Differential pressure signal

Gourich B, Vial C, Essadki AH, AUam F, Soulami MB, Ziyad M. (2006) Identification of flow regimes and transition points in a bubble column through analysis of differential pressure signal— influence of the coalescence behavior of the hquid phase. Chem. Eng. Process., 45 214—223. 

As shown, there is quite a bit of scatter in the data. These differential pressure signals are less than 0.25% of the ullage pressme, therefore small fluctuations in tank pressure can cause large fluctuations in the pressure taps inside the channel, and thus the measmed frictional pressure drops. Nonetheless, a smooth curve is fit to the data to compare directly with the model. 

Figure 7-16 indicates several key control loops (a) The pressure of the core system is controlled from sensed pressure by the proportioning of power to the pressurizer electric heaters the blanket pressure is similarly controlled by a core-to-blanket differential-pressure signal. (b) The liquid levels in the pressurizers are controlled from sensed levels by pneumatic control of the letdown valves. Pneumatic control actions are derived from transducers which receive signals from electric transmitters. Electric interlock control of the pneumatic signals to final control elements is achieved by the use of solenoid-actuated pilot valves. 

Flow meters have traditionally been classified as either electrical or mechanical depending on the nature of the output signal, power requirements, or both. However, improvement in electrical transducer technology has blurred the distinction between these categories. Many flow meters previously classified as mechanical are now used with electrical transducers. Some common examples are the electrical shaft encoders on positive displacement meters, the electrical (strain) sensing of differential pressure, and the ultrasonic sensing of weir or flume levels. 

The pressure limiting eontroller prevents the absolute diseharge pressure from the regenerator from exeeeding an upper threshold. The aetion signal from this eontroller overrides the aetion of the differential pressure eontroller. 

The flow transmitter (transducer block) senses the flow element differential pressure, converts this signal to a signal proportional to the process flow, and sends it to the flow controller. 

Pressure signal transmission—the differential pressure cell... 

Pressure measurements are made with four differential pressure transducers which produce a 0- to 5-VDC output signal from an unregulated 24-VDC Input. The range of three of the transducers 1s 0 to 500 psi and the other 1s 0 to 320 psl. The signal from these transducers 1s connected to an analog Input card 1n the HP 3497. 

Tumble dryers use pressure sensors for filter measurements by measuring the differential pressure across the lint filter signalling the user when to clean the filter. 

If orifice plates are used as flow sensors, the signals from the differential-pressure transmitters are reaUy the squares of the flow rates. Some instrument engineers prefer to put in square-root extractors and convert everything to linear flow signals. 

Acoustic emission from fluid flow through an orifice plate inserted in a pipeline contains a wealth of information, which can be used to predict, for example composition, flow or density [5]. Acoustic signatures from fluid flow are affected by several physical factors such as flow rate differential pressure over the orifice plate static pressure as well as chemical-physical factors - density, composition, viscosity. It is the objective of PLS modeling to extract the relevant features from the acoustic spectra and make use of these embedded signals in indirect multivariate calibration [1,2]. Several successful examples, including prediction of trace concentrations of oil in water, have been reported [5]. 

FIGURE 3.18 Response to selected detectors as a function of retention volume for myoglobin (dissolved in PBS buffer at a pH of 6.9). The three detectors are the RI = refractive index signal, LS = lightscattering signal, and DP = differential pressure transducer (viscosity signal). (Courtesy of Viscotek, Houston, TX. With permission.)... 

The use of a multiventuri system (in which an inner venturi discharges into the throat of an outer venturi) to increase both the differential pressure for a given flow rate and the signal-to-loss ratio is described by Klomp ana Sovran [/. Basic Eng., 94, 39 5 (1972)]. 

Pressure is measured extensively in the chemical processing industries and a wide variety of pressure measuring methods has been developed. Some of these have already been discussed in Volume 1, Section 6.2.2, viz. the manometer (which is an example of a gravity-balance type of meter), the Bourdon gauge (an example of an elastic transducer) and mention is made of the common first element in most pressure signal transmission systems—the differential pressure (DP) cell (Volume 1, Section 6.2.3). The latter also frequently forms part of a pneumatic transmission system and further discussion of this can be found in Section 6.3.4. 

Differential pressure transmitters (or DP cells) are widely used in conjunction with any sensor that produces a measurement in the form of a pressure differential (e.g. orifice plate, venturi meter, flow nozzle, etc.). This pressure differential is converted by the DP cell into a signal suitable for transmission to a local controller and/or to the control room. DP cells are often required to sense small differences between large pressures and to interface with difficult process fluids. Devices are available that provide pneumatic, electrical or mechanical outputs. 

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