Capacitive sensor

The Series 1151 differential pressure transmitter manufactured by Rosemount (MinneapoHs, Minnesota) uses a capacitance sensor in which capacitor plates are located on both sides of a stretched metal-sensing diaphragm. This diaphragm is displaced by an amount proportional to the differential process pressure, and the differential capacitance between the sensing diaphragm and the capacitor plates is converted electronically to a 4—20 m A d-c output. 

Fig. 16. Exploded view of a smart transmitter based on variable capacitance sensor technology.

Capacitive sensors are small and rapidly respond to changes in air humidity. The measurement range is 0-100% RH. Due to the electrical principle, they can... 

Capacitive Sensors. This device usually consists of a capacitor which is formed either from two concentric cylinders or from a pair of parallel plates. The solid sample to be analyzed for moisture content is passed between these plates. Since w has a large dielectric constant, the w content of the sample causes a significant change in the dielectric constant of the solid, which is measured using bridge or frequency techniques. 

Mortari, A., Maaroof A., Martin, D. and Cortie, M.B. (2007) Mesoporous gold electrodes for measurement of electrolytic double layer capacitance. Sensors and Actuators B, 123, 262-268. 

Push button Capacitive sensors Touch sensitive switches P... 

Gopel, W. Schierbaum, K.D. Electronic Conductance and Capacitance Sensors. In Sensors A comprehensive Survey. 

With the Ee301 EDISEN - electronic GmbH extent the application possibilities of it s digital capacitive sensors. 

Fence-associated sensors. Fence-associated sensors are either attached to an existing fence, or are installed in such a way as to create a fence. These sensors detect disturbances to the fence—such as those caused by an intruder attempting to climb the fence, or by an intruder attempting to cut or lift the fence fabric. Exterior fence-associated sensors include fence-disturbance sensors, taut-wire sensor fences, and electric field or capacitance sensors. Details on each of these sensor types are provided below. 

Microhotplates, however, are not only used for metal-oxide-based gas sensor applications. In all cases, in which elevated temperatures are required, or thermal decoupling from the bulk substrate is necessary, microhotplate-like structures can be used with various materials and detector configurations [25]. Examples include polymer-based capacitive sensors [26], pellistors [27-29], GasFETs [30,31], sensors based on changes in thermal conductivity [32], or devices that rely on metal films [33,34]. Only microhotplates for chemoresistive metal-oxide materials will be further detailed here. The relevant design considerations will be addressed. 

The features of the monoHthic integrated sensor systems have not yet been fully exploited. The almost linear relationship between input reference voltage and microhotplate temperature renders the systems suitable for applying any temperature modulation protocol. Due their compatibility with other CMOS-based chemical sensors the microhotplates can be also combined with, e.g., polymer-based mass sensitive, calorimetric or capacitive sensors. The co-integration with such sensors can help to alleviate problems resulting from cross-sensitivities of tin-oxide based sensors to, e.g., volatile compounds such as hydrocarbons. A well-known problem is the crosssensitivity of tin oxide to humidity or ethanol. The co-integration of a capacitive sensor, which does not show any sensitivity to CO, could help to independently assess humidity changes. 

A typical capacitive sensor is illustrated diagrammatically in Fig. 6.11. The element consists of a gas filled parallel plate capacitor in which one plate is a flat circular diaphragm whilst the other is a fixed metal disc. When the pressure on the outside surface of the flexible diaphragm is increased by an amount SP compared with the pressure within the unit, the diaphragm is deflected by an amount w at a radius r, (assuming the distorted section to be smoothly curved) given by (Volume 6, Section 13.3.5) ... 

W. Bracke, P. Merken, R. Puers and C. Hoof, On the optimization of ultra low power front-end interfaces for capacitive sensors, Sens. Actuators A Phys., 117(2) (2005) 273-285. 

P. Temple-Boyer, J. Launay, G. Sarrabayrouse and A. Martinez, Amplifying structure for the development of field-effect capacitive sensors, Sens. Actuators B Chem., 86(2-3) (2002) 111-121. 

The resolution of a capacitive sensor is determined by the changes in capacity that can still be measured. With the sensor dimensions used by M KS Instruments, a minimum deflection of y = 10 10/m can be measured, resulting in a low measurable pressure of-1.10-6 mbar. 

In this work, we develop an electrical capacitance sensor that consists of only two electrodes placed around a glass tube. This set up is considered not in the view of imaging... 

It is also interesting to briefly consider online measurements of variables different from temperature [5], Since pressure is defined as the normal force per unit area exerted by a fluid on a surface, the relevant measurements are usually based on the effects deriving from deformation of a proper device. The most common pressure sensors are piezoresistive sensors or strain gages, which exploit the change in electric resistance of a stressed material, and the capacitive sensors, which exploit the deformation of an element of a capacitor. Both these sensors can guarantee an accuracy better than 0.1 percent of the full scale, even if strain gages are temperature sensitive. 

An ECT system is composed of three basic components (1) a capacitance sensor, (2) a data acquisition system, and (3) a computer system for reconstruction and viewing. Figure 1 is a sketch of the ECT system with all three components (Warsito and Fan, 2003). The capacitance sensor is made of nr capacitance electrodes distributed around the wall of the process vessel. The ne capacitance electrodes provide up to ne(ne—1)/2 combinations of independent capacitance measurements between the electrode pairs. The capacitance measurements are related to the local dielectric constant (permittivity) filling the process vessel between electrode pairs (Figure 2) (Warsito and Fan, 2001b). The relation between the electric potential and the permittivity distributions follows Poisson equation shown in Equation (1). 

A direct comparison of some representative sensors to estimate biomass in bacterial and yeast cultures was made by Nipkow et al. [309], by Fehrenbach et al. [107], by Konstantinov et al. [219] and, more recently, by Wu et al. [465]. These studies are of importance because the sensors were mounted in situ and used in parallel. Most of the sensors measured the optical density (OD), one the autofluorescence of the cultures (fluorosensor) and another was a capacitance sensor (Cugmeter). 

Acetylcholine receptor from electric organ of Torpedo sp. Receptor protein noncovalently bound on the surface of a planar interdigitated capacitative sensor. Response was concentration dependent and specific for ACh and inhibited by (+ )-tubocurarine, amantidine and a-neurotoxin. [66]... 

Another alternative to using multiple beam interferomtery for surface separation determination was offered by Stewart [76] who coupled a capacitance sensor to the SFA Mark IV to measure the deflection of the double cantilever force measuring spring. The capacitance dilatometry method enables the study of opaque surfaces at the same time as the distance and force normalised to the radius resolution remain equal to that of the regular SFA, or even better [77], However, using this method, the absolute separation cannot be determined. 

A capacitance sensor [351], in general based on the resonance-peak-shift principle, is connected to the conductive SFM tip. 

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