A position sensor is a sensor that detects an object’s position. A position sensor may indicate the absolute position of the object (its location) or its relative position (displacement) in terms of linear travel, rotational angle or three-dimensional space. Different from the displacement sensor, the position sensor has two types: contact type and proximity type. The contacts of the contact sensor are moved by the contact and extrusion of two objects, and the common ones are the travel switch and the two-dimensional matrix position sensor. The travel switch has simple structure, reliable action and low price. When an object is in motion and encounters the travel switch, its internal contacts will act to complete the control. For example, if travel switches are installed at both ends of the X, Y, and Z axes of the machining center, the movement range can be controlled. The two-dimensional matrix position sensor is installed on the inside of the robotic palm to detect the contact position between itself and an object. Proximity switch refers to a switch that can send an “action” signal when an object is close to a set distance, and it does not need to be in direct contact with the object. There are many types of proximity switches, mainly electromagnetic type, photoelectric type, differential transformer type, eddy current type, capacitive type, reed switch, Hall type, etc. The applications of proximity switches on CNC machine tools are mainly tool rest tool selection control, table travel control, oil cylinder and cylinder piston travel control, etc. Also, there are potentiometer position sensor, Lvdt position sensor and so on.

Potentiometer, a common electromechanical component, is widely used in various electrical and electronic equipment. A potentiometer sensor is a sensor that converts mechanical displacement through a potentiometer into a resistance or voltage output that is a function of it. According to their different structural forms, they can be divided into wire-wound type, thin-film type and photoelectric type. According to the characteristics of input and output, it can be divided into linear potentiometer sensor and nonlinear potentiometer sensor. Most commonly used single-turn wire-wound potentiometers. Potentiometer-type resistance sensors are generally composed of resistance elements, skeletons and brushes. The movement of the brushes relative to the resistive element can be linear, rotational or helical. When the measured changes, the brush contacts move on the resistive element, and the resistance value between the contact and the resistive element will change, and the linear conversion between the displacement and the resistance can be realized. The resistive sensor is a kind of electrical parameter sensor that has been used earlier. It has a wide variety of applications and is widely used. After measuring the circuit, the changes being measured are reflected. The potentiometric sensor has a simple structure, good linearity and stability, and can form a force measurement, pressure measurement, weighing, displacement measurement, acceleration measurement, torque measurement, temperature measurement and other detection systems with the corresponding measurement circuit. It has become one of the indispensable means of production process detection and realization of production automation.

A linear scale, also called a bar scale, scale bar, graphic scale, or graphical scale, is a means of visually showing the scale of a map, nautical chart, engineering drawing, or architectural drawing. A scale bar is common element of map layouts. On large scale maps and charts, those covering a small area, and engineering and architectural drawings, the linear scale can be very simple, a line marked at intervals to show the distance on the earth or object which the distance on the scale represents. A person using the map can use a pair of dividers (or, less precisely, two fingers) to measure a distance by comparing it to the linear scale. The length of the line on the linear scale is equal to the distance represented on the earth multiplied by the map or chart’s scale. In most projections, scale varies with latitude, so on small scale maps, covering large areas and a wide range of latitudes, the linear scale must show the scale for the range of latitudes covered by the map. While linear scales are used on architectural and engineering drawings, particularly those that are drawn after the subject has been built, many such drawings do not have a linear scale and are marked “Do Not Scale Drawing” in recognition of the fact that paper size changes with environmental changes and only dimensions that are specifically shown on the drawing can be used reliably in precise manufacturing.

A thermometer is a device that measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer or the pyrometric sensor in an infrared thermometer) in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer or the digital readout on an infrared model). Thermometers are widely used in technology and industry to monitor processes, in meteorology, in medicine, and in scientific research. Thermometers utilize a range of physical effects to measure temperature. Temperature sensors are used in a wide variety of scientific and engineering applications, especially measurement systems. Temperature systems are primarily either electrical or mechanical, occasionally inseparable from the system which they control (as in the case of a mercury-in-glass thermometer). Thermometers are used in roadways in cold weather climates to help determine if icing conditions exist. Indoors, thermistors are used in climate control systems such as air conditioners, freezers, heaters, refrigerators, and water heaters. Galileo thermometers are used to measure indoor air temperature, due to their limited measurement range.

Pressure measurement is the analysis of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure in an integral unit are called pressure meters or pressure gauges or vacuum gauges. A manometer is a good example, as it uses the surface area and weight of a column of liquid to both measure and indicate pressure. Likewise, the widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge. A vacuum gauge is a pressure gauge used to measure pressures lower than the ambient atmospheric pressure, which is set as the zero point, in negative values (for instance, −15 psig or −760 mmHg equals total vacuum). Most gauges measure pressure relative to atmospheric pressure as the zero point, so this form of reading is simply referred to as “gauge pressure”. However, anything greater than total vacuum is technically a form of pressure. For very accurate readings, especially at very low pressures, a gauge that uses total vacuum as the zero point may be used, giving pressure readings in an absolute scale.

A pressure sensor is a device for pressure measurement of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the purposes of this article, such a signal is electrical. Pressure sensors are used for control and monitoring in thousands of everyday applications. Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, water level, and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters, pressure senders, pressure indicators, piezometers and manometers, among other names.
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