| 摘要 |
FIELD: measurement technology. SUBSTANCE: piezoelectric converter of acoustic emission has case, base, two piezoelements, two matching transformer, fastening member and cable. Bass is manufactured in the form of elongated composite rod composed of part in the form of disc having diameter, part with gradually narrowing section and part in the form of rod having diameter. Piezoelements are mounted on face surface of disc of base. Electrodes of first piezoelement are electrically insulated from base. First piezoelement is made of piezoceramic material with Curie temperature pointless than maximum temperature Tof object. Second piezoelement is fabricated in the form of ring with axial polarization and electrodes on face surfaces. First transformer is put inside case and second transformer is located beyond limits of object. Primary winding of first transformer is electrically connected to first piezoelement, cable couples electrically secondary winding of first transformer and primary winding of second transformer. Secondary winding of second transformer is connected to next path of amplification-conversion equipment. First transformer is designed on base of ferrite ring with Curie temperature point lower than maximum temperature of object. Cable includes two shields isolated from each other, one of them is electrically connected to base and grounded, the other one is electrically connected to upper electrode of second piezoelement. Base is put of object with the help of fastening member. Fastening member and base are manufactured as unit. Fastening member is fabricated in the form of threaded stud and rod of base rests against object with at least part of face surface. Dimensions of piezoelements and minimal resonance frequency fof converter are chosen from conditions, where Dis diameter of disc of base; Dis diameter of rod of base Dis diameter of first piezoelement; c is sound velocity in material of base; fis minimum frequency of mechanical waves radiated by object; fis maximum frequency of mechanical waves radiated by object; L is length of rod of base; Tis maximum temperature of object; Tis Curie temperature point of material of first piezoelement; α= 0.6-1.5 mm/C is empiric coefficient; fis minimum resonance frequency of converter; His height of second piezoelement; His height of first piezoelement. Thanks to shape and ratios of dimensions temperature less than Curie temperature point of low-temperature piezoceramics having high values of piezomodules is provided on face surface of disc of base. Simultaneously minimal reflections of acoustic signal are ensured. First piezoelement operates under mode of reception of acoustic emission and second one is used to test serviceability of converter. EFFECT: increased sensitivity, diminished brokenness of frequency characteristic of converter. 8 cl, 2 dwg |
