fluctuation for a long time is measured.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a video tape testing apparatus according to the present invention will be described below with reference to the drawings. A video tape test apparatus to which the present invention is applied is, for example, as shown in FIG. 1, a rotary head 10 equipped with heads of a plurality of channels.
And an envelope detection circuit 20 for performing envelope detection of a reproduction signal obtained by time-division-multiplexing the signals of the respective channels obtained by reproducing the video tape 1 by the rotary head 10, and the envelope from the envelope detection circuit 20. A level measuring device 30 for measuring the level of a reproduction signal for each head of the video tape 1 based on a signal and a head switching signal for switching the heads of the plurality of channels.

As shown in FIG. 1, the rotary head 10 includes a plurality of, for example, two A channel heads 12a and B channel heads 12b mounted facing the rotary drum 11, and the A channel heads. 12a, B
Amplifiers 13a and 13b for amplifying the RF signal from the channel head 12b, and the amplifiers 13a and 13b, respectively.
The mixer 14 for adding the RF signals amplified in 1. and the rotary servo circuit 15 for servo-controlling the rotary drum 11 are provided.

The amplifiers 13a and 13b amplify the RF signals reproduced by the A channel head 12a and the B channel head 12b, respectively. The mixer 14 adds the amplified RF signals of the respective channels, and as shown in FIG. 2A, for example, the A channel RF signal and the B channel RF signal are time-division multiplexed, that is, assigned to each head. RF of each channel in a time slot
A mixed RF signal (hereinafter referred to as MIXRF signal) in which the signal is inserted is generated, and this MIXRF signal is supplied to the envelope detection circuit 20.

On the other hand, the rotary servo circuit 15 performs servo control so that the rotational speed of the rotary drum 11 is constant, and a head switching signal (hereinafter referred to as SWP signal) for switching between the A channel head 12a and the B channel head 12b. ) Is supplied to the level measuring device 30. This SW
The P signal is synchronized with the rotation of the rotating drum 11, and is, for example, as shown in FIG.
As shown in C, both edges coincide with the channel switching of the MIXRF signal. By the way, this rotary head 1
Instead of 0, a normal video tape recorder (hereinafter V
It is called TR. )) With the MIXR from this VTR
The F signal may be supplied to the envelope detection circuit 20.

The envelope detection circuit 20, as shown in FIG. 3, for example, includes an amplifier 21 for amplifying the MIXRF signal from the mixer 14, and a detector 22 for envelope detection of the MIXRF signal from the amplifier 21. An amplifier 23 for adjusting the offset of the envelope signal from the detector 22.

As shown in FIG. 3, the detector 22 is composed of a transistor 22a, a capacitor 22b for determining a time constant at the time of envelope detection, and a resistor 22c. Then, the detector 22 envelope-detects the MIXRF signal amplified by the amplifier 21 to generate an envelope signal (hereinafter, referred to as an RF envelope signal), as shown in FIG. 2B, and the RF envelope signal is generated. Amplifier 2
Supply to 3. The amplifier 23 has a resistor 2 connected to the power supply.
4, the offset voltage can be adjusted, the RF envelope signal is amplified, an offset is given, and the amplified RF envelope signal is supplied to the level measuring device 30. By the way, the capacitor 22b
The time constant of the detector 22, which is determined by the product of the capacitance value of the resistor 22c and the resistance value of the resistor 22c, is greater than the period of the SWP signal, that is, A
The value is smaller than the channel period. That is, for example, as shown in FIG. 4A, the time constant is a value at which a clog, which is a level drop for a short time, can be detected based on the RF envelope signal, for example, about 1 msec. In addition,
FIG. 4B shows an RF envelope signal when envelope detection is performed on the MIX RF signal with a conventional time constant for detecting a long-term level fluctuation.

Specifically, as shown in FIG. 5A, for example,
When the MIXRF signal composed of the RF signal of the A channel and the normal RF signal of the B channel, which are lowered in level when switching the channels, is supplied, the envelope detection circuit 2
For 0, the MIXRF signal is subjected to envelope detection with a time constant of about 1 msec, and as shown in FIG. 5B, an RF envelope signal whose level decreases at the beginning and end of the A channel is output.

