SU1116456A1 - Device for measuring parameters of combined magnetic head stack - Google Patents

Abstract

DEVICE FOR MEASURING PARAMETERS UNIT COMBINED MAGNITNB1H HEADS, comprising a tape drive, an oscilloscope, reproducing amplifier with a fixed gain amplifier, the control reproducing head, the test signal generator and electrical- keys, characterized in that, with a view to spreading device functionality incorporated therein erase head, recording channel switch, magnetic head selector, playback channel switch, third harmonic band filter reference frequency, frequency reference bandpass, erase and biasing generators, attenuator, channel selector, timer, correction unit, variable gain amplifier, and control unit, the P1I erase head connected to the erase generator through the first key, write-switch inputs. connected to generators. the test signals and the output through the second key are connected to the recording head of the combined unit, the first and second inputs of the magnetic head selector are connected respectively to the playback head of the combi unit and to the serially connected test head playback and correction unit, and the output is connected to the inputs of the playback amplifiers adjustable and fixed gain, the first and second inputs of the com.setter of the playback channel are connected to the output of the playback amplifier and with a fixed gain, respectively, through the third frequency harmonic of the reference frequency harmonic and sequentially (Litally connected attenuator and frequency reference filter, the nerve and the third inputs of the channel selector are connected respectively to the output of the playback amplifier with adjustable gain and the playback channel switch, and the outputs are connected to the oscilloscope inputs, the timer is connected to the first and second keys, the control unit is connected to the channel selector, the switch the playback device, a magnetic head selector, a timer, a recording channel com commutator, the first, second, and a third key through which the magnetic biasing generator is connected to the recording channel switch.

Description

The invention relates to instrumentation, in particular, to devices for measuring parameters of magnetic heads.

A device for testing magnetic heads is known, comprising an endless loop of magnetic tape, an amplifier, a dial gauge and a measuring unit housed in a cassette made with connecting contacts 1.

It is also known a device for measuring the characteristics of a magnetic recording-reproducing process, comprising a tape driving mechanism, a recording-reproducing path, a measuring amplifier, a switch, a recording unit, multipliers, and a spectrum analyzer 2.

These devices allow to determine such parameters of magnetic heads as reproduction emf, quality factor, inductance, amplitude-frequency characteristic of recording-reproduction.

However, the known devices do not allow measuring such important recording parameters of a combined magnetic head as nominal bias current, nominal recording current, losses due to the skew between the gaps of the recording and reproducing heads, the level of signal penetration from the recording head into the reproducing at the upper frequency working range.

Closest to the present invention is a device for measuring parameters of reproducing magnetic heads, comprising an oscilloscope, a reproduction amplifier with a fixed gain, a control reproduction head, test signal generators and electric switches 3. This device measures the effective width of the working gap of the magnetic head.

But this device also does not allow to measure the indicated recording parameters of the combined magnetic head.

The aim of the invention is to extend the functionality of the device and to improve the measurement accuracy. To achieve this goal, a device for measuring the parameters of the combined magnetic head unit containing a tape mechanism, an oscilloscope, an amplifier reproduced with a fixed gain factor, a test control head, test signal generators and electrical switches, an erase head, a recording channel switch, a magnetic head selector , switch of the playback channel, third frequency harmonic filter of the reference frequency, frequency reference bandpass filter, generation Erasing and biasing, attenuator, channel selector, timer, correction unit, playback amplifier with adjustable gain and control unit, the erase head connected to the erase generator through the first key, the inputs of the recording channel switch are connected to the test signal generators, and the output through the second the key is connected to the recording head of the combined unit, the first and second inputs of the magnetic head selector are connected respectively to the playback head of the combined unit and to the the playback control head and the correction unit are connected, and the output is connected to the inputs of the playback amplifiers with adjustable and fixed gain factors, the first and second inputs of the playback channel switch are connected to the output of the playback amplifier with a fixed gain, respectively, through the third band filter

0 harmonics of the reference frequency and a series-connected attenuator and band-pass filter of the reference frequency, the first and second inputs of the channel selector are connected respectively to the output of the playback amplifier with adjustable gain and the switch of the playback channel, and its outputs are connected to the inputs of the oscilloscope, the timer is connected to the first and second keys The control unit is connected to the selector switch, the switch

0 playback channel, magnetic head selector, timer, recording channel switch, first, second, and third key through which the bias generator is connected to the recording channel switch.

FIG. 1 shows a block diagram of the proposed device; in fig. 2 — graphs of temporal dependencies of voltages at various points of the device; in fig. 3 - waveform.

