Crystal controlled oscillators

In the measurement technique, which has been used on D3 for many years, the ratio of the time spent counting with the cryoflipper in (+) or (-) mode is controlled by a quartz crystal controlled oscillator with a highly stable output frequency / of 1 MHz. There are two scalers to count the detector pulses (+ and - states), a single monitor scaler and a single time scaler used to end the measurement when the total time is reached (precision of 1 ms). 

Texas Instruments (1981) SN74LS320 crystal-controlled oscillators, D2418, 3-801... 

This is the heart of the microcomputer. The CPU or microprocessor examines the contents of memory and interprets them as instructions or data. The way in which the processor interprets the numbers stored in memory depends on the design of the chip, that is, on the manufacturer. This is the machine code and the microprocessor s repertoire of arithmetic and logic functions is called its instruction set. The CPU is connected to the memory by two sets of wires called the data bus and the address bus. The data bus is used to transfer data to and from the memory. The address bus is used to identify that part of memory with which the processor wishes to communicate. It is important that the processor and the memory act in a synchronized manner. All microcomputers contain a crystal-controlled oscillator which acts like a metronome to which all actions are synchronized. This oscillator is sometimes referred to as the clock. 

The accuracy with which elapsed time can be measured is rarely a limitation in modern instruments. The frequency of the AC power lines is of sufficient accuracy in most locations, except for very short times (less than a few cycles). If higher precision is needed, and for battery-operated instruments, a timer based on a crystal-controlled oscillator is capable of precision to better than 1 part per million. Sufficient accuracy for many purposes can conveniently be obtained from the time-base of a strip-chart recorder on which the detector response is plotted. Older instruments depended on a hand-held stopwatch or other mechanical or electromechanical device. 

Crystal-controlled oscillator An oscillator in which a piezoelectric-effect crystal is coupled to a tuned oscillator circuit in such a way that the crystal puUs the oscillator frequency to its own natural frequency and does not allow frequency drift. 

The Beech capacitance indicator utilizes the current-curve characteristics of a crystal-controlled oscillator. The indicator assembly is an all-transistorized unit with a self-contained power supply for the amplifier and the oscillator circuits. The circuit incorporates the use of semiconductor capacitors in place of the usual mechanical capacitors in order to eliminate any tendency for the unit to change tuning due to vibration. 

FIGURE 3.3 Block diagram of a crystal-controlled oscillator circuit for a RF power supply. 

Time interval standards. The familiar, though expensive, electronic wrist watches are clearly time interval standards since they are read in seconds, minutes, and hours. Yet at the heart of the watch is a crystal-controlled oscillator operating at a frequency of 1 MHz so the lucky owner also possesses a personal frequency standard of quite respectable quality. Having made the point that time and frequency standards are basically identical, we recall that for many centuries our methods of determining time intervals have relied on sub-division of a basic standard the length of the day as measured on earth (see Table 18.4). In the... 

Digital timers of excellent quality that are based on crystal oscillators are available. The resonant frequency of such oscillators is temperature dependent and subject to aging effects, but the state of the art is highly developed. Crystal-controlled clock oscillators having a maximum error of 1 ppm at 25°C are commercially available from a number of manufacturers. Some units are tem-... 

A 1- to 2-kW radio frequency power supply, either free-running or crystal-controlled, drives current through a water- or air-cooled copper tube that acts as the induction coil (often called a load coil). The oscillating current through the load coil produces an oscillating electromagnetic field. 

Quartz (silicon dioxide) crystals are used for piezoelectric crystals for radiofrequency control oscillators and digital watches and clocks. 

For that purpose, the quartz crystal is simultaneously excited at two frequencies. The response at the lower frequency is processed by a feedback loop dedicated to measure and automatically compensate Cq. The response at the higher frequency is processed by a phase-locked loop that continuously maintains and tracks oscillations at/s. The voltage waveform V hl is the sum of the two sinusoidal signals V h. with frequency/h generated by the voltage controlled oscillator VCO, and Vl, with frequency/, lower than/n, generated by the auxihary oscillator OSC. The frequency/r of the signal Vu is taken as the output frequency/out of the whole circuit. In the frequency domain, the ex-... 

Figure 23.23 illustrates the most important experimental interface function, the generation of a stable time base. The time-base generator, or digital clock, is generally a combination of two elements (1) a crystal-controlled, stable, fixed-frequency oscillator that emits a pulse train of very accurately known frequency, and (2) a... 

To achieve this there is a hi-stab crystal controlled 20 MHz reference oscillator in the synchroniser circuit that is summed phase-coherently in the mixer with the step recovery diode output containing the 20MHz beat to produce the correction signal. 

The various oscillators differ mainly in the feedback process used. The two main types of oscillator used in plasma spectrometry are free running and crystal controlled . 

The active element of the electrochemical quartz crystal microbalance (EQCM) was a gold-coated quartz crystal whose oscillation frequency was equal to 5 or 6 MHz. It was plated in a similar way, but the metal coatings were thinner (0.2-0.4pm). The constant relating the variations in quartz crystal mass with its oscillation frequency was determined by special calibration using EQCM data obtained in acid CuSO solutions at a controlled current density. 

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