Stroboscopic measurements

A stroboscope is a device that allows intermittent observation of cyclically moving objects so as to create an optical illusion of stopped or slowed motion. By controlling the frequency of intermittent vision, it is possible to replace fast real movement with slow forward or backward movement (if the frequency of flashes is higher than the rotation frequency, then it is an apparent backward movement and vice versa) and thus observe, analyze, or photograph every detail of the movement.

The flashes of the strobe lamp are electronically controlled and precisely adjustable. The light source is a xenon lamp or LEDs. High-quality stroboscopes also have external synchronization, usually via a 3.5 mm jack input (signal, e.g. 5 to 30 V rms). These stroboscopes usually also have an output for synchronizing another stroboscope. In this way, it is possible to achieve illumination of a larger area.

Areas of use of a stroboscope

Speed measurement – when the frequency of flashes is equal to the frequency of rotation, the movement appears to stop (measurement accuracy up to approximately 1%). If the flash frequency is an integer fraction of the rotational frequency, a simple stationary image can be seen. If the flash frequency is an integer multiple of the rotation speed, more stationary images will appear, e.g. if the flash frequency is 2 times the rotation speed, two images 180° opposite each other will appear, if 3 times the rotation speed, 3 images 120° apart, etc. (see Fig. 1).

Measuring shaft speeds from the side – drawing a strip around the shaft with a break in one place and a line at a right angle to this break. A simple stationary image of this place will be visible at the speed frequency and its subharmonics. At a flash frequency higher than the speed, a cross of these two lines will be visible (see Fig. 2).

Vibration measurements

- measuring vibration frequency by apparent stopping of movement. By adding a length (angle) scale, it is also possible to obtain information about deflection (torsional oscillation). Possibility to observe slow motion, this way, for example, the behavior of fans, belt drives, shafts, aircraft propeller blades, helicopter rotors, oscillations in the area of elastic mountings of internal combustion engines, etc. can be studied.

- detection of resonant regions using a shaker (in "sine sweep" mode). The frequency of the flashes must be controlled by the shaker excitation frequency using an external signal input on the strobe. By setting a small offset, it is possible to watch even slow motion. By doubling the frequency of the flashes, it is possible to make the extreme positions of the part in resonance visible.

- misalignment indication, detection of critical rotor speeds, etc.

Measurement of mechanical slip – measuring the speed difference between the drive shaft and the belt-driven device - taking into account the gear ratio (slip caused by the belt). In case of greater slippage (over 5%), the belt wears out faster. Belt tension also affects the noise level of rolling bearings.

Measurement of linear velocities - discs for measuring the speed of movement of belts of belt drives are often accessories of stroboscopes. It is a nylon disc with a known circumference, marked with a radial stripe. The disc is pressed against the moving belt and from its revolutions measured with a stroboscope, the speed of the belt movement can be determined (see Fig. 3). Similarly, it is possible to measure the surface speed of drums, wheels, rollers, pulleys, etc.

List of used literature:

[1] corporate materials of Lutron Electronic Enterprise

Internet sources:

[1]? https://youtu.be/0JXCw5pOecg?feature=shared

Stroboskopické merania

Stroboskop je zariadenie, ktoré umo?ňuje preru?ované pozorovanie cyklicky sa pohybujúcich objektov tak, aby sa vytvorila optická ilúzia zastaveného alebo spomaleného pohybu. Riadením frekvencie, ktorou je preru?ované videnie, je mo?né nahradi? rychly reálny pohyb spomalenym pohybom dopredu alebo dozadu (ak je frekvencia záblezkov vy??ia ako frekvencia otá?ania potom je to zdanlivy pohyb dozadu a naopak) a tak pozorova?, analyzova?, ?i fotografova? ka?dy detail pohybu.

Záblezky stroboskopickej lampy sú elektronicky riadené a presne nastavite?né. Zdrojom svetla je xenónová vybojka alebo LED diódy. Kvalitné stroboskopy majú i externú? synchronizáciu,? zv???a prostredníctvom? 3,5 mm? jack? vstupu? (signál napr. 5? a? 30 V rms). Tieto ?stroboskopy? majú potom oby?ajne aj vystup na synchronizáciu ?al?ieho stroboskopu. Tymto sp?sobom je mo?né dosiahnu? osvetlenie v???ej plochy.

Oblasti vyu?itia stroboskopu

Meranie otá?ok – ke? je frekvencia záblezkov rovná frekvencii otá?ania dochádza ku zdanlivému zastaveniu pohybu (presnos? merania pribli?ne do 1%). Ak je frekvencia záblezkov celo?íselnym podielom otá?kovej frekvencie je mo?né vidie? jednoduchy stacionárny obraz. Ak je frekvencia záblezkov celo?íselnym násobkom otá?ok, objaví sa viac stacionárnych obrázkov, napr. ak je frekvencia záblezkov 2-násobkom otá?kovej frekvencie objavia sa dva obrázky 180° oproti seba, ak 3-násobkom 3 obrázky po 120° a pod. (vi? obr. 1).

Meranie otá?ok hriade?ov z bo?nej strany – nakreslenie pásu okolo hriade?a s preru?ením v jednom mieste a ?iary v pravom uhle v tomto preru?ení. Jednoduchy stacionárny obraz tohto miesta bude mo?né vidie? pri otá?kovej frekvencii a jej subharmonickych. Pri frekvencii záblezkov vy??ej ako je otá?ková bude vidie? krí? z tychto dvoch ?iar (vi? obr. 2).

Vibra?né merania

- meranie vibra?nej frekvencie zdanlivym zastavením pohybu. Pridaním stupnice d??ky (uhla) je mo?né získa? aj informáciu o?vychylke (torzné kmitanie). Mo?nos? sledova? i spomaleny pohyb, takto m??e by? ?tudované napr. správanie sa ventilátorov, remeňovych prevodov, hriade?ov, listov leteckych vrtú?, rotorov vrtu?níkov, kmitanie v oblasti pru?ného ulo?enia spa?ovacích motorov a pod.

- detekcia rezonan?nych oblastí vyu?itím ?ejkra (v re?ime ?sine sweep“). Frekvencia záblezkov sa musí riadi? pod?a frekvencie budenia ?ejkrom prostredníctvom vyu?itia externého vstupu signálu na stroboskope. Zaradením malého offsetu je mo?né sledova? i spomaleny pohyb. Zdvojnásobením frekvencie záblezkov je mo?né zvidite?ni? extrémne polohy dielu v rezonancii.

- indikácia nesúosovosti, detekcia kritickych rychlostí rotorov a?pod.

Meranie mechanického sklzu – meranie rozdielu otá?ok medzi hnacím hriade?om a remeňom poháňanym zariadením - so zoh?adnením prevodového pomeru (sklz sp?sobeny remeňom). V?prípade v???ieho sklzu (nad 5%) dochádza k?rychlej?iemu opotrebovaniu remeňa. Napnutie remeňa ovplyvňuje aj úroveň hlu?nosti valivych lo?ísk.

Meranie lineárnych rychlostí - príslu?enstvom stroboskopov byvajú aj kotú?e na meranie rychlosti pohybu remeňov remeňovych prevodov. Ide o nylonovy kotú? so známym obvodom, ozna?eny radiálnym pásikom. Kotú? sa pritla?í ku pohybujúcemu sa remeňu a z jeho otá?ok meranych stroboskopom je mo?né ur?i? rychlos? pohybu remeňa (vi? obr. 3). Podobne je mo?né mera? i povrchovú rychlos? bubnov, kolies, valcov, remeníc a pod.