1、- EIA 405 72 3234b00 00b7850 8 ,- F -i. -2: rn O Flutter Measurement of 7 4 9 Instrumentation Magnetic Recommended Test Method For rn ec w IA STANDARD RS=405 December 1972 Engineering Department ELECTRONIC INDUSTRIES ASSOCIATION EIA 405 72 3234b00 00b785L T NOTICE EIA engineering standards are desig
2、ned to serve the public interest through eliminating mis- understandings between manufacturers and purchasers, facilitating interchangeability and improve- ment of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existenc
3、e of such standards shall not in any respect pre- clude any member or non-member of EIA from manufacturing or selling products not conforming to such standards, nor shall the existence of such standards preclude their voluntary use by those other than EIA members whether the standard is to be used e
4、ither domestically or internationally. Recommended standards are adopted by EIA without regard to whether or not their adoption may involve patents on articles, materials, or processes. By such action, EIA does not assume any liability to any patent owner, nor does it assume any obligation whatever
5、to parties adopting the recommended standards. Published by ELECTRONIC INDUSTRIES ASSOCIATION Engineering Department 2001 Eye Street,N. W., Washington, D. C. 20006 Electronic Industries Association 1972 All rights reserved - Price $3.80 .- Prfnted in U.S.k - EIA 405 72 m 3234600 0067852 L m c-J RS-4
6、05 Page 1 RECOMMENDED TEST METHOD FOR FLUTTER MEASUREMENT OF INSTRUMENTATION MAGNETIC TAPE RECORDER/REPRODUCERS Q (From Standards Proposal No. 1123, formulated under the cognizance of EIA Working Group P-8.7 on Instrumentation Magnetic Recording Components where fc is the frequency of the reference
7、carrier, ff is the highest frequency flutter component to be measured, and a is the peak fractional flutter. If used, the filter response shall roll off at a rate of 18 dB per octave be- yond the cut-off frequencies. 4.4 Frequency Discriminator The discriminator must accept the reproduced reference
8、carrier which has been modulated by flutter and produce an output signal proportional to the modulation. In general, 60 dB amplitude limiting must precede the frequency-sensitive portion of the discriminator in order to meet the dynamic range requirements of the system. 4.5 Bandpass Filter, Flutter
9、A bandpass filter follows the discriminator. Its purpose is to limit the frequency band of the flutter signal and to reject carrier frequency components. The filter response shall be flat within 3 dB from 0.5 Hz to the upper flutter frequency being measured and shall roll off at a rate of 18 dB per
10、octave beyond the cut-off frequencies. Flutter bandpass filter characteristics: Tape Speed Passband of the Flutter cmls in/s Bandpass Filter (Hz) 2.38 15/16 0.5 to 156 4.76 1 7/8 0.5 to 313 9.52 3 314 0.5 to 625 19.05 7 1/2 0.5 to 1,250 38.1 15 0.5 to 2,500 76.2 30 0.5 to 5,000 152.4 60 0.5 to 10,00
11、0 609.6 240 0.5 to 10,000 304.8 120 0.5 to 10,000 - _- RS-405 Page 3 4.6 Magnetic Tape The tape shall be in excellent condition and of a type recommended by the recorder manufacturer. It shall be degaussed so that there will be no residual signal greater than 50 dB below the recorded carrier level.
