A spherometer is a mechanical engineering device that accurately measures the radius of a curved surface. It consists of a three-legged base with a screw and measuring dial, and can be used to measure the thickness of thin or flat sheets. Digital versions are available but may sacrifice accuracy.
A spherometer is a device used in mechanical engineering to obtain the precise measurement of the radius of a circle. It is a unique measuring tool as it can accurately measure curved surfaces. The instrument was originally designed to give opticians the ability to measure the curvature of glass lenses without having to rely on expensive interferometry equipment.
Most spherometers consist of a three-legged base that takes the shape of an equilateral triangle. All legs taper to thin points at the bottom. In the center of the base is a screw with a fine point that is attached to a nut and a measuring dial. There is usually a vertical scale attached to the side of the spherometer, which is used to indicate how many full turns of the nut have been made, as well as to provide an index to read the fine measurement dial attached to the screw.
To get a reading from a spherometer, the instrument must be completely level. Then it can be placed on the object to be tested. All four fine points must exert the same amount of pressure before the measurement can be read. The difference between the measurements shows the thickness of that area, which is cut by a plane passing through the three equidistant feet. Using r to indicate the overall distance and s for the distance between the feet, the radius can be determined using the formula R=r2+s2/2s.
There are also digital spherometers, which usually come in two forms. The first form allows users to get a measurement right on the device: instead of a measurement dial, the screw will have a plate with a digital face. The second form involves a spherometer without a face readout, which instead connects to a separate device that prints a digital readout. A digital spherometer device may be easier for users to read, but there is some concern that it comes at a cost to accuracy. A digital unit may not be able to record the roughness on a surface like a standard dial spherometer can.
While spherometers are still commonly used by opticians, they can also be found in other fields, usually as quality control devices. For example, a spherometer might be useful for testing drill rods before shipping them to companies to make sure they don’t break in use. It can also be used by anyone who needs to measure the thickness of thin or flat sheets.
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