Gauge (instrument)

This article is about gauges (gages) in engineering. For other uses, see Gauge (disambiguation). For the other spelling, see Gage (disambiguation).

In engineering, a gauge or gage, is used to make measurements. A wide variety of tools exist which serve such functions, ranging from simple pieces of material against which sizes can be measured to complex pieces of machinery. Various types of gauges include:

A bore gauge, a device used for measuring holes. A caliper, a device used to measure the distance between two opposing sides of an object. Center gauges and fishtail gauges are engineering gauges used in lathe work for checking the angles when grinding the profiles of single-point screw-cutting tool bits and centers. A dial indicator, also known as a dial test indicator, dial gauge, or probe indicator, is an instrument used to accurately measure small linear distances. A feeler gauge is a simple tool used to measure gap widths. A gauge block, (also known as a gage block, Johansson gauge, slip gauge, or Jo block) is a precision ground and lapped length measuring standard. It is used as a reference for the setting of measuring equipment used in machine shops, such as micrometers, sine bars, calipers, and dial indicators (when used in an inspection role). A gauge pin is similar to a gauge block. It is a precision ground cylindrical bar for use in Go/no go gauges or similar applications. A Go/no go gauge is an inspection tool used to check a workpiece against its allowed tolerances. Its name derives from its use: the gauge has two tests; the check involves the workpiece having to pass one test (Go) and fail the other (No Go). A load cell is a transducer that is used to convert a force into electrical signal. This conversion is indirect and happens in two stages. Through a mechanical arrangement, the force being sensed deforms a strain gauge. The strain gauge converts the deformation (strain) to electrical signals. A load cell usually consists of four strain gauges in a Wheatstone bridge configuration. Load cells of one strain gauge (quarter bridge) or two strain gauges (half bridge) are also available. The electrical signal output is typically in the order of a few millivolts and requires amplification by an instrumentation amplifier before it can be used. The output of the transducer is plugged into an algorithm to calculate the force applied to the transducer. The linear variable differential transformer (LVDT) is a type of electrical transformer used for measuring linear displacement. The transformer has three solenoidal coils placed end-to-end around a tube. The center coil is the primary, and the two outer coils are the secondaries. A cylindrical ferromagnetic core, attached to the object whose position is to be measured, slides along the axis of the tube.

A micrometer, sometimes known as a "micrometer screw gauge", is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier, and digital calipers. Micrometers are often, but not always, in the form of calipers. A pressure gauge or vacuum gauge is used for pressure measurement. A profile gauge or contour gauge is a tool for recording the cross-sectional shape of a surface. A radius gauge, also known as a fillet gauge, is a tool used to measure the radius of an object. Radius gauges require a bright light behind the object to be measured. The gauge is placed against the edge to be checked and any light leakage between the blade and edge indicates a mismatch that requires correction. A ring gauge is a cylindrical ring of steel whose inside diameter is finished to gauge tolerance and is used for checking the external diameter of a cylindrical object. Strain gauge is a device used to measure the strain of an object. A stream gauge is a site along a stream where measurements of water surface elevation ("stage") and/or volumetric discharge (flow) are made. A thermometer or temperature gauge is a device that measures temperature or temperature gradient using a variety of different principles. A thread pitch gauge, also called a threading gauge, pitch gauge, or screw gauge, is used to measure the pitch or lead of screw threads. A tide gauge is a device for measuring sea level and detecting tsunamis. Vernier height gauge is a measuring device used either for determining the height of something, or for repetitious marking of items to be worked on. The former type of height gauge is often used in doctor's surgeries to find the height of people. A wire gauge measuring tool determines the thickness of a wire.