Optical Comparators

To adjust the optical comparator internal edge sensor so that it is exactly in the center of the screen cross lines use the following procedure.

Using only the optical comparator profile light, place an object on the optical comparator stage that will cast a straight image on the screen in a vertical and horizontal direction. A gage block would work fine. The image should cover all or at least half of the screen diameter.

Rotate the screen so the protractor is at zero. This will make the cross lines vertical and horizontal.

“Teach” the edge detector (refer to the optical comparator digital readout manual if necessary) and make sure that the readout beeps when you cross an edge. Note: You might have to move the image far from the center of the screen to test for the beep.

Bring the top of the image to the horizontal cross line. Making sure some of the image is left and right of the vertical cross line.

The adjustment for the optical comparator edge detector is located on the top of the comparator case. There are three button head screws in a triangle pattern approximately in the center on the case. Two screws on one side and one screw on the other. Turning either one of the screws on the side with two screws will move the location of the sensor up and down  (only a small amount of adjustment should be needed).

Adjust the up and down until the beep noise flutters. That indicates you are right on the line. Test the location by moving the image up and down. Re-adjust if necessary.

After the horizontal is adjusted align the right side of the image along the vertical cross line. Making sure some of the image is above and below the horizontal line. Adjust the left and right sensor using the single screw until the beep noise flutters. That indicates you are right on the line. Test the location by moving the image left and right. Re-adjust if necessary.

How internal edge detection works.

Light from the objective lens (main optical comparator lens) exits the back of the lens and passes through a “hot” mirror. This mirror reflects the infrared light and some visible light and lets most of the visible light pass through to form an image on the optical comparator screen. The light reflected by the hot mirror is directed up to a small mirror located inside the top of the comparator. From there it is directed down and onto a fiber optic cable located in the left front section of the optical comparator. In effect the fiber optic cable sees in infrared light anything that passes over the center cross lines of the screen. You will see the image on the screen in visible light.

As the edge of the part you are measuring passes over the cross lines located in the center of the screen the edge sensor (if turned on) will detect that the cross line area has moved from light to dark and will enter a point on the readout. Then as you continue moving the part the sensor will detect that the cross-hair area has changed from dark to light and enter another point.

By using internal edge detection you can speed up the inspection process and achieve greater accuracy of measured parts by eliminating some of the human error associated with lining up the part on the cross lines by eye.