Strobe light tachometer
When the flicker frequency of light coincides with the speed of any object, such as a fan, the rotating fan may appear to be stationary. Changing the frequency of the flicker of light may help detect the rotation speed.
You may easily use the flicker frequency control buttons to quickly assign the flicker frequency with an accuracy of 0.01Hz (1 RPM):
• Up to 1000 Hz (60 000 RPM) for a connected flashlight (see the video on YouTube).
IF THE SPEED IS MORE THAN UPPER LIMIT, YOU MAY STILL DETERMINE THE SPEED BY FIRST MAKING MEASUREMENTS WITH A LOWER FLICKER FREQUENCY AND THEN MAKING A SIMPLE CALCULATION (AS EXPLAINED IN THE APPENDIX).
To change the frequency, you should simply press and hold the button. The flicker frequency can be displayed either in Hz or RPM.
The image you see will be sharper in lower external light.
After a long period of usage, in case of overheating, the iPhone flashlight turns off automatically.
Connecting a flashlight
Follow these guidelines:
Connecting a high-powered light requires more complex circuitry. However, the circuit design is still simple enough for a beginner. The key point is to pick a light with a focusing lens (a zoom lens).
In the video, the first light produces 2000 lumens (according to the seller), and the second one produces 1000 lumens. Both lights support several modes of operation (high and low power, as well as flashing at various frequencies). The switching between modes occurs when the light is quickly turned off and back on. For this reason, to avoid changes of mode during the operation of the stroboscope, a resistor is used to close the light's circuit. Before using the stroboscope, one needs to set the light into the full power mode by opening its circuit as shown in the video. In order to be able to pick the correct mode it is important to remember the order in which modes are activated.
Follow these guidelines:
Do not buy a laser pointer with small batteries (button cells), because you will "go broke" buying batteries.
Without soldering iron and multimeter
Measurement of rotational speed by stroboscopic tachometer
To determine the rotational speed (e.g., to determine the fan rotation speed), a plane perpendicular to the axis of rotation should be visible, and only one mark should be on this plane. For example:
You should begin measurements from the largest frequency that is possible for the tested fan. To reduce the flicker frequency, simply click and hold the button.
The observed pattern will change. For example, if the actual speed of the fan is 1100 RPM, and you began measuring the flicker frequency at 4400 RPM, then as you reduce the flicker frequency, the following still images will appear:
Four or three marks can be seen at other flicker light frequency; for example, three fixed marks can be seen at a flicker frequency of 1650 rpm (real RPMs multiplied by 1.5), four marks at a flicker frequency of 1466 rpm (real RPMs multiplied by 1.333.) and five marks at a flicker frequency of 1375 rpm (real RPMs multiplied by 1.25).
The wrong conclusion can be made when defining the RPMs by increasing the occurrence of the flicker frequency of the flash. For example, at a flicker frequency of 367 rpm (real RPMs divided by 3), one mark is visible:
This frequency can be misleading, since after multiplication or division of this reading by 2, one may obtain the same pattern as what is observed at the correct frequency (in this case, at 1100 RPM). Therefore, you should not start with a small flicker frequency and then increase it.
After determining the speed of rotation, you can save your readings by taking a photo with the result of the measurement written on it.
Calculating a speed of rotation that is higher than upper limit
When the speed of rotation is more than upper limit, it may be calculated by using a simple formula. Let us take an example where the actual rotational speed is 11000 RPM. When you decrease the flicker frequency of light from 6000 RPM, you should determine the frequency at which it is possible to observe a single fixed mark for the first time:
This occurs at a frequency of 5500 RPM (F1). With a further reduction of the frequency, the reading at which one fixed mark can be observed will be at 3667 RPM (F2). And the next time it happens, it will be at 2750 RPM (F3). A calculation is then performed by using two adjacent measurements:RPM = (F1 • F2)/(F1 – F2)
RPM = (F2 • F3)/(F2 – F3)
This method can also be used when the speed of revolution less than upper limit. When the standard way was used, some difficulties occurred (e.g. when the approximate rpm is not available).
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