As shown in FIG. 1, the level measuring device 30 is an analog / digital converter (hereinafter referred to as an A / D converter) which converts the RF envelope signal from the envelope detection circuit 20 into data. 31 and a parallel I / O for taking in the SWP signal from the rotary servo circuit 15
32, a program memory 33 in which a measurement program is stored, a data memory 34 in which an RF envelope signal converted into data from the A / D converter 31 is stored, and a CPU 35 which executes the measurement program. Prepare

Then, the A / D converter 31 samples the RF envelope signal at a predetermined sampling period and converts it into data. In addition, the parallel I / O 32
The SWP signal supplied from the rotation servo circuit 15 is fetched as data for identifying the A channel and the B channel. Here, each data from the A / D converter 31 is called a sample value, and the data from the parallel I / O 32 is S.
It is called the WP value. These sample values and SWP values are CP
It is temporarily stored in the data memory 34 under the control of U35.

The program memory 33 pre-stores a measurement program including a level fluctuation measurement program, a clog detection program, and the like.
Executes a measurement program to measure a level change for a long time and detect a clog which is a level decrease for a short time.

Specifically, in the measurement of level fluctuation, CP
U35 operates according to the flowchart shown in FIG. 6, for example. That is, in step ST1, CPU3
5 is 1 of the sample value and the SWP value from the data memory 34
The set is read out, and the process proceeds to step ST2.

In step ST2, the CPU 35
The SWP value is determined. When the SWP value indicates the A channel, the process proceeds to step ST3, and when the SWP value indicates the B channel, the process proceeds to step ST5.

In step ST3, the CPU 35
The sample value is added to the cumulative value of the A channel to obtain a new cumulative value of the A channel, and the process proceeds to step ST4.

At step ST4, the CPU 35
One is added to the sample number of the A channel to obtain a new sample number of the A channel, and the process proceeds to step ST7.

On the other hand, in step ST5, the CPU 3
5 adds the sample value to the cumulative value of B channel,
The cumulative value of the new B channel is calculated, and the process proceeds to step ST6.

At step ST6, the CPU 35
One is added to the number of B channel samples to obtain a new number of B channel samples, and the process proceeds to step ST7.

In step ST7, the CPU 35
It is determined whether or not the unit time has elapsed, and if so, the process proceeds to step ST8. If not, the process for one set of data read at step ST1 is terminated, and the process for the next set of data is completed. To start. That is, it returns to step ST1.

At step ST8, the CPU 35
By dividing the cumulative value of A channel by the number of samples,
Obtain the average value of channel A. Also, the average value of the B channel is obtained by dividing the cumulative value of the B channel by the number of samples. Then, after storing these average values in the data memory 34, the process proceeds to step ST9.

In step ST9, the CPU 35
All accumulated values and the number of samples are initialized to 0, and the process returns to step ST1.

Thus, the average value of the level of each channel can be obtained every unit time. In other words, by using the envelope detection circuit 20 having a short time constant capable of detecting clogs, R for the head of each channel is used.
It is possible to measure long-term level fluctuations of the F signal.

Next, the detection of the clog will be described. In detecting this clog, the CPU 35 operates according to the flowchart shown in FIG. 7, for example. That is,
In step ST1, the CPU 35 reads one set of sample value and SWP value from the data memory 34, and proceeds to step ST2.

At step ST2, the CPU 35
The SWP value is determined. When the SWP value indicates the A channel, the process proceeds to step ST3, and when the SWP value indicates the B channel, the process proceeds to step ST12.

In step ST3, the CPU 35
It is determined whether or not the sampled value is equal to or larger than a predetermined threshold value TH, and if it corresponds, the process proceeds to step ST4, and if not, the process proceeds to step ST7.

At step ST4, the CPU 35
It is determined whether the timer of channel A for measuring the duration of the clog is 0, and if it is, step ST10.
If not, go to step ST5.

