Stroboscope / Stroboscope Light

A stroboscope light is a piece of equipment that can make a rotating, reciprocating, oscillating or vibrating object appear still. This is referred to as a stop-motion effect. If a moving object appears to be stationary when observed with a stroboscope, then the stroboscope is attuned to the vibration frequency of the object.

An industrial stroboscope light is a measuring instrument commonly used to inspect stresses on different machine parts in motion. For example, an industrial stroboscope light can be used in a print shop to evaluate the rotational speed of a printer roller. Thus, an industrial stroboscope also can be used as a tachometer to count the number of revolutions or measure the revolutions per minute (RPM) of a cyclically moving part.

Before purchasing an electronic industrial stroboscope light, one must consider the intended application. An electronic stroboscope can reach a flash rate of several thousand Hertz, making it possible to carry out optical inspections for very fast sequences. Therefore, the stroboscope's flash rate must accommodate measurement of the rotors, gears, cams, shafts, spindles, etc. to be inspected.

In addition to the adjustment of the flash rate or flash frequency, modern stroboscopes also offer the possibility of setting a phase shift. This means that the flash pulse is delayed in such a way that the picture optically rotates. This makes it possible to move the marking brands on the rotating parts into a correct position.

A key factor to evaluate when buying an electronic stroboscope light is the type of light source used by the strobe. Modern light-emitting diode (LED) stroboscopes have nothing in common with the conventional Xenon flashers. In modern LED stroboscopes, powerful LED arrays enable comprehensive illumination of an object. Due to the scalability of the LED stroboscopes, even large parts like moving paper webs can be inspected with ease. For certain non-destructive testing applications, special stroboscopes that utilize ultraviolet (UV) LEDs may be required.

The trigger of the luminaire is another important component of the stroboscope light. Simple stroboscopes have internal regulators to control the LED luminaires or xenon tubes. Triggering from outside is not possible in these stroboscope light designs. More complex stroboscopes are equipped with trigging inputs that allow external speed sensors to control the luminaires. Thus, the flashing of the stroboscope is always equal to the number of revolutions or oscillations of the object. This is particularly advantageous when different rotational speeds of rollers are driven. This is the case especially in the sphere of paper production or during the testing of printed products.

In the case of handheld stroboscopes, the decisive factor is how the power supply is performed. Here it is of crucial importance how often the stroboscope is used. If the handheld stroboscope is used sporadically, a battery power supply is often sufficient. If the handheld stroboscope light is used frequently, a rechargeable battery power supply is recommended. Fixed installation stroboscopes are generally supplied with an AC power adapter or powered directly from the mains.

When acquiring a stroboscope, one should also think about the ingress protection (IP) rating required for the application. The IP rating or class specifies whether a device is dustproof or waterproof. If a stroboscope light will be used in harsh industrial conditions, an IP67 rating is recommended for optimal protection against external environmental influences.

The animation makes it clear what possibilities of optical analysis and inspection you have when using the stroboscopes, whether in the production of the process recordings (video of the process on the machine or the sequence of tests in research and development) or during the purely optical inspection in everyday work in the factory. Usually the stroboscope light has an external trigger input and trigger output. So, as desired, you can adapt the flash frequency to the respective process or trigger the rotating or moving part or the part to be assessed, with the help of the stroboscope light.

The stroboscope can be used very well when the process you want to see has to do, for example, with splashing water or other liquids. The stroboscopes flash the process in a split second. PCE Instruments has many years of experience in this field (since 1999). The various stroboscopes can be synchronized with the film cameras of all leading manufacturers to create professional, commercial film recordings. However, some camera models require a modification of the device interface in order to fit the stroboscopes exactly. We are happy to assist you with technical questions.

