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1、- E I A 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 Copyright Electronic Components, Assemblies where fc is the freque
2、ncy of the reference 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
3、reproduced reference 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 Band
4、pass Filter, Flutter 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
5、 a rate of 18 dB per 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
6、152.4 60 0.5 to 10,000 609.6 240 0.5 to 10,000 304.8 120 0.5 to 10,000 - _ - Copyright Electronic Components, Assemblies but, may additionally contain discrete components. In order to mea- sure this signal adequately statistical techniques shall be used. 4.7.1 Acceptance Tests (Cumulative Flutter) T
7、he 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 must be within the value read 95 percent
8、of the time. I t 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 known that the flutter sig- nal follows
9、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 oscilloscope may be used as an indicator for
10、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. The simulated flutter signal shall be obta
11、ined 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 percentage of modulation shall be accurately d
12、etermined and compatible with the anticipated flutter O Y am pli tu de. Copyright Electronic Components, Assemblies 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, “Informa
13、tion Transmission Modulation and Noise” 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,
14、for predicting additive noise in a 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 ran
15、dom function plus some discrete periodic 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 show
16、n in Fig. 2. The spectrum analyzer 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
17、spectrum is time-varying (random or 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 usua
18、lly termed power spectral density (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 sta
19、tisti- cally independent spectra which are averaged. Copyright Electronic Components, Assemblies 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 AMPLITUDE MO DU LATO R I I I I I I I I I I I D ISCR I MI NATO R FLUTTER- BAN
20、 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 Copyright Electronic Components, Assemblies & Materials Association Provided by IHS under license with ECA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 19:54:20 MDTNo reproduction or networking permitted without license from IHS -,-,-