Stroboscope |Mechanical stroboscope | Working | Construction | Advantages of stroboscope | Disadvantages of stroboscope | Limitations
Construction and working of stroboscope :
1)The stroboscope is a simple, portable manually operated device which may be used for measurement of periodic or rotary motions.
2) Basically, the instrument is a source of variable frequency flashing brilliant light, the flashing frequency being set by operator.
3) An oscillator is provided so that the moving object (target) is visible at specific intervals.
4) If strong light is caused to flash on moving object, the object will appear stationary.
5) The stroboscope consists of a source of flashing light whose frequency can be varied and controlled.
6) This source is called a stroboscope.
7) Stroboscope is hot cathode gaseous discharge tube.
8) It consists of one cathode, one anode and two grids.
9) Conduction starts when potential of outer grid is increased or potential of inner grid is decreased.
10) Once the -conduction starts, it can be stopped only by removing the anode potential.
11) The tube has capacity to flash 300 flashes per second.
12) The flashing light is directed on rotating member, which usually has some spoke, gear teeth or some other features.
13) If the rotating member does not have any of such features, a paper having black and white stripes, which is attached to it or some marking is done at a target.
14) The frequency of lamp flashing is adjusted until the target appears stationary.
15) Under this condition, speed is equal to flashing frequency.
16) If there are several marks on shaft, various errors in measurement arise.
17) If disc has m number of marks, then disc will appear stationary, The speed (n) = F ÷ m Where F = Number of flashes per sec. m = Number of marks on disc.
18) Single line image is obtained by flashes.
19) The flashing rate is gradually reduced and flashing frequencies are noted for all single line image.
20) If single line image are obtained at m different flashing rates, say F1, F2, … Fm. Then,
Speed of shaft (n) = Fm × F1 ( m – 1 ) ÷ ( Fm – F1 )
F1 = Lowest flashing frequency
Fm = Highest flashing frequency
m = Number of flashing points or frequency
21) Fig. 5. 5. 9 shows the stroboscope.
22) Following are few advantages and limitations of stroboscope.
Advantages of stroboscope :
1) It requires no special attachment with the shaft.
2) This method imposes no load on shaft.
3) It is very convenient to use a stroboscope for spot check on machinery speeds and for laboratory work.
4) This method is particularly useful where it is impossible to make contact with the shaft.
Limitations / Disadvantages of stroboscope :
1) Variable frequency of oscillator cannot be stabilized to give fixed frequency.
2) This method is less accurate therefore requires the use of digital meters.
3) Stroboscope cannot be used where surrounding light is above some level.
4) The stroboscope requires subdued lighting conditions for efficient operation.
In its simplest mechanical- type, a rotating cylinder (OR bowl with a raised edge) with equally spaced holes OR slots placed within the line of sight between the observer and also the moving object. The observer appearance through the holes/slots on the close to and much facet at an equivalent time, with the slots/holes occupancy opposite directions. once the holes/slots ar aligned on opposite sides, the article is visible to the observer.
Alternately, one moving hole or slot will be used with a fixed/stationary hole or slot. The stationary hole or slot limits light-weight|the sunshine} to one viewing path and reduces glare from light passing through alternative elements of the moving hole/slot.
Viewing through one line of holes/slots doesn’t work, since the holes/slots seem to simply sweep across the article while not a stroboscope impact.
The movement speed is adjusted so it becomes synchronized with the movement of the determined system, that appears to slow and stop. The illusion is caused by temporal aliasing, unremarkably referred to as the stroboscopic impact.