Below you may find an example of an illustrated report on the use of a stroboscope light. The versatility of the stroboscopes has been demonstrated on a paper machine (as well as other applications in various other industries). The article appeared in the weekly newspaper for the paper production:

PCE Instruments uses stroboscopes in paper mills
Because the economic conditions are forcing many factories to downsize their technical departments, it is becoming increasingly important to provide the existing personnel with those tools that can help to assess the process quickly and accurately. One type of these tools is a stroboscope, with which you can not only measure the rotational speed, but also determine frequencies and detect pulsations. Thus, stroboscopes are universally usable auxiliary tools for the assessment of the conditions on machines with rotating systems and for the visualization of events. The stroboscope light creates still images that make the things, which would otherwise remain hidden from the human eye, recognizable.

In many cases (in addition to the application of the stroboscopes by their own factory staff), such devices are used by the well-known machine manufacturers and external consultants for quality control.

"The stroboscopes of the PCE series are particularly valuable for the assessment of the flat web processes. With these devices the causes for wet edges / tips on the Fourdrinier sieves can be detected very well," says Mr. Vielhaber, one of the engineers, who knows the devices well from his own experience. "The stroboscope is light – one is very mobile with it and can act well in the most hidden corners." In addition to assessing the quality parameters, the stroboscopes make it possible to measure the rotational speed of, for example, belt-driven systems and to check the synchronism in multi-belt operation quickly and precisely. The stroboscope light is often used to determine the rotor speed of, for example, ventilation systems (fans).

Analysis of the sieve section
Especially in the case of very wide fourdrinier sieves, the powerful stroboscopes of the PCE series make it possible to assess the entire web width. For example, the assessment of the water line (water level) and its pulsations is an important criterion for the functionality of the headbox and the spindle. Take a look at the drainage below the sieve and the scraping water on the suction bars. The "still picture" created with the help of the stroboscope light gives you conclusions about the drainage process. Or assess the volume and evenness of the spray mist.

The stroboscope is ideal for evaluating the sieve section, ”says Mr. Vielhaber,“ Defects in the sheet formation can be recognized very well and, for example, can be traced back to pulsations.

Monitoring the synchronism of the performance rope
Of course, the stroboscopes can also be used very well to assess the synchronism of the performance ropes. The rope wear is very high when there is a difference in speed. The service life of the ropes decreases significantly. It is also difficult to come back to normal after the paper web has come to a standstill or torn off. The stroboscope light makes a differential speed directly visible. In this way, one may carry out targeted checks group by group. The picture shows how easy it is (coating system area). However, when using the stroboscopes, always pay attention that they are not applied near the light barriers or demolition detectors. This would have annoying consequences.

Stroboscope PCE-1XS
These mains-operated stroboscopes are mostly used for long-term observation, for example, the analysis of the jet exit at the headbox with different settings of jet-sieve ratio, or the point of impact of the jet on the screen table. The jet shape (constriction) and uniformity is very clear with the help of the stroboscope light. The entire width of the headbox can be viewed. If this particularly powerful stroboscope is positioned, for example, on the driver's side next to the breast roll, the scraping water of the roll can be also very well seen.

The stroboscope PCE-1XS is also used for the continuous inspection of the product in the steel roll mills. The detection of defects on the material surface is very easy, for example, when pressing in the particles that adhere to the press rollers. These recurring pressings can then be easily traced, because the distance between the defects on the steel roll can be traced back to the roll circumference. Thus, you know exactly which roller or which pair of rollers caused the pressing. The extreme luminosity of these stroboscopes is particularly optimal for such shiny or reflective surfaces. The smallest faults are recognizable.

On labeling machines in the brewery or printing house, the use of mobile, battery-operated or mains-operated stroboscopes is also very useful. Bring the print image to a standstill and just optically assess the accuracy of the fit and the process. Check the product properties, for example, after changing roles or after retrofitting, for example, the unrollers. The full web width can be inspected, up to 1.2 m. The machines do not have to be brought to a standstill.

Steel Production
To observe moving objects, especially when they are moving at high speeds, and control various dynamic processes is not easy, because the smallest details cannot be caught by the eye. Application of a device that creates a kind of optical illusion of a stable/frozen image significantly facilitates this task.

