What’s a Comparator?

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Dial gauges are used to measure machined parts with high accuracy, using plunger, lever, or vernier inputs. They come in analog or digital formats and can measure in small increments up to 500 thousand inches. Plunger gauges are held in place while the workpiece is rotated, while vernier gauges use the movement of the jaws. Digital gauges display measurements on an LCD screen. Care must be taken to maintain accuracy.

A dial gauge is a precision measurement commonly used to measure machined parts for manufacturing or wear tolerances. Comparators are capable of producing highly accurate measurement values; 0.00005 inch (0.001 mm) increments may be possible with some gauges. Measurement inputs are transferred to the gauge via a plunger, hinged lever, or the jaws of a vernier. Plunger tools are typically used in conjunction with a clamp or holder that holds the gauge in a fixed position relative to the workpiece. The piece is then rotated or moved to take measurements. Gauges are available with pointer and analog gauges or digital liquid crystal displays (LCD).

The dial gauge has long been a standard for engineers, craftsmen and do-it-yourselfers for making very precise measurements on precision parts. High levels of accuracy are possible in extremely small increments with typical measurement ranges ranging from 0.015 inch to 12 inch (0.25 – 300 mm) in increments up to 500 thousand inches (0.001 mm). There are two basic comparator formats; the first is the piston or lever calibre. Here, a spring-loaded plunger or lever at the bottom of the gauge transfers the height deviations of the workpiece surface to the gauge. The second type is the vernier dial gauge which receives its measurement input from the movement of the jaws of a conventional vernier scale.

Plunger type comparators are usually held in a fixed position while taking measurements. Specially designed magnetic or weighted clamps or holders are used to support the tool as the workpiece is rotated or moved. This process generally involves zeroing the gauge, adjusting its position until the plunger or lever rests on the workpiece, then rotating or moving the workpiece to check for abnormalities. The contact tip of a lever gauge is usually relatively small and fits narrow grooves where the plunger would not fit.

A vernier dial gauge uses the movement of the vernier jaws as a measurement input. These indicators indicate measurements on both the dial and the conventional vernier scale. The vernier caliper is capable of producing very accurate measurements across the measuring ranges of inside and outside diameter and the standard depth of the vernier. The analog comparator may be able to allow the needle to move around the dial multiple times if the measurement input is large enough. These gauges therefore have a smaller second dial, much like a wrist stopwatch, on the face that indicates the number of full revolutions of the needle.

Digital indicating comparators work in exactly the same way as their analog brethren, but display their measurements digitally on an LCD display. Many users find this gauge quicker and easier to read than the needle and dial type. As with all precision instruments, care should be taken to keep the dial gauge clean and not subject it to excessive shock to maintain accuracy.




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