The use of ultrasound in machine diagnostics

Ultrasound is sound waves with a frequency above 20 kHz. Today it is used in many areas among other things also in machine diagnostics. The short-wave nature of the ultrasound signal provides various advantages from the point of view of diagnostics, such as early detection of even small changes in the controlled system, quick localization of problem areas facilitated by the directionality and low energy of such radiation, etc. Ultrasound propagates in solid substances, liquid and gaseous medium. When measuring ultrasound in air an ultrasound microphone is used. It can be used e.g. for detecting leaks (in pressure and vacuum systems), electric sparking, etc. Piezoelectric or MEMS sensors are used in the field of structural detection of places associated with ultrasound generation. From this field (structural detection) the use of ultrasonic methods is known e.g. in case of problems with lubrication or friction, early detection of damage to rolling bearings (see e.g. [A], [B]), faults in drives, transmissions, etc. As for the available measuring technology for route measurements is used e.g. Inspector 400 (from SKF), for automated measurements it can be a measurement system equipped e.g. with ultrasonic sensor UCA 586 (see pictures no. 1 and 2).

In the field of monitoring the operation of machinery the introduction of ultrasonic measurements allows to significantly expand the predictive capabilities of the system. When identifying problems with lubrication (various friction nodes), damage of rolling bearings it is possible to use trend characteristics or analyze time courses and spectra. In the initial stage of faults it is possible to detect changes especially in the time domain. For this reason time analysis is preferred over spectral analysis in ultrasound analyses.

Another area of use of ultrasonic measurements can be EoLT systems in cases where conventional vibrodiagnostic methods do not allow reliable identification of a certain problem (e.g. the occurrence of disturbing sounds in connection with friction, etc.) and thus the differentiation of OK and NOK product.

This is an important area of technical diagnostics, which is also confirmed by the creation of technical standards in the field of ultrasound measurements. For example the international standard ISO 29821 solves the issue of ultrasonic monitoring of machine condition.

List of used literature:

[1] corporate materials of SKF, UE SYSTEMS INC.

Internet sources:

[A]? OK bearing? ?????https://youtu.be/ISj9bth3Uds?feature=shared

[B]? NOK bearing? ???https://youtu.be/8AmSHMg43so?feature=shared

The ultrasounds for the OK and NOK bearing sensed by the instrument were converted (“heterodyning”) into the audible range.

Vyu?itie ultrazvuku pri diagnostike strojov

Ultrazvuk je zvukové vlnenie s?frekvenciou nad 20 kHz. Dnes sa vyu?íva v?mnohych oblastiach, okrem iného i? pri diagnostike strojov. Krátkovlnny charakter ultrazvukového signálu poskytuje z?h?adiska diagnostiky r?zne vyhody,? ako je napr. v?asné zachytenie u? malych zmien v?kontrolovanom systéme, rychla lokalizácia problematickych miest u?ah?ená smerovos?ou a?nízkou energiou takéhoto vy?arovania a?pod. Ultrazvuk sa ?íri v?tuhych látkach, kvapalnom i?plynnom prostredí. Pri meraní ultrazvuku vo vzduchu sa pou?íva ultrazvukovy mikrofón. Je ho mo?né pou?i? napr. na detekciu netesností (v tlakovych a vákuovych systémoch), elektrického iskrenia a?pod. V?oblasti ?trukturálnej detekcie miest spojenych s?generovaním ultrazvuku sa pou?ívajú piezoelektrické alebo?MEMS senzory. Z?tejto oblasti je známe vyu?itie ultrazvukovych metód napr. pri problémoch s?mazaním resp. trením, v?asnej detekcii po?kodení valivych lo?ísk (vi? napr. [A], [B]), chyb pohonov, prevodov a?pod. ?o sa tyka dostupnej meracej techniky na poch?dzkové merania sa vyu?íva napr. Inspector 400 (od firmy SKF), pre automatizované merania to m??e by? merací systém vybaveny napr. s ultrazvukovym senzorom UCA 586 (vi? obrázky ?. 1 a 2).

V?oblasti monitorovania chodu strojnych zariadení umo?ňuje zavedenie ultrazvukovych meraní vyznamne roz?íri? prediktívne schopnosti systému. Pri identifikácii problémov s?mazaním (r?zne trecie uzly), po?kodením valivych lo?ísk je mo?né vyu?i? trendové charakteristiky alebo analyzova? ?asové priebehy a?spektrá. V?po?iato?nom ?tádiu chyb je mo?né zachyti? zmeny najm? v??asovej oblasti. Z?tohto d?vodu sa pri ultrazvukovych analyzach uprednostňuje pred spektrálnou analyzou najm? analyza v??ase.

?al?ou oblas?ou vyu?itia ultrazvukovych meraní m??u by? i?systémy EoLT v?prípadoch, ak be?né vibrodiagnostické metódy neumo?ňujú spo?ahlivú identifikáciu ur?itého problému (napr. vyskyt ru?ivych zvukov v?súvislosti s?trením a?pod.) a?teda odlí?enie OK a?NOK vyrobku.

Ide o?vyznamnú oblas? technickej diagnostiky, ?o potvrdzuje i?tvorba technickych noriem v?oblasti ultrazvukovych meraní. Problematike ultrazvukového monitorovania stavu strojov sa venuje napr. medzinárodná norma ISO 29821.