At step ST5, the CPU 35
After the value of the timer of channel A is stored in the data memory 34 as the duration of the clog, the process proceeds to step ST6.

At step ST6, the CPU 35
Initialize the timer of A channel to 0, and step ST1
Go to 0.

On the other hand, in step ST7, the CPU 3
5 determines whether the timer of the A channel is 0, and if so, proceeds to step ST8, and otherwise proceeds to step ST9.

In step ST8, the CPU 35
The timer for channel A is set to 1, and the process proceeds to step ST10.

In step ST9, the CPU 35
One is added to the timer for channel A to make a new timer for channel A, and the process proceeds to step ST10.

In step ST10, the CPU 35
Determines whether the timer of the B channel is 0, and when it is true, ends the process for one set of data read in step ST1 and starts the process for the next set of data. That is, it returns to step ST1. On the other hand, if not applicable, the process proceeds to step ST11.

In step ST11, the CPU 35
Adds 1 to the B channel timer to make a new B channel timer, and returns to step ST1.

On the other hand, in step ST12, the CPU
35 determines whether the sample value is equal to or greater than a predetermined threshold value TH,
When it corresponds, it progresses to step ST13, and when it does not correspond, it progresses to step ST16.

At step ST13, the CPU 35
Determines whether the timer of the B channel for measuring the duration of the clog is 0, and if it is, the step ST
If not applicable, go to step ST14.

In step ST14, the CPU 35
Stores in the data memory 34 the value of the timer for channel B as the duration of the clog, and then proceeds to step ST1.
Go to 5.

In step ST15, the CPU 35
Initializes the timer for channel B to 0, and
Proceed to T19.

On the other hand, in step ST16, the CPU
35 determines whether the timer for channel B is 0, and if so, proceeds to step ST17, and otherwise proceeds to step ST18.

In step ST17, the CPU 35
Sets the timer of channel B to 1, and step ST19
Proceed to.

In step ST18, the CPU 35
Adds 1 to the timer for channel B to make a new timer for channel B, and proceeds to step ST19.

In step ST19, the CPU 35
Judges whether the timer of the A channel is 0, and if so, proceeds to step ST20, and if not, returns to step ST1.

In step ST20, the CPU 35
Adds 1 to the timer for channel A to make a new timer for channel A, and returns to step ST1.

Here, for example, as shown in FIG. 8A, M in which a clog has occurred over two A channel periods.
A specific operation when the IXRF signal is obtained will be described. For example, assuming that the threshold value TH is 50% of the maximum value of the RF envelope signal, as shown in FIG. 8B, in the A channel period before time t ₁ , the sample value of the A channel is larger than the threshold value TH, so the CPU 35 ,
The operations of steps ST1, ST2, ST3, ST4 and ST10 are repeatedly executed in order.

Then, since the sample value becomes less than the threshold value TH at the time t ₁ , the CPU 35 causes the step S
Each operation of T1, ST2, ST3, ST7, ST8, ST10 is executed in order, and the timer of A channel is set to 1,
Return to step ST1. In the subsequent A channel period until time t ₂ , the CPU 35 has steps ST1 and ST
By repeating the operations of 2, ST3, ST7, ST9, and ST10, the timer for channel A is set to 1
Increase by one.

In the B channel period from time t ₂ to time t _3, since the sample value of the B channel is larger than the threshold value TH, the CPU 35 causes the steps ST1, ST
By repeating the operations of 2, ST12, ST13, ST19, and ST20, the timer of the A channel is incremented by one.

From time t ₃ to time t _{4 in the} A channel period.
Up to the point, the sample value of the A channel is smaller than the threshold value TH, so the CPU 35 executes steps ST1, ST2,
By repeating the operations of ST3, ST7, ST9, and ST10, the timer of the A channel is incremented by one.

