Audio frequency oscillator

Fig. 40. Block diagram of measuring circuit. P, potentiometer L, load inductance R, small resistance D, dual scoper O, audio frequency oscillator A, sawtooth wave generator B, tuned amplifier K, oscilloscope equipped with amplifiers Q, gain control of cathode follower to read Q...

Wien bridge oscillator (audio frequency oscillator)... 

The circuit diagram of this probe is illustrated in Fig. 11.11. The high voltage DC/DC converter is on the upper half of the drawing. An audio frequency oscillator composed of three NOR circuits drives the base of Q102. The step-up transformer T1 is in the collector circuit of Q102, which is fed by the emitter follower Q101. 

Apparatus. All electrical resistances were measured with an electrolytic conductivity bridge (Leeds and Northrup model 4666) which was constructed according to specifications set forth by Jones (28) and described by Dike (29). The audio-frequency source was a General Radio Co. type 1311-A audio oscillator used with the frequency regulated at 1000 Hz and the output at about 5 V. The detector circuit consisted of a high-gain low-noise tuned amplifier and null detector (General Radio Co. type 1232-A) and an oscilloscope (Heathkit model O-ll) ... 

The crystals are placed between the plates of a condenser which forms part of an oscillating circuit. An audio-frequency amplifier, with headphones or speaker, is connected to the oscillator. When the frequency of the oscillator is changed continuously by means of a variable condenser in the circuit, clicks (or, for a large number of small crystals, rustling noises) are heard. The reason is that whenever the frequency of the oscillator happens to coincide with a natural frequency of one of the crystals, there is a sudden change of current through the condenser and consequently an impulse which is amplified by the audio-frequency amplifier. For a suitable circuit see Wooster (1957). 

These two examples show that Av is very much smaller for homonuclear double resonance, suggesting a simple way to generate v2. Instead of using a separate rf oscillator, we can use part of the output from the v, channel electronically modulated with an audio-frequency signal to generate output at v2. This technique makes it easier to control the exact value of Av and to focus v, and v2 exactly where we want them. 

Sound Velocity Method. Kundt s tube, complete with speaker unit (miniature cone or horn driver) and movable piston holding microphone stable audio oscillator, preferably with calibrated dial small crystal microphone oscilloscope audio-frequency amplifier, to be used if scope gain is inadequate electrical leads rubber tubing stopper thermometer. 

Figure 14.13 shows the time domain waveform and spectrogram of a creaky door hinge. The door sound starts off with some relatively slow pops as initial sticking and slipping takes place (0.0-0.22 s), followed by a silent period, then more rapid pops (0.4-0.6 s) followed by an audio-rate oscillation that sweeps upward in frequency (0.6-0.68 s), settling in a relatively stable oscillation (0.7-1.2 s). A little silence is followed by more quasi-periodic creaky oscillation. This system and vibration is much more complex than the relatively simple oscillation of the bowed prayer bowl, but it is still produced by a stick/slip physical mechanism. The prayer bowl, the door, and many other stick/slip oscillation systems can be simulated using the relatively simple bow table model. 

All P.M.R. spectra were measured with a Varian HA 100 spectrometer operating in the frequency-sweep mode with tetramethylsilane as the reference for the internal lock. The double and triple resonance experiments were performed using a Hewlett Packard 200 CD audio-oscillator and a modified Hewlett Packard 200 AB audio-oscillator (vide infra). Spectra were measured using whichever sweep width was required to ensure adequate resolution of the multiplets under investigation, generally 250 or 100 Hz, and sweep rates were selected as necessary. Extensive use was made of the Difference 1 and Difference 2 calibration modes of the instrument, both for the decoupling experiments and for the calibration of normal spectra. 

Figure 1. Circuit diagram showing a fine-frequency control for a Hewlett-Packard 200 AB Audio-oscillator.

The electrodes were powered by an audio amplifier whose input frequency was set by an audio oscillator. The impedance of the chamber, 6 Q, was perfectly matched to the output impedance of the amplifier. To test the proper functioning of the apparatus before putting in mammalian cells, we used the common bacterium Escherichia coli. These, and prokaryotic cells generally, do not show mitotic figures in division. After the bacterial population reached a steady state, the electric field was turned on. The density... 

Facilities for a variety of multiple-resonance experiments, including broad-band, homo- or hetero-nuclear decoupling, are now generally built into the spectrometer, instead of being provided by auxiliary audio-oscillators. Oscilloscopes for optimization of magnetic-field homogeneity, precalibrated recorder-charts, and frequency counters for accurate calibration of charts and frequencies for multiple... 

Simultaneous with the publication of Hocker et al., there appeared the results of Yardley and Moore [142] on laser-excited vibrational fluorescence in CH4. A mechanically chopped He-Ne 3.39-micron laser [143, 144] was used to excite the asymmetric stretching [/ = 2948 cm-1 (36.55 X 10-2 eV)] vibration, i>3 (see Figure 3.17). The optical arrangement is shown in Figure 3.18. The He-Ne laser tube, 220 cm in length, is shown on the left. Mx, M2, and Ms are mirrors Bx and B2 are baffles to eliminate stray light Lx and L2 are lenses which focus the laser output into a collimated beam having a diameter of 2 mm, and thence, into a Pyrex fluorescence cell. At the focal point between Li and L2 is a chopper wheel, to produce a nearly perfect square wave modulated at frequencies between 600 and 10,000 Hz. An audio oscillator and a 60-W amplifier are used to drive the synchronous chopper motor. An InSb infrared detector (response time of about 4 nsec) is used to... 

This experiment is based on a modified version of Kundt s tube, in which the wavelength X of standing waves of frequency /are determined electronically. Figure 3 shows the experimental apparatus, which utilizes an audio oscillator driving a miniature speaker as the source and a microphone as the detector. Also, an alternative apparatus based on a small spherical resonator has been described by Colgate et al. ... 

The thickness of a polymer extrudate can also be measured ultrasonically. In this type of measurement, the sensor uses mechanical vibrations of high frequencies, beyond the audio range, i.e. more than about 15,000 vibrations per second. The vibrations are produced by a transducer, which converts the electrical output of an oscillator to ultrasonic vibrations of corresponding frequencies. 

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