Weak current College】 【】 pressure sensor.

<br> Some direction along a dielectric strength and mechanical deformation (squeezing or extension), its internal polarization phenomenon will occur, and in some of its surface will have a charge. When the external force removed, it will return to the uncharged state, .this phenomenon is called "the piezoelectric effect". Commonly used piezoelectric materials with natural piezoelectric crystals (such as quartz crystals) and piezoelectric ceramics (such as barium titanate), their pressure motor mechanism is not the same, piezoelectric ceramics is synthetic polycrystalline, piezoelectric .constant high than quartz crystal, mechanical properties and stability than quartz crystal. They all have good characteristics, are ideal for piezoelectric material. <br> Piezoelectric pressure sensor is the use of piezoelectric materials of piezoelectric effect will be converted to electrical signals measured pressure. .By piezoelectric material piezoelectric pressure effect of charge volume and forcing linear relationship between: <br> Q = kSp <br> Q-in-charge; k for piezoelectric constant; S p for the role of area; to pressure. By measuring the amount .of electric charge measured pressure size unknown. <br> Figure 1 is a piezoelectric pressure sensor structure diagram. Piezoelectric trapped between two elastic diaphragm, piezoelectric components of a side and the diaphragm and grounding, the other side by the leader will charge the amount of .leads. The role of the measured pressure evenly in the diaphragm, the piezoelectric force and charge. Charge for general use charge amplifier or voltage amplifier, converted to a voltage or current output, the output signal and the measured pressure corresponds to the value. < .br> In addition to the standard in the calibration of pressure sensor or high accuracy pressure sensor using quartz crystal do piezoelectric, piezoelectric pressure sensor of piezoelectric materials for piezoelectric ceramics, but also useful for polymeric materials (such as poly unsymmetrical dimethyl fluorine second rarly) .or composite synthetic membranes. <br> <br> Figure 1 piezoelectric pressure sensor structure diagram <br> Replace the piezoelectric element can change pressure measuring range; with charge amplifier, it is possible to use multiple piezoelectric component parallel manner to improve the sensitivity of .the sensor; in equipped with voltage amplifier, it is possible to use multiple piezoelectric inline manner to improve the sensitivity of the sensor. <br> Piezoelectric pressure sensor is small, simple structure, reliable working condition; measurement range, the pressure measured 100MPa following .; higher measurement accuracy; frequency response up to high, is the dynamic pressure 30kHz testing common sensor, but because of the existence of a piezoelectric element, so the charge leakage is not suitable for slow change of pressure measurement and static pressure. <br> .<br> Diaphragm-type resonator pressure sensor <br> Diaphragm type pressure sensor structure figure (a) below. The diaphragm is a flat diaphragm, and the overall structure of the shell into the ring, and base constitute sealed pressure measurement Chamber, the .measured pressure p after import pressure pipe into pressure measuring indoor. Reference pressure Chamber can pass the atmospheric pressure is used to measure the table, or drawn into absolute pressure of vacuum measurement. Mounted to base at the top of the solenoid as shock vibration source to .diaphragm provides exciting force, when the vibration frequency and patch natural frequency, the diaphragm has resonance. No pressure, the diaphragm is flat, its resonance frequency f0; when there is pressure, mechanical deformation of the diaphragm, the tension increases, the corresponding resonator .frequency is increased, the frequency with the pressure change and a function for a single value. <br> <br> In the patch on a strain gage, it can output a resonance frequency of the same signal. This signal amplifier, then back to .the exciting coil to maintain continuous vibration of the diaphragm, which constitute a closed-loop positive feedback self-excited oscillation system. Figure (b) as shown in <br> <br> Vibration drum resonance pressure sensor <br> Vibrating cylinder pressure sensors .are pressure components is a thin-walled metal cylinder, the cylinder itself has a natural frequency, when wall subjected to tension, the stiffness of the changes, the natural frequency be changed. At a certain pressure, changes in the frequency of vibration drum can .approximate expressed as: <br> <br>-Fp for compression of the frequency of the vibration of cylinder; natural frequency f0 to; a coefficient for structure; p is the pressure being measured. <br> The sensor consists of a vibrating cylinder .Assembly and excitation circuit, shown in Figure 3-14 shows. Vibration drum with low temperature coefficient of constant elastic material, one end closed to free-to-end, open end fixed in base, pressure from the inside. Insulating bracket fixed with exciting .and measuring coils coil, both spatial location mutually perpendicular to reduce electromagnetic coupling. Exciting coil enable vibration drum by inherent vibration frequency, the frequency variation before and after compression can be checked out by detecting coils. <br> This kind of instrument volume small, .the output frequency signal, repetitive, vibration-proof; high precision, the accuracy of ± 0.1 and ± 0.01%; suitable for use in gas measurement. <br> <br> Vibrating cylinder pressure sensor <br> <br>.