Capacitive pressure

Fig. 11. Capacitive pressure sensor in the differential measurement configuration. Courtesy of Rosemount, Inc.

Fig. 5.61 shows a section through a capacitive pressure sensor. It consists of a metallic housing that is divided into two chambers by the electrically conductive... 

Capacitance manometers, 20 658-659 Capacitance probes, 20 681 Capacitive pressure transducers, 20 656-657... 

Fig. 6.11. Capacitive pressure sensor with flexible diaphragm...

Capacitive pressure transducers are traditionally used for relatively low pressure ranges (up to about 800 kPa) and for vacuum measurement (Section 6.3.5). 

A classical volumetric adsorption apparatus equipped with absolute capacitance pressures transducers can be used for the estimation of adsorption isotherms in the pressure range 10-3 mbaradsorption measurements the carbon black samples are extracted with toluene and water/methanol (1 1) and after drying degassed overnight at 200 °C at a pressure below 10 4 mbar. The time allowed for equilibrium of each point of the isotherm is 5-90 min depending on the sample and the adsorbed amount. 

Simple gas adsorption manometry. A simple modem set-up with three valves and a capacitance pressure transducer is shown in Figure 3.2. The dosing volume is within the central cross, i.e. in the connecting tubes between the valves and the pressure transducer. 

Nowadays, membrane capacitance pressure transducers are the most widely used manometers for adsorption studies. A single pressure transducer can be chosen to cover a wide pressure range, but since they lose part of their performances over the lowest few percent of the range, it is usually advisable to have two (e.g. 0-10 and... 

Fung C D and Ko W H 1982 Miniature capacitive pressure transducers Sensors... 

The model for a variable capacitance pressure transducer was developed in Appendix 11A and is given by eq. (13.9). It shows that the system is inherently second-order and can exhibit underdamped response. What does this mean for the applicability of such device ... 

Other more rehned methods that rely on pressure difference include the combination of different types of pressure probes, e.g. a combination of a capacitance pressure probe and a Pirani gauge. The former device measures the total pressure, whereas the Pirani reading is affected by the thermal conductivity of the gas, e.g. water vapour. Completion of sublimation is indicated when both pressure readings coincide. 

Eor tubular membranes, the permeation flux measurements are generally carried out by a shell-and-tube arrangement as shown in Fig. 13.2 [7]. Since the membrane is plated on the outside of the porous substrate, the feed gas flows upward through the outside of the membrane (shell side), and the permeate gas is collected on the tube side. A purge gas can also be used on the tube side if desired. The upstream pressure is monitored by a capacitance pressure transducer and the permeate side pressure is kept atmospheric. The gas permeation rate (the volumetric flow rate) is measured in the permeate side at atmospheric pressure and room temperature. For mixture experiments, the permeate and retentate can be analyzed by an online gas chromatograph equipped with appropriate detectors, such as Thermal Conductivity Detector (TCD), Flame Ionization Detector (FID) or others, depending on the specific gas mixture... 

Kirstein, T., Meyer, U., Troster, G., (ETH Zurich), 2005. Textile Capacitive Pressure Sensor. World patent iqrpUcation PCT WO 2005/121729. 

Sergio, M., Manaresi, N., Tartagni, M., Guerrieri, R., Canegallo, R., 2002. A textile based capacitive pressure sensor. Proceedings of IEEE 2, 1625—1630. 

Chang SP, Allen MG (2004) Demonstrahon for integrating capacitive pressure sensors with read-out circuitry on stainless steel substrate. Sensors and Actuators A. 116 195-204. 

A capacitance probe was developed in our work (Brereton and Grace, 1992) based upon a DISA capacitative pressure transducer system. It effectively measures the instantaneous suspension density in an approximately 5 mm cubic zone surrounding the exposed needle. The capacitance probe was used to study radial variations and the form of solids flow structures present in the developing region of a cold circulating bed. Sand particles with a mean diameter... 

Example 8.3. If a diaphragm is used in a capacitance pressure transducer, it must not have a natural frequency or an appreciable harmonic in the range of pressure oscillations likely to be encountered. To avoid this occurrence, the following equation is used to calculate the natural frequency, N, of a circular diaphragm ... 

In capacitive pressure transmitters, the primary element is a membrane that has metal in its irmer part, and that is a central plate of a two capacitor system. As the membrane displaces to one side, it increases the capacitance of one capacitor, and decreases the capacitance of the other, therefore, the capacitance of the system changes. There is a linear relationship between the capacitance and the displacement. 

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