Stroboscope illumination finds its application in many spheres, from the entertaining purposes or photography to serious industrial tasks. “Motion blur effect” is a real problem when it is necessary to observe some process over a certain period of time or detect faults on some object, and this problem can be solved with the help of the stroboscope illumination. The effect which it the stroboscope creates is the absence of movement and the image becomes much clearer, and the defects – more visible.

Stroboscopes applied for the continuous or long-term monitoring of the industrial processes, in particular, steel production, can be installed permanently, so called fixed mounting. By adjusting the stroboscope for the measuring task correctly, it is possible to achieve the accurate monitoring and the optimal illumination of the area/object under control. Depending on the flash frequency, different effects may be created: the steel surface moving forward, backwards or being stable in the production line.

Correctly selected frequency ensures that all the defects in the structure of the surface can be recognized. Depending on the type of steel in the production, the surface may have different level of “roughness”. The frequency of the flashes must be selected correspondingly. Analysis of the pattern on the surface allows making conclusions about the condition of the equipment in the conveyor, for example, shafts engaged in the steel production.

The frequency over 70 Hz sometimes applied for stainless steel does not make the illumination brighter, it helps to create a clearer image. On the contrary, excessive amount of illumination does not make the detection of the defects easier, and stroboscope light is as a rule sufficient or should be much brighter than the illumination coming from the other sources. An interesting fact about stroboscope is that the total amount of time, when the lamp is on, is very small, but the effect achieved is that an operator may clearly detect the fault and even determine the type of it.

Observation of the steel production is a long and monotonous process which requires a lot of concentration. Fixed mount stroboscope is a significant facilitation, since it helps an operator to see the clear image instead of a constantly moving surface and blurred image. In the case of the industrial production, and significant amounts of the material / products, a failure to notice the defect timely leads to serious consequences, like production of big batches of the spoilt or bad-quality product. Application of the fixed mount stroboscope light helps to determine either the defect is repeatable or of an occasional character. This helps to detect the location of the problem and thus eliminate it timely.

Polygraphy
Though many industrial processes are fully automated nowadays, it does not always guarantee the top-quality and absence of any mistakes and defects. Their detection after the termination of the production process does not allow any correction, and often means nothing but a confirmation of the defect of the whole batch. It implies extra-costs, loss of time and often creates a negative impression about the quality. Monitoring of the production process in real time serves to prevent the faults and their repletion during the whole process of production.

An operator responsible for monitoring is not able to ensure the 100% accuracy, since the quickly moving line, for example in polygraphy, cannot be taken by the eye as a stable image and the motion blur effect is a serious obstacle. In the industrial processes when it goes about paper production or polygraphy quality is one of the most important criteria.

Correctly adjusted frequency of the light pulses, from one side, does not create any discomfort for the eye of the operator and from the other – allows detecting the defect on the paper produced or mistakes during printing. Occasional faults may indicate problems with the equipment, breaks of the paper web, unexpected folds, problems with the rolls and many other reasons which in the long run lead to a poor quality and paper defects. In the event of timely detection of the problem, it is possible to quickly correct the problem and let the process continue further in the optimal way.

Application of the fixed mount stroboscope light is an effective way to reduce the risks of mistakes made by the operator, which in its turn means improvement of the printing process in general. Even if the defects happen because of the problems in the printing machines or poor paper quality, they also can be detected with the help of the stroboscope light within a short time period. Modern stroboscopes installed for the monitoring of the production process can work together with the cameras, able to produce a big amount of shots.

The frequency of pulses is high, but energy consumption is very low, and this cost-effective factor is also one of the pros which is favorable for any modern enterprise, since by reducing the running costs the efficiency of the production is increased. Maintenance of the production on the highest possible level helps to save a lot of time, arrange the production in the best way and also win a good reputation and create a reliable and strong connection with the customers and suppliers.

