What is Optical Comparator (Profile Projector )| Instrumentation

What is Optical Comparator (Profile Projector )| Instrumentation
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In today’s post, we will learn about what actually an optical comparator is and how important it is for calibrations of a large number of instruments in Metrology. Optical Comparator is also known as a profile projector  . W will discuss in detail in our next post regarding the procedure to use Profile Projector, list of instruments that are used for calibration using this device.

Optical Comparator

This measuring device makes use of principles of optics for the inspection of manufactured parts. For the precise measurement of manufactured parts such as

1.) Measuring wire thickness and distance between wires in Sieves

2.) Calibration of Radius Gage leaves

and lot more.


In a Profile Projector, the technician projects the magnified silhouette of a part upon the screen by focussing the part in front of the lens below the big screen as shown above. The dimensions and geometry of the part are measured against prescribed limits and can be read from the display screen on the right side of the instrument. Display screen gives value both in Inches and Millimeters as some industries take imperial values while others take metric. This measuring instrument is widely used in a small parts machine shop or production line for precise measurements so as to maintain the product quality and operational effectiveness.

Download Temperature Measuring Instruments PowerPoint Presentation 

Application of Optical Comparator

Below is the list of areas where this calibration device is used to calibrate and to do the measurement of the instruments. Major industries include aviation, watches, aerospace industry,  electronics, and various research institutes

Optical Comparator is a great relief in the measurement of complex shapes of instruments such as

  • Complex shape stampings
  • Small-sized gears and cams
  • Complex and small threads
  • To compare the measured contour model.
  • Biomedical instruments

Work principle for Profile Projector

Let us discuss the working principle of this measuring device. It is quite easy to use this device but only thing that one should keep in mind that they need to pay extra attention while taking readings from the display screen and always try to keep the object well focussed.

Keep the specimen in front of the lens ( Depending upon the requirement 20X or 50X magnification lens is used ). The device magnifies the profile of the specimen and displays this on the built-in projection screen. The screen where it is projected is actually a grid that can be rotated 360 degrees so that just in case we need to align the X-Y axis of the screen with a straight edge of the machined part, it can be done so as to make the measurements easy. The magnified image is displayed on the screen and one can take the required measurements.


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