Laser stands for “Light Amplification by Stimulated Emission of Radiation”. Laser instruments are devices to produce powerful, monochromatic collimated beam of light in which the waves are coherent.
The development of laser gives production of clear coherent light. The biggest advantage of this coherent light is that whole energy appears to be emanating from a very small point.
The laser beam can be focused easily into either a parallel beam or into a very small point by the use of lens.
A typical helium neon laser source produces a 1 to 2mm diameter beam of pure red light having power of 1MW. So, this type of a beam is focused at a point. It means, beam has very high intensity.
The laser is used extensively for interferometry. Upto a great distance beam has no divergence but ther. it begins to expand at a rate of about 1 mm/m.
The laser beam is visible and it can be observed easily. Its centre can be easily judged to an accuracy of 1mm over 2m. This is used for very accurate measurements in the order of 0.1 um in 100m.
Laser Metrology
A laser beam projected directly onto a position detector is a method of alignment used in a number of commercially available systems. The laser with its highly controlled frequency modes and coherent output are used extensively for interferometry (He – Ne gas type).
Laser is suitable for more general applications where a very convenient, collimated and high intensity source is required. (Precision, accuracy, no contact and hot moving parts)
Laser diodes, semiconductor lasers have more advantages at lower cost. Laser instruments are very much suitable in surface inspection and dimensional measurements.
Laser Telemetric System
Laser telemetric system is a non contact gauge that measures with a collimated laser beam. It measures at the rate of 150 scans per second.
Construction:
The laser telemetric system consists of mainly three components, namely
The transmitter produces a collimated parallel scanning laser beam moving at a high constant linear speed. The beam appears as red line after scanning.
The receiver collects the laser beam and photo electrically senses the laser light transmitted through the object being measured. The processor receives the signal and converts it into convenient form.
The transmitter has the following components.
- Low power helium neon gas laser.
- Synchronous motor.
- Collimating lens.
- Reflector prism.
- Synchronous pulse photo detector.
- Replaceable window.
Working:
The object to be measured is placed in the measurement region. High constant and linear speed laser beams form transmitter which is focused on the object to be measured. The receiver module collects and senses the laser light transmitted past the object to be measured.
After sensing, the processor electronics take the received signals and convert them into a convenient form and then display the dimensions being gauged.
Advantages:
- It is possible to detect changes in dimensions when components are moving.
- It is possible to detect changes in dimensions when product is in continuous processes.
- There is no need to wait for taking measurements when the product is in hot conditions.
- It can be applied on production machines and controlled them with closed feedback loops.
- It is possible to write programs for the microprocessor to take care of smoke, dust and other airborne interference around the work piece being measured.
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