Compensated Leg Systems The simple and direct relationship between liquid height in a vessel and pressure at the bottom of that vessel is ruined if another source of pressure exists inside the vessel other than hydrostatic (elevation head). This is virtually guaranteed to be the case if the vessel in question is unvented. Any gas […]
Hydrostatic Interface Level Measurement Hydrostatic pressure sensors may be used to detect the level of a liquid-liquid interface, if and only if the total height of liquid never drops down into the sensing range of the interface level instrument. This is critically important because any single hydrostatic-based level instrument cannot discriminate between a changing interface
Mechanical Pressure Sensing Elements Mechanical pressure-sensing elements include the bellows, the diaphragm, and the bourdon tube. Each of these devices converts a fluid pressure into a force. If unrestrained, the natural elastic properties of the element will produce a motion proportional to the applied pressure. Bellows resemble an accordion constructed from metal instead of fabric.
Manometer Construction and Working A very simple device used to measure pressure is the manometer : a fluid-filled tube where an applied gas pressure causes the fluid height to shift proportionately. This is why pressure is often measured in units of liquid height (e.g. inches of water, inches of mercury). As you can see, a
Different Types of Process Control Switches There are different types of process control switches. These are: Limit Switch A limit switch detects the physical motion of an object by direct contact with that object. An example of a limit switch is the switch detecting the open position of an automobile door, automatically energizing the cabin
Construction, Working & Types of Synchros and Resolver It is a general name for self-synchronizing machines which, when electrically energized and electrically interconnected, exert torques which cause two mechanically independent shafts either to run in synchronism or to make the rotor of one unit follow the rotor position of the other. They are also known
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Analog to Digital Conversion Physical quantities like temperature, pressure, velocity etc. can be measured using transducer circuits. The resulting analog voltage produced by a transducer is often converted to digital form so that it can be processed by a computer or a digital signal processor (DSP). The conversion of an analog signal to digital utilizes
Method of Measuring Displacement, Velocity and Acceleration Displacement is a quantity that indicates the change in position of a body or point. Angular displacement refers to a rotation that can be measured in degrees or radians. Displacement transducers can be either contacting or noncontacting. Contacting transducers typically use a sensing shaft with a coupling device
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Method of Measuring Strain, Pressure, and Flow Rate Strain is the deformation, either expansion or compression, of a material due to a force acting on it. For example, a metal rod or bar will lengthen slightly when an appropriate force is applied, as illustrated in Figure 1(a). Also, if a metal plate is bent, there
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Methods of Measuring Temperature Temperature is the most common physical parameter that is measured and converted to electrical form. Several types of temperature transducers respond to temperature and produce a corresponding indication by a change or alteration in a physical characteristic that can be detected by an electronic circuit. Common types of temperature transducers are