The stroboscopic effect causes certain localized periodic movements not to be perceived as they actually occur. This effect occurs when we do not perceive a continuous image, but rather individual images that follow each other quickly at short intervals. If these single images always show the same content, it appears as if there is no movement. If the cycle, i.e. the time interval between the individual images, is greater than the period of the motion, but not an integer multiple, the rotation or oscillation appears to be slowed down.

If the time interval of the individual image (frame) is shorter than the rate of the movement, the latter not only appears to be slower, but it appears as if the observed part is moving in the opposite direction. Sometimes this apparent reversal of the direction of motion can be seen in movies, for example, spinning car wheels or machine parts, because the speed of rotation does not match the number of frames per second. In the movies for entertainment, the effect plays a rather minor role. In films and videos for demonstration and explanation of processes, however, care should be taken to ensure that the direction of movement is correct so that the processes are not misinterpreted.

Rapid movements can be optically slowed down or brought to a standstill by using the stroboscopic effect. In order to create the strobe effect in a targeted manner, it is necessary to allow the view of the object to be observed only at regular intervals. This is usually achieved by specifically timed illumination.

For this purpose, the devices have been developed that emit short flashes of light the time interval of which can be adjusted. With such a stroboscope light, it becomes possible to assess abnormalities in motion sequences that otherwise cannot be detected because of their speed. In addition, rotational or oscillatory speeds can be measured without contact by adjusting the rate of the light flashes on the stroboscope so that it matches the rate of the movement.

The stroboscope light effect can also be used for targeted show effects at concerts, in discos or in theatres. On the other hand, it can be caused unintentionally by the regular flickering of certain artificial light sources. This can lead to hazards in work spaces due to the incorrect assessment of machine movements. In addition, perceptible constant flickering can also lead to visual disturbances, discomfort and headaches.

Therefore, when designing lighting, care should be taken not only to ensure that there was enough light for the use of the room, but always to ensure that it functions as flicker-free as possible. Flickering in certain frequency ranges may be particularly harmful to epileptics. The optical stimulation can trigger an epileptic seizure. For this reason, special attention is often drawn to this risk when stroboscopic effects are planned.

A trigger is generally a direct or indirect initiation of a process or reaction. External triggering means that the signals are not generated within the excited system. External trigger signals act randomly or purposefully from outside.

In a stroboscope light with a trigger input, for example, the frequency of the light flashes can be synchronized with the speed or the cycle of the machine under inspection. For this purpose, electronic signals are generated in or on the machine, tapped and transmitted to the stroboscope light via the trigger interface. The stroboscope then transmits the light flashes in the cycle specified by the machine.

Many stroboscopes lights offer additional functions to specifically adjust the trigger signals.

These functions include:

• the delay of the signal in milliseconds,
• the delay related to the phase angle
• the factor or division.

The time delay and phase angle can be used to generate the light flashes exactly when the object under consideration has reached the desired position. For example, the temporal delay can be set with values between 0 and 1,200 milliseconds, and the phase angle can be set with values between 0 and 359 degrees. The factor, on the other hand, can be used to multiply the triggered clock.

In some stroboscope lights, the trigger interface can be used not only as an input for trigger signals but also as a signal output. The cycle stored in the stroboscope as a flash frequency can be transmitted via the trigger output to the machines that allow this. This makes it easy to set the devices used together in a line to the same cycle.

A stroboscope does not measure directly, but it is important for the application that the frequency shown on the display corresponds to the actual timing of the flashes of light. A calibration can be used to determine the deviation between the displayed frequency and the actual frequency. Stroboscopes are usually calibrated using frequency counters.

The frequency counter used as a reference during the calibration must have a higher accuracy than the tested stroboscope. In addition, the reference itself must also be calibrated regularly. Otherwise the results of the check are meaningless. When calibrating, it is not the light flashes emitted by the stroboscope that are registered with the frequency meter, but the signals from the internal clock generator.

A stroboscope is usually checked for three or more measuring points. Anyone who orders a calibration should pay attention to how many and which frequencies the comparison is carried out for. For each measuring point, the frequency set in the stroboscope and the frequency determined by the reference device are noted in the calibration certificate. The actual deviation results from the difference between the two values. This numerical value is then compared with the allowable tolerance specified for the stroboscope or the desired tolerance.