R. The device contains a tape-carrying mechanism 1, which provides transportation with a given constant speed of the magnetic tape ring. An erasing magnetic head 2, a control magnetic

5 reproducing head 3 and a test combination unit of 4 magnetic heads. A high-frequency voltage is applied to the head 2 from the erase generator 5 through the first key 6 by a value that ensures complete wiping of the waveform previously recorded on a magnetic tape. The recording head of the combined unit 4, depending on the mode of operation of the device, is powered from the biasing generator 7, the reference frequency generator 8,

5 of a high frequency generator 9, equal to the upper frequency of the operating range and the generator 10 of the reference level with a reference frequency. In this case, by changing the output voltage of the oscillators 8 and 9, the write current correction can be changed. The high frequency bias voltage is applied to the recording head of the combined unit 4 via the third key AND, the recording channel switch 12 and the key 13. The voltage from the recording generators 8, 9 and 10 is fed to the recording head of the combined unit 4 through the recording channel switch 12 and the second key 13. Switching the And key and controlling the operation of the switch 12 is carried out by signals from the control unit 14 depending on the mode of operation of the device. Switching keys 6 and 13 is carried out either by signals from the control unit 14 or by signals from timer 15, depending on the mode of operation of the device. At the same time, the control of timer 15 is also carried out from the control unit 14. The amount of current flowing through the recording head of the combined unit 4 is determined using a current meter 16. The monitoring of the measurement of parameters and the determination of some parameters is carried out from the image on the screen of a two-beam oscilloscope 17 Depending on the measured parameter at the input of the double-beam oscilloscope 17, a signal is reproduced by either the reproducing part of the combined head 4 or the control head 3. The signal reproduced by the head 4, depending on the parameter being measured, goes either to the first input of the double-beam oscilloscope 17 through the head selector 18, the playback amplifier 19 with adjustable gain, the channel selector 20, or to the second input of the double-beam oscilloscope 17 through the selector of the heads 18, amplifier playback 21 with a fixed calibrated gain, a channel of frequency selection, including a band-pass filter 22 of the reference frequency, an attenuator 23, a band-pass filter 24 of the third harmonic hydrochloric frequency channel reproducing switch 25, then through the channel selector 20. The signal reproduced by the head 3, is supplied only to a first input of a two-beam oscilloscope 17 through series-connected correction unit 26, bit selector 18, a reproduction amplifier. adjustable gain 19 and the channel selector 20. The device operates as follows. When measuring the rated bias current, the recording head of the tested combination unit 4 is supplied with currents from the reference frequency generator 8 and the high frequency generator 9, and the high frequency recording current is corrected relative to the reference current value depending on the type of magnetic tape used. The criterion of equality of the measured bias current to nominal is followed by the equality to zero of the amplitude-frequency characteristic of the recording at high frequency relative to the reference frequency with the corrected recording current of high frequency. For this purpose, alternating interconnected radio pulses with a reference frequency and a high frequency are recorded on a pre-demagnetized erasing magnetic head 2 magnetic tape. Radio pulses are formed by the switch 12 of the recording channel, switched by a command from the control unit 14 to the mode of automatic connection to the recording head of the tested combination block 4 of the generators 8 and 9 via the public key 13. The switch operation in this mode is explained in the time diagrams shown in FIG. 2a, 26.28. The digital index indicates the block number in the block diagram (Fig. 1). In addition, through the open by the same command from the control unit 14, the key 11, the switch 12 and the key 13, the biasing current from the generator 7 is constantly supplied to the recording head of the tested combined unit 4. The repetition of radio pulses in the mode of measuring the bias rated current is carried out to control reproduction magnetic head 3, connected to the measuring path by a command from the control unit 14 selector magnetic heads 18. The signal from the head enters the input of the first channel of the oscilloscope 17 through the coupled correction unit 26, the magnetic head selector 18, the reproduction amplifier 19 with adjustable gain and the channel selector 20 are connected. As a result, on the oscilloscope screen, in general, the oscillogram shown in FIG. 3. The coordinate grid scaled in decibels placed on the oscilloscope screen makes it possible to determine the difference in the levels of reproduced signals with the reference frequency and high frequency. With a change in the high frequency bias current, the difference in the level of the reproduced signals changes. The amplitude-frequency characteristic of the recording is determined by the expression of the AFC t. 6, d, where AFCS is the amplitude-frequency characteristic of the record; Ev.ch. EMF of the reproduced high frequency signal; EOCH. EMF of the reproduced signal of the reference frequency; DB is the rise of the amplitude-frequency characteristic of reproduction of the control magnetic reproduction head at high frequency relative to the reference frequency. The rated write current in the device is measured after determining the rated magnetising current. The criterion for the equality of the recording current to the nominal value is the equality of the nonlinear distortions of the set value in the pass-through recording-playback path at the rated bias current. At the same time, the EMF of the playback head of the tested combination unit 4 should not be less than the set value. In the mode of measuring the rated write current, the device operates as follows. On command from the control unit 14, the generator of the reference frequency and the reference level is connected to the recording head of the test combo unit 4 via the recording channel switch 12 and the key 13 instead of the generators 8 and 9, and the reference signal is written to the pre-demagnetized erasing magnetic head 2 frequency and reference level. For information processing when changing the nominal recording current, the signal reproduced by the playback head of the tested combination unit 4 is used. This head is connected to the measuring path using a selector of magnetic heads 18. Using the channel selector 20, a second channel of the measuring path is connected to the second input of the two-beam oscilloscope 17, consisting of a playback amplifier 21 with a fixed calibrated gain, a band-pass filter 22 of the reference frequency, an attenuator 23, a field the third harmonic filter of the third harmonic of the reference frequency and the switch of the playback channel 25. When the recording current changes, the value of the emf and the third harmonic coefficient at the output of the playback head, and therefore at the output of the playback amplifier 21, also change. The change of the recording current in the device should be carried out until the coefficient of the third harmonic of the reproduced signal reaches a specified value. At the same time, the control over the change of the third-harmonic coefficient is carried out visually in the device according to the image on the oscilloscope screen. This is implemented in the device as follows. The signal at the output of the playback amplifier 21 contains the component of the reference frequency, and, due to the non-linearity of the recording process, constitutes the third harmonic (Fig. 2 g, 2 d). With bandpass filters 22 and 24, these components are separated and then fed to the switch of the playback channel 25, and the component of the reference frequency enters the input of the switch through the attenuator 23. The attenuator 23, depending on the selected measurement mode, has a transfer coefficient: Where KJP is the third harmonic coefficient corresponding to the selected measurement mode,%. Switch 25 operates similarly to switch 12 and is also controlled by signals from control unit 14. As a result of the switch’s operation, a sequence of radio pulses with a reference frequency and the third harmonic of the reference frequency (Fig. 2e) acts on its output, and on the oscilloscope screen an image similar to that of FIG. 3. By changing the recording current, the amplitudes of the radio pulse bursts on the oscilloscope screen are equal. This corresponds to equality, 3F - 100 where UJF is the third harmonic voltage of the reference frequency; Up is the value of the voltage reference frequency; The CRR is the third harmonic factor value corresponding to the selected measurement mode,%, which is performed when the third harmonic factor of the reference frequency reaches the specified value. At this, the change in the recording current is stopped, the amplitude of the radio pulse pulses is monitored for the magnitude of the reproduction head EMF of the combined unit 4 at the reference frequency, which should not be less than the set rate. By a command from the control unit, the key 11 is closed, and the value of the nominal write current is determined from the current meter. The losses due to the reciprocal tilt of the recording and reproducing heads in the tested combination unit 4 are determined in the device by recording the high-frequency recording tape on the magnetic tape, then reproducing this recording with the reproduction head and aligning the combined unit 4 to the angle of inclination . In this case, during reproduction, the emf is measured before the adjustment and after the adjustment, which ends after the emf reaches its maximum value. The difference in electromotive force, expressed in decibels, will be the magnitude of the losses due to skewing of the underturning and reproducing heads in the tested combination unit.