Then, since the sample value becomes equal to or larger than the threshold value TH at the time t ₄ , the CPU 35 causes the step S
T1, ST2, ST3, ST4, ST5, ST6, ST
Each operation of 10 is sequentially executed, and the value of the timer of the A channel, that is, the time T is stored in the data memory 34 as the Clog duration time of the A channel.

Thus, a clog generated over two A channel periods can be detected as one clog.

[0057]

As is apparent from the above description, according to the present invention, the signal obtained from each channel obtained by reproducing the video tape by the rotary head is subjected to the envelope detection of the reproduced signal which is time-division multiplexed to obtain the envelope. By measuring the level of the reproduction signal based on the line signal and the head switching signal indicating the switching of the heads of a plurality of channels, it is possible to measure the level fluctuation for a long time with respect to the head of each channel of the video tape, and It is possible to detect a clog, which is a drop in the level of time.

Further, according to the present invention, the time constant of the envelope detecting means is set to a value smaller than the cycle of the head switching signal, the reproduced signal is subjected to the envelope detection, and the envelope signal and the head switching signal obtained are used. By measuring the level of the reproduced signal, it is possible to detect a clog, which is a level drop that is shorter than the head switching cycle, for each head of each channel, and it is also possible to detect long-term level fluctuations and envelopes with a short time constant. It can be detected using a line detection circuit. In other words,
The clog and level fluctuation can be detected by using one envelope detection circuit, and the cost can be reduced as compared with the conventional device.

[Brief description of drawings]

FIG. 1 is a block diagram showing a specific configuration of a video tape test apparatus to which the present invention has been applied.

FIG. 2 is a diagram showing a waveform of an RF envelope signal when envelope detection is performed on a normal MIX RF signal.

FIG. 3 is a diagram showing a specific circuit configuration of an envelope detection circuit which constitutes the video tape testing device.

FIG. 4 is a diagram showing a specific waveform of a MIXRF signal for explaining a time constant of the envelope detection circuit.

FIG. 5 is a diagram showing a waveform of an RF envelope signal when envelope detection is performed on a MIX RF signal having a clog.

FIG. 6 is a flowchart for explaining an operation of measuring level fluctuations in the video tape testing device.

FIG. 7 is a flowchart for explaining the operation of clog detection in the video tape testing device.

FIG. 8: M generated by clogs straddling channels
It is a figure which shows the waveform of the RF envelope signal at the time of carrying out the envelope detection of the IXRF signal.

FIG. 9 is a diagram showing a waveform of an RF envelope signal when a 1-channel RF signal is detected by an envelope detection circuit having a long time constant.

FIG. 10: RF of one channel with clogs
R when a signal is detected by an envelope detection circuit with a long time constant
It is a figure which shows the waveform of an F envelope signal.

FIG. 11 is a diagram showing a waveform of an RF envelope signal when a 2-channel RF signal is detected by an envelope detection circuit having a short time constant.

FIG. 12 is a diagram showing a waveform of an RF envelope signal when envelope detection is performed on MIXRF signals having different levels between channels.

FIG. 13 is a diagram showing a waveform of an RF envelope signal when envelope detection is performed on a MIX RF signal generated by a clog spanning channels.

[Explanation of symbols]

 1 Magnetic Tape 11 Rotating Heads 12a, 12b Head 14 Mixer 15 Rotating Servo Circuit 20 Envelope Detection Circuit 30 Level Measuring Device

Claims (2)

[Claims] 1. A rotary head equipped with a multi-channel head, and a reproduction signal obtained by time-division-multiplexing a signal of each channel obtained by reproducing a reference signal recorded on a video tape by the rotary head. Level measuring means for measuring the level of the reproduction signal for the head of each channel based on the envelope detecting means, the envelope signal from the envelope detecting means, and the head switching signal indicating the switching of the heads of the plurality of channels. And a video tape testing device. 2. The time constant of the envelope detecting means is set to a value smaller than the cycle of the head switching signal, and the level measuring means reduces the level of the reproduced signal to the head of each channel for a short time and for a long time. 2. The video tape test apparatus according to claim 1, wherein the level fluctuation of the video tape is measured.