If the numeric values for frequency are not displayed in the same unit, one of the two values must be converted to the unit of the other. If it is determined during the calibration that deviations are outside the permissible values, the stroboscope may only be used with restrictions. High-quality stroboscopes often have an adjustment function that can be used to set the clock correctly again.

In research and science, high-quality stroboscopes are used to observe and evaluate the cyclic movements. The stroboscope can be used to optically "freeze" the movements or to stimulate certain reactions. The stroboscope is also often used in conjunction with endoscopes, microscopes or high-speed cameras for better visual representation of rapid motion sequences.

Video microscopy with the stroboscope
In order to record fast movements or recurring sections of these movements with high image quality on video, the object can be illuminated with the stroboscope during the recording. Due to the repeated short flashes of light at the right time, the current phase of the movement can be recorded with very high detail. Previous and subsequent positions are in darkness and are therefore not visible. The camera's sensor only detects the object when it is illuminated. The other phases of the movement are therefore not superimposed on the image. The prerequisite for this optical freezing of the motion with the stroboscope is the tuning of the duration and frequency of the light flashes to the beat of the motion.

Stroboscopes and quantum computers
Among the important steps on the way to quantum computing is the creation of systems of multiple entangled quanta. Photons can be used very well for this purpose. Physicists from Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics have developed a method to generate multiple entangled photons simultaneously. To do this, a special stroboscope had to be used to generate ultra-short, high-energy flashes of light at the highest possible rate.

The research group led by Professor Harald Weinfurter achieved this by using a method, that works well in the infrared region of the light spectrum, for the first time for the more energetic UV region. The physicists let the UV light flashes lasting only a few femtoseconds ("femto" stands for 10 to the power of minus fifteen, "milli" for ten to the power of minus three) circulate at the very high clock rate of 82 megahertz in a resonator in such a way that the light pulses overlapped each other exactly. This method greatly increased the light intensity and also brought completely new fields of application to the attention and the field of vision of quantum physicists. For example, the method opens up new possibilities in optical spectroscopy.

The research group's paper was published online January 31, 2010, in Nature Photonics under the title "Ultraviolet enhancement cavity for ultrafast nonlinear optics and high-rate multiphoton entanglement experiments."

Neuroscience application for the stroboscope
Researchers at the University of Birmingham, Ruhr University Bochum and Emory University Hospital in Atlanta have found that acoustic stimuli, as well as stroboscopes, can set the oscillations in the brain to a specific rhythm. The findings were published online June 6, 2019, in a review article in the journal “Trends in Neurosciences”. Research based on this will include investigating how different frequency ranges of brain oscillations are related to memory performance and what therapeutic potential targeted rhythmization of the brain activity holds.

Stroboscopes in the medical diagnosis
At the ENT specialist, a special stroboscope can be used to visualize the oscillations of the vocal cords. The stroboscope used is a medical endoscope with a flash light source and magnifying optics. The timing, length and frequency of the light flashes can be adjusted on the stroboscope to produce a slow-motion recording of vocal cord vibrations. These images enable targeted diagnosis of the functional vocal cord disorders, profound inflammation and malignant changes.

In addition to research, the fields of engineering also include the development, design and optimization of machines, devices, methods and processes. In many processes with fast or periodic movements, stroboscopes can be used as an aid. The stroboscope can be used to make visible individual sections of the movement that would otherwise be imperceptible or barely perceptible. Whether inspecting existing equipment or testing new developments, the stroboscope can make the movements appear to slow down and even optically stop for the observer by appropriately timed brief illumination.

Since these visual inspections are carried out while the machine is running, the causes of anomalies and irregularities can be detected and eliminated much more quickly than when the machine is at a standstill. Not only for direct on-site inspections, but also for image and video recordings for documentation purposes, a stroboscope can contribute to significantly better recognition of details. This happens on the one hand due to the increase of the sharpness of photos by very bright short flashes and on the other hand due to the video recordings of extremely fast movements as slow-motion recording.

