Frequency ranges, accelerometers

One application is the accelerometer, in which the acceleration force of a mass is made to increase (or decrease) the pressure produced on the crystal by a spring. This, in turn, produces the required electrical change, the effect of which is amplified. It is important to select units appropriate for the expected changes, which should be within the frequency range from almost zero to the natural frequency of the crystal. 

The acoustic sensor used for capturing process vibrations is often a standard accelerometer, covering a frequency range 0-50 kHz - or a so-called acoustic emission sensor (AE) often covering higher frequencies from 50 kHz up to several MHz. The 4396 and ATEX 5874 accelerometers from Briiel Kjaer are shown in Figure 9.2. The 4396 accelerometer is a standard accelerometer for industrial use and the ATEX 5874 is a certified accelerometer for use where explosion proof equipment is needed (EX certified). 

The frequency range over which accurate data may be obtained is bounded, on the lower end, by the frequency response characteristics of the force gage and accelerometers, and on the... 

Accelerometers generally fall into two application categories of impact or motion measurements. The specifications for each type of application vary with regard to sensitivity, zero-g offset, frequency range and noise. In all cases there is a desire to have the smallest possible package size and lowest power consumption. 

The si/e of mass within the accelerometer determines the self-resonant frequency of the sensors. The smaller the mass, the higher the frequency Accelerometers are usually operated in a range below this self-resonant, freqncnc)/. 

The effective range of general-purpose accelerometers is from about 1 Hz to 10,000 Hz. Ultrasonic accelerometers are available for frequencies up to 1 MHz. In general, vibration data above 1000 Hz, or 60,000 cpm, should be taken and analyzed in acceleration or g s. 

The effective range of general-purpose accelerometers is from about 1 Hertz to 10,000 Hertz. Ultrasonic accelerometers are available for frequencies up to 1 MHertz. 

In order to construct a magnitude and phase vs. frequency plot of the transfer function, the nondimensional time will be converted back to real time for use on the frequency axis. For the conversion to real time the following physical variables will be used po = 1350 kg/m, b = 15 p.m, and /Hf = 0.85 mPa/sec. The general frequency response is shown in Figure 64.4. The flat response from DC up to the first corner frequency establishes this system as an accelerometer. This is the range of motion frequencies encountered in normal motion environments where this transducer is expected to function. 

Above these frequencies the range of AE measurement in rock begins with applications in mines as well as in laboratory studies. In the frequency region of about 1 kHz up to 100 kHz accelerometers or typical piezoelectric AE sensors are used in mines. The t5q)ical distances between sensors may amount up to 50 m the covered areas may have linear dimensions of up to 200 m. 

All thermal actuators have a reputation of being rather slow, due to thermal time constants typically in the upper millisecond range, particularly for the cooling phase. Large forces can usually be achieved at the expense of considerable power consumption. In small structures, however, it has been shown that substantially higher speeds can be attained, due to reduced thermal time constants. Thus, an accelerometer based on a thermally actuated resonant read-out principle was shown to operate at a frequency of 400 kHz [308],... 

Due to its robustness. PVDF has found application as an accelerometer (3334). Piezoelectric polymer aoceleroineteis have high sensitivity, low-frequency operation, large dynamic range, excellent linearity, high resonant frequency, low mechanical quality foctors (Q ), low transverse sensitivity, and small temperature dependence. 

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