The level of the penetrating direct signal at high frequency from the recording head to the playback head of the combined block 4 is defined as the difference, expressed in decibels, between the EMF at the terminals of the playback head induced by the penetrating signal and the EMF when the signal is played from the same frequency from the magnetic tape.

The invention can find wide application in the production of combined, universal and recording magnetic heads for both household and special magnetic recording equipment. The addition of a known device with a recording channel switch, timer, current meter, control unit, correction unit, magnetic head selector, channel selector, attenuator, playback channel switch, as well as the introduction of new connections between device units, allows for measuring four more basic recording parameters of combined magnetic heads, which are necessary to verify the parameters of magnetic recording apparatus with through channels record-playback th. Introduced in the automation device a number of basic operations of the parameter measurement process allows to eliminate the influence of the operator’s subjective factor on the measurement results and, consequently, improve the measurement accuracy in comparison with the known measurement methods using standard instruments by (10-15%). In addition, automating the measurement process reduces the measurement time by a factor of 1.5-2.

Claims (1)

DEVICE FOR MEASURING THE PARAMETERS OF A COMBINED MAGNETIC HEAD UNIT containing a tape drive, an oscilloscope, a playback amplifier with a fixed gain, a playback control head, test signal generators and electrical keys, characterized in that, in order to expand the functionality of the device, a head is inserted into it erasure, recording channel switch, magnetic head selector, playback channel switch, third-harmonic reference filter frequencies, a reference bandpass filter, erasure and bias generators, an attenuator, a channel selector, a timer, a correction unit, a variable gain amplifier and a control unit, the erasure head being connected to the erase generator via the first key, switch inputs. recording channels are connected to generators. test signals, and the output through the second key is connected to the recording head of the combined unit, the first and second inputs of the magnetic head selector are connected respectively to the playback head of the combined unit and to the playback control head and the correction unit connected in series, and the output is connected to the inputs of the playback amplifiers with adjustable and a fixed gain, the first and second inputs of the switch of the playback channel are connected to the output of the playback amplifier with ph respectively, through the third harmonic bandpass filter of the reference frequency and the attenuator and the bandpass filter of the reference frequency connected in series, the first and second inputs of the channel selector are connected respectively to the output of the playback amplifier with an adjustable gain and a switch of the playback channel, and its outputs are connected to the inputs of the oscilloscope, the timer is connected to the first and second keys, the control unit is in communication with the channel selector, the channel switch reproduce Nia, selector magnetic heads, a timer, a switch write channel, the first, second and third switches through which a bias generator coupled to the write channel switch.