However, the stroboscope does not only improve the possibilities of visual control. Stroboscopes can also be used to measure the rotational speeds and clock frequencies. Device types with trigger function can also be used to precisely coordinate the machines in a drive train or production line. One of the machines sets the speed. The speed of the other is then matched to this speed so that the process runs as optimally as possible.

Paper production
In the paper industry, the stroboscope is often used to monitor and increase the efficiency of the production lines. It is not only used to measure the speed of rolls. The stroboscope is also useful for setting and checking the spray nozzles and for observing the sheet formation on the screens. Stroboscopes for applications in the paper industry are usually selected so that the complete web width of a roll can be checked in one go.

Printing plants, textile industry
As in paper production, the stroboscope can also be used in the printing and paper industry to examine work processes more closely. Whether it is a question of quality deficiencies on existing production lines or the adjustment of a new system, the stroboscope greatly simplifies the evaluation of the current processes and results on the machines.

Machine and vehicle construction
When testing newly developed or adapted vehicle or machine parts, there are many possible applications for the stroboscope:

• optical slowing of fast movements,
• slip measurement on belts and clutches,
• control of the synchronism of drives,
• non-contact speed measurement,
• observation of valve movements and injectors,
• monitoring of vibration amplitudes,
• measurement of vibration frequencies.

LED light sources and xenon flash tubes each have both advantages and disadvantages as a light source for a stroboscope. In order to find a suitable stroboscope for the intended applications, it is good to know the main differences between the two light sources. In many applications for the stroboscope, both types of illuminant are generally suitable. Then close attention should be paid to the respective specifications when making a shortlist. For some requirements, however, there is a clear favorite in terms of the illuminant or even exclusion criteria for the other type of the illuminant.

The following sections list some important characteristics in which LED and xenon lighting differ.

Flash duration
A stroboscope with a short flash duration allows clear sharp images even of the objects moving very fast. It can be used not only for visual inspection, but also for high-speed photography. Units with xenon flash tubes produce light flashes that are only one to twenty microseconds long. Strobes with LED bulbs, on the other hand, provide flashes from five to a thousand microseconds long, depending on the model. Some devices offer the option of setting different flash lengths.

Amount of light per flash
The amount of light describes the luminous flux emitted by a light source over a certain period of time. An ordinary LED stroboscope produces a light quantity of 0.08 lumen seconds with a flash duration of 20 microseconds. In contrast, the stroboscope with a common xenon flash tube emits 67.50 lumen seconds with the same flash duration, thus more than eight times the amount of light. High light quantities ensure strong brightness and thus very good image sharpness.

Flash stability
The stroboscopes with LED technology emit far more uniform flash sequences than the stroboscopes with xenon lamps. This makes them more suitable for high-speed or slow-motion shots. Motion that occurs within one second can be recorded as many individual images and played back later at a slower rate. Delayed playback reveals the details that are otherwise imperceptible.

Light colour and colour rendering
Where it is important that the colours of the object under examination are correctly reproduced, the stroboscope with the xenon flash tube is clearly the better choice. The colour accuracy of the stroboscope with the LED illuminant is lower, because LEDs emit light of a narrow wavelength range only. The colour accuracy of the LED stroboscopes is indicated by the colour rendering index. Often this index is below 90, but for the better coloured LEDs the colour rendering index is stated > 90 in the specifications.

Infrared and UV light stroboscopes
In the stroboscope with LED as illuminant, the wavelength range of the emitted light is much narrower than in the stroboscope with Xenon flash tube. If infrared or UV light is required for certain applications, the stroboscope with xenon illuminant or with special LEDs must be used. The stroboscope with xenon illuminant can emit light flashes with both visible and broadband UV light. When using LED as illuminant, on the other hand, several stroboscopes are needed if both normal and UV light tests are to be performed.

Tabular comparison of LED and xenon light for stroboscopes