12、4.7 hdicators and Analyzers The flutter signal from the bandpass filter foilowing the discriminator is a complex one which will, in general, be a random function; but, may additionally contain discrete components. In order to mea- sure this signal adequately statistical techniques shall be used. 4.7
13、.1 Acceptance Tests (Cumulative Flutter) The indicator used for acceptance tests shall be a direct-reading instrument designed to read the peak-to-peak amplitude and to ignore occasional random peaks provided that the value read is exceeded less than 5% of the time. That is, the peak-to-peak flutter
14、 must be within the value read 95 percent of the time. It is recognized that this measurement can be.made in several different ways. A block diagram describing one method is shown in Figure 1. Also, statistical voltmeters which accomplish this result are commercially available. Furthermore, if it is
15、 known that the flutter sig- nal follows a Gaussian amplitude probability distribution, the peak-to-peak measurement described above is four times the true rms value. 4.7.1.1 Frequency Response: 0.5 Hz to 10 kHz. 4.7.1.2 Averaging Time: 5 seconds. 4.7.2 Operational Tests (Cumulative Flutter) An osci
16、lloscope may be used as an indicator for operational tests. 4.7.2.1 Frequency Response: 0.5 Hz to 10 kHz. 4.7.2.2 Sweep Speed: O. 1 second per centimeter. 5. CALIBRATION OF TEST SYSTEM The flutter-measuring system shall be calibrated by simulating the flutter-modulated reproduced car- rier signal. T
17、he simulated flutter signal shall be obtained from a frequency-modulated oscillator, and shall consist of a sine-wave carrier frequency-modulated by a sine-wave modulating signal. The level of the modulated carrier shall be equivalent to that anticipated from the recrder/reproducer output. The perce
18、ntage of modulation shall be accurately determined and compatible with the anticipated flutter O Y am pli tu de. RS-405 Page 4 5.1 Accuracy i The system shall be accurate within +5% of full scale. 5.2 Frequency Response The frequency response of the system shall be uniform within 6 dB over the flutt
19、er bandwidth. 5.3 Noise Susceptibility I The system output noise caused by linear addition of the output noise of the tape recorder/reproducer system and a stable reference carrier at the same level as would be derived from the tape recorder/re- producer system shall be less than 5.0 percent of the
20、specified flutter. An alternative to this test is described in Appendix A. 5.4 Susceptibility to Amplitude Moduktion of the Carrier The system shall be subjected to an amplitude-modulated sine-wave carrier at the same level as would be derived from the tape recorder/reproducer system. The sine-wave
21、modulating frequency shall be varied from 0.5 Hz to the highest flutter frequency of interest. The level of modulation shall be 30 percent for modulating frequencies from 0.5 Hz to 1 kHz. For frequencies above 1 kHz the percentage of modulation shall vary inversely with frequency down to 3 percent a
22、t 1 O kHz. The system output noise for any single frequency shall be less than 5 percent of the specified flutter. 6. TEST PROCEDURE This test is to determine the magnitude of total cumulative flutter over a specified passband. Measure- ments are conducted at one or more points of tape-supply-reel l
23、oading for the specified tapespeed. Results are expressed as the peak-to-peak percentage change of a single recorded frequency during the reproduce process. 6.1 Connect the equipment as shown in Figure 2. 6.2 Adjust the precision signal generator and the discriminator to a carrier frequency suitable
24、 for the tape speed used. The frequency used should not be less than five times the maximum flutter fre- quency. (See Appendix A for recommendations regarding selection of carrier frequency.) 6.3 Place the degaussed tape on the machine, select the tape speed to be used, and place machine in RECORD m
25、ode. 6.4 Adjust record level, above normal to optimize the ratio of carrier-to-noise level, and minimum flutter. A value of approximately 13 dB above normal is suggested. CAUTION: Distortion can cause an apparent increase in flutter. When adjusting the record level of the carrier-frequency signal, t
26、he repro- duced signal into the discriminator should be monitored with respect to distortion. Many discrimi- nators are particularly susceptible to even harmonic and crossover distortion. 7 EIA 405 72 = 3234600 00b785b 9 A RS-405 Page 5 6.5 Record Test Signais 6.5.1 Acceptance Tests Record test sign
27、als on three tracks, two outside tracks and the center track. Record at three points: near the beginning, the middle, and the end of reel. Each record shall be 3 minutes mini- mum in length. 6.5.2 Operational Tests Record for at least three minutes record on one track.at any convenient point in the
28、reel. 6.6 Rewind the tape, place machine in REPRODUCE mode, and adjust carrier-bandpass filter and flutter-bandpass filter to the proper values for the tape speed used. (The reproduce speed shd be the same as the record speed.) 6.7 Read the peak-to-peak flutter output. 6.7.1 Acceptance Tests Observe
29、 the flutter on the indicator described in 4.7. 6.7.2 Operational Tests Observe the flutter as displayed on the oscilloscope at a sweep rate of O. 1 second per centimeter. The observation time shall be 5 seconds minimum. In reading the peak-to-peak amplitude, occa- sional random peaks which exceed t
