Operating frequency

The first example refers to the detection of a 1mm side drilled hole at a depth of 45 mm in a polyethylene plastic material. Due to the high sound absorption in plastics, a low operating frequency is chosen. A probe having a 1 MHz element of 24 mm diameter was selected for this example. The echo pattern of a conventional probe with a PZT transducer is pre-... 

A basic choice is that of operating frequency. In principle, operation can take place at any frequency at the cost of suppression of electromagnetic leakage to regulatory limits on RFI, eg, 25 ]lV/m at 304 m. This cost is avoided, however, by operating within assigned ISM bands. Minimum cost results in bands of considerable use where components are readily available. In the United States, these popular microwave bands are 915 and 2450 MH2. 

It is deeided that the power supply will operate at an operating frequency of 100 KHz, and the controller IC will be an MC34025R... 

The oseillator frequeney is set by referring to a timing graph. In order to provide a 100 kHz operating frequency, the values for RT and CT are... 

The eddy current loss is a much smaller loss than the hysteresis loss, but increases significantly with the operating frequency. It is shown in Equation 4.7. 

The advantages of a quasi-resonant converter over a classic PWM converter are smaller size and typically higher efficiencies. Although when a smaller size is pursued by increasing its operating frequency, the improvement in efficiency is sacrificed due to other frequency dependent losses. 

I have ehosen the maximum operating frequency of the power supply to be 250kFIz. At light loads, the maximum on-time should be in the order of 10 to 15 percent. So, the resonance frequency will be around 250kFIz as well. Solving for the resonant inductor. 

The minimum operating frequency of the control IC is set by the combination of the R and C on the oscillator pin. First one select the oscillator capacitor from a graph. The discharge period to produce a 200 kHz period (5 qS) can be produced with a 200 to 300 pF capacitor. Make Cose = 220 pF. The oscillator resistor is calculated from... 

The maximum operating frequency is set by additional discharge current being drawn by the error amp through resistor Rvfo. The equation to determine the additional discharge current (Imax) is... 

The peak eurrent within the primary eireuit is 3.1 A, whieh will oeeur at low-line and at a 200 to 400 kHz operating frequency. Then the output current from the secondary of the current transformer is... 

Next determine the maximum elosed-loop gain eross-over frequency. Less than one-fifth of the switehing power supply s operating frequency is a good rule. 

Electronic instrumentation is available for the measurement of D.C. and A.C. voltage, current and power as well as impedance. Such instruments usually have higher sensitivities, operating frequencies and input impedance than is normally found in the electromechanical instrumentation described above. However, they may need to incorporate amplifiers and they invariably need power to operate the final display. Hence, an independent power source is needed. Both mains and battery units are available. The accuracy of measurement is very dependent on the amplifier, and bandwidth and adequate gain are important qualities. 

Process or heating plant may have controls ranging from manual operation with some processes supervised by interlocks to semi-automatic and fully automatic operation. Deciding factors will include temperature of operation, frequency of ignition, degree of operator supervision, and rating of the plant. For example, boiler plant, both steam and water, will invariably have automatic control whereas tunnel kilns operated continuously at high temperature are unlikely to require it. 

It would normally be necessary to locate more than one monitoring unit on a structure. Thus each unit will only transmit its information on receiving coded instructions. Surface units can commonly accommodate up to 80 different codes. The ability to interrogate and receive over any distance is dependent upon the acoustic operation frequency. Relatively high frequencies are preferable, as they avoid problems of pulse reverberations and echoes from structural members. Typically data can be transferred over a distance of 2 km. This type of acoustic unit gives accuracies in potential measurement of 10mV. 

By using a system of measurement in which NMR absorptions are expressed in relative terms (parts per million relative to spectrometer frequency) rather than absolute terms (Hz), it s possible to compare spectra obtained on different instruments. The chemical shift of an NMR absorption in 8 units is constant, regardless of the operating frequency of the spectrometer. A H nucleus that absorbs at 2.0 8 on a 200 MHz instrument also absorbs at 2.0 8 on a 500 MHz instrument. 

Chemical shift (Section 13.3) The position on the NMR chart where a nucleus absorbs. By convention, the chemical shift of tetramethylsilane (TMS) is set at zero, and all other absorptions usually occur downfield (to the left on the chart). Chemical shifts are expressed in delta units. 5, w here 1 5 equals 1 ppm of the spectrometer operating frequency. 

Delta scale (Section 13.3) An arbitrary scale used to calibrate NMR charts. One delta unit (5) is equal to l part per million (ppm) of the spectrometer operating frequency. 

Operation Frequency Resolution Limit Penetration Depth... 

Although NMR spectrometers of operating frequencies > 400 MHz are cosdy and require specialist technical support staff, the technique provides a broad picture of the chemical modifications arising from the reactions of free radicals or related oxidants in complex, multicomponent systems such as intact biofluids, tissue sample... 

The transducers operate at a fixed frequency of irradiation emitting radiations through a fixed area of irradiation. Thus, the type of transducer coupled with the total area of irradiation and the operating frequency are the key factors in the efficient design of the sonochemical reactors. The three main types of transducers are gas driven, liquid driven and electromechanical transducers out of which the electromechanical transducers are by far the most versatile and widely used. 

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