Author: Haroon Khalil

A hot wire anemometer involves the heat that is dissipated by a hot wire to an ambient fluid passing through it. For a fixed wire temperature, the heat dissipation from the wire will be larger with larger velocity of the fluid. Alternately, for a fixed heat dissipation rate from the wire, the wire temperature will…

The arrangement for measuring fluid velocity using a Pitot tube is shown in Figure 18.5. The Pitot tube consists of bent tube of small diameter with a rounded nose. The Pitot tube is connected to one limb of a U tube manometer. The other limb of the manometer is connected to a tap made on the tube…

When operating below the Pirani gauge range, an ion gauge can be used to measure pressure. The ion gauge consists of three distinct parts: the filament, the grid, and the collector. The filament produces electrons by thermionic emission. A positive charge on the grid attracts the electrons away from the filament; they circulate around the grid…

The Pirani gauge is a roughing pressure vacuum gauge. It uses the thermal conductivity of gases to measure pressure. The Pirani gauge head is based around a heated wire placed in a vacuum system, the electrical resistance of the wire being proportional to its temperature. At atmospheric pressure, gas molecules collide with the wire and…

The Bourdon tube pressure gauge, named after Eugène Bourdon, is a very popular pressure sensor. Basic Bourdon tubes are made from metal alloys such as stainless steel or brass. They consist of a tube of elliptical or oval cross-section, sealed at one end. There are various shapes of Bourdon tube, including helical, spiral, and twisted.…

Manometers are differential pressure sensors. A differential pressure sensor measures the difference between a pressure being applied to it and a reference pressure (often atmospheric pressure). The U-tube manometer consists of a clear glass or plastic tube shaped into the form of a ‘U’. The tube is partially filled with a liquid, such as water,…

Pressure is force per unit area on a surface. There are some relative terms such as gauge pressure, atmospheric pressure, and absolute pressure those can be understood easily with Figure 18.2. Figure 18.2 Relative Terms of Pressure Gauge Pressure: It is the pressure relative to atmospheric pressure. Gauge pressure is positive for pressures above atmospheric pressure and negative…

Change-of-state temperature sensors consist of labels, pellets, crayons, lacquers, or liquid crystals whose appearance changes once a certain temperature is reached. They are used, for instance, with steam traps—when a trap exceeds a certain temperature, a white dot on a sensor label attached to the trap will turn black. Response time typically takes minutes, so…