30、he value read shall be ignored provided that the value read is not exceeded more than 5 percent of the time. A photograph of the oscilloscope trace may be used to supplement the visual observation. APPENDIX A SELECTION OF CARRIER FREQUENCY As shown in the following discussion, under certain conditio
31、ns, if the system parameters (carrier-to- noise ratio, carrier frequency and flutter bandwidth) are known, the error due to noise can be pre- dicted. The same equation can be used as a guide in selecting the carrier frequency. According to well-known fm theory the presence of noise at the input of a
32、n ideal discriminator results in an error-producing noise output. If the carrier-tenoise radio exceeds the threshold value, and if the noise is white noise, the magnitude of the error-producing output is: (1) EIA 405 72 W 3234600 00b7857 O RS-405 Page 6 where rms = output error due to noise in terms
33、 of fractional equivalent flutter. Nc/Sc = noise-to-carrier ratio in rms voltage; noise measured over a bandwidth of (f, -fm to (fo + fm). ff = Flutter bandwidth, Hz. fc = carrier frequency, Hz. For peak-to-peak readings on a 20: basis ( 1) Mischa Schwartz, “Information Transmission Modulation and N
34、oise” pp. 302-304, McGraw Hill Book Co., Inc., New York, N.Y. 1959. APPLICATION INFORMATION TESTS The operational and acceptance tests describe a procedure for measuring total cumulative flutter. For many applications this information is adequate; as, for instance, for predicting additive noise in a
35、 fre- quency-modulated recording system. However, for some uses more detailed information is necessary, for example, in predicting frequency distortion of recorded data. As mentioned in Paragraph 4.7, the flutter signal is generally a complex one consisting of a random function plus some discrete pe
36、riodic components. The most useful measurement of this signal is a spectrum analysis. . A spectrum analysis measurement of flutter follows the same procedure as used to measure cumulative flutter except that a spectrum analyzer is substituted for the indicators shown in Fig. 2. The spectrum analyzer
37、 is used to determine signal characteristics in the frequency domain. When the flutter signal contains discre te components the spectrum analyzer identifies the frequency and mea- sures the amplitude in the manner of a frequency-selective voltmeter. However, if the spectrum is time-varying (random o
38、r otherwise) a more suitable description is the spectral density. This may be expressed in terms of rms, or mean-squared amplitude per unit frequency (A/H2)lI2 or AL/Hzl , where A is an rms amplitude proportional to flutter. The mean-squared spectral density is usually termed power spectral density
39、(PSD). Averaging is required to obtain meaningful spectral density mea- surements. Since a statistically fluctuating parameter cannot be measured exactly, the measurement is termed an “es6mate”. The quality of the estimate improves in proportion to the number of statisti- cally independent spectra w
40、hich are averaged. _ I EIA 405 72 3234600 0067858 2 W RS-405 Page 7 There are several techniques available at this time which can be used in spectral analysis measurements. These can be classified in general terms as: Scanning-Filter - may have constant bandwidth filter or filter bandwidth may vary
41、with scanning frequency. Multifilter - consists of many parallel contiguous filters. Real-time - Analog and digital techniques are used to effect a “time-compression” of the data and decrease the analysis time by several orders of magnitude. F F T - An all digital technique using a computer which is
42、 programmed to implement the so- called fast-Fourier-transform. A detailed procedure for spectrum measurement is beyond the scope of this standard. However, some of the fundamental parameters which must be considered are: 1. Filter bandwidth (specify 3dB points, or “noise” bandwidth) 2. Scanning spe
43、ed (this is not within operator control on some instruments) 3. Averaging characteristics (may be in terms of normalized statistical error, E, or in degrees of freedom. If the output of a filter with bandwidth B is observed for T seconds this is expressed as 2BT “degrees of freedom” and the statisti
44、cal error is E = 1 /(BT)1/2. The output of the spectrum analyzer is given by typical indicating instruments such as meters, X-Y plotters, and oscilloscopes. A direct measurement of the effect of flutter on a recorded signal can be made by a spectrum mea- surement of the reproduced signal and observi
45、ng the sidebands produced by flutter. EIA 405 72 W 3234600 0067857 4 W RS-405 Page 8 c EIA 405 72 = 3234600 O067860 O RS-405 Page 9 I t I I I I I -r. v) -I o O I I I fl W d c EIA 405 72 m 3234600 00678bL 2 m _-. - VTVM ANDIOR OSCILLOSCOPE RS-405 Page 10 3 I - SIGNAL GEN E RATO R, 0.5 HZ - 10kHz - CA
46、 LI B RATED DISCR I MI NATOR FREQUENCY- MODULATED OSCILLATOR CARRIER- BAN D-PASS I I I FILTER I I I 1 I I I I NOISE SOURCE* SIGNAL CAR R I E R FREQUENCIES GEN E RATO R; VOLTMETER (TRUE RMS) LINEAR MIXING, C -o CAL I B RATED MODULATION (PERCENT) INDICATOR l. SIGNAL GEN E RATO R, 0.5 Hz to 10 kHz AMPL
47、ITUDE MO DU LATO R I I I I I I I I I I I D ISCR I MI NATO R FLUTTER- BAN D-PASS FILTER IN DI CATO R (S) I I I FLUTTER 1 I A I- I MEASURING SYSTEM SIGNAL GEN E RATO R, CAR R I E R FREQUENCIES *ACTUAL OR SIMULATED RECORDER/REPRODUCER NOISE SWITCH POSITION FUNCTION a b C Calibration of Flutter Amplitude NoiseSusceptibility Test AM-Susceptibility Test FIGURE 3 - SYSTEM TEST AND CALIBRATION
