Capacitance probes

Capacitance probes can detect the levels of both conductive and nonconduc-tive liquids, liquid-liquid interfaces, and levels of solids. Their measurement error is about 1% FS, and their temperature and pressure ratings are up to 1,100°C (2,000°F) and 1,400 bar (20,000 psig). 

RF probes operate by applying a constant voltage to a metallic rod and monitoring the current, which is proportional to the admittance or capacitance (if conductivity is absent). The current then flows to a second electrode, such as the tank wall. The difference between conductance and RF probes is that the conductance types use DC or low-frequency AC, whereas the latter 

Post-Oil Energy Technology After the Age of Fossil Fuels 

Capacitance probes can be used with flowing suspensions as well as in fluidized beds to evaluate voidage and particle concentration through Equations 3.14 and 3.15 together with the relationship between voidage, particle volume, and concentration given by 

FIGURE 3-17 Capacitance probes needle-type (left) plate-type (right). 

With two capacitance probes positioned at a known separation distance (as in a fluidized bed), the velocity of the solids phase interface can be determined by measurement of a disturbance such as a bubble. Small probes can be designed to be used within the system or mounted flush with the walls and may include a 

A simple example of an ideal parallel plate capacitor will demonstrate the capacitance method. A capacitance probe driven by an ac source can detect a disturbance signal from any one of the fundamental parameters , A, x as illustrated by the equation for a parallel plate capacitor 

For subsequent demodulation and a good signal profile recovery, the period of the ac carrier frequency T = 1/f = 2k/(0 should be small compared to the duration of the signal (i.e., less than 1 s), the ratio being 1 10 in this example. 

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A Btu meter may be used in the fuel-quality system as an aid in determining turbine system efficiency. A water capacitance probe is used for detection of water in the fuel line. A water-detecting device can be incorporated into the corrosion monitoring system. This monitoring device is based on detection of changes in the dielectric constant of unknown fluid components... 

Capacitance Probe 2.2.5 Computational Modules- 3.5.3.3 Valves-Operated-Pneumatic... 

Taxonomy No. 2.1.3.1.2.3 Equipment Description TRANSMITTERS-ELECTRONIC LEVEL- CAPACITANCE PROBE ... 

Capacitance probes A capacitometer, used as a transducer, measures the gap capacitance between a plate whose area is small compared to the wave and a grounded conducting surface across which the liquid film flows (Nakanishi et al., 1979). 

Almstedt, A. E., and Zakkay, V., An Investigation of Fluidized-bed Scaling-capacitance Probe Measurements in a Pressurized Fluidized-bed Combustor and a Cold Model Bed, Chem. Eng. Sci., 45(4) 1071 (1990)... 

It was experimentally confirmed, using capacitance probes, that the solids flow down the downcomer at close to minimum fluidization, thus ebd = 0. 

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

Fig. 13. Schematic of a wafer shape measured using a noncontact capacitance probe. The warp and bow are exaggerated. (Courtesy of ADE Corporation, Westwood, MA.)...

Figure 20.1 Capacitance probe high-pressure cavity and seals for continuous intrusion-extrusion measurements. 

The mercury level is monitored with a capacitance probe as shown in Fig. 20.1. The signal from the capacitance probe and from the pressure transducer are plotted on an X-Y recorder as intrusion volume and pore radius, respectively. 

The cantilever bending-technique requires a sensitive displacement detection such as a capacitance probe (Klokholm 1976, 1977), optical interferometry (Sontag and Tam 1986), a tunnelling tip (Wandass et al. 1988) or angular detection (e.g. laser beam deflection, Son-tag and Tam 1986 Trippel 1977 Tam and Schroeder 1988 Betz 1997 Sander et al. 1998). 

If the material is non-conducting then a bare capacitance probe can be employed—otherwise the probe must be insulated. Difficulties can arise due to unexpected variations in the dielectric constant of the material being measured (e.g. in the case of a powder which is prone to absorb water vapour). 

The choice of a filler depends on the number of bottle sizes being considered for use on it. For example, if 3 1 PET bottles are to be filled, a 126 mm pitch between filling valves is required. If only small bottles up to 500 ml are to be filled, then a 70 mm pitch will suffice. This has a direct effect on the size of the filler and its footprint on the factory floor. Unless the filler bowl level is kept within tightly controlled limits, pressure head variations will affect the rate of flow into containers. Systems such as that shown in Figure 7.15 need to be employed. Wherever possible there should be minimal contact between any instrumentation and the product. Conventional float valves should be avoided and simple capacitance probes, which are easily cleanable but small and very effective, should be used. It is not uncommon in older fillers to only have one float valve. This often gives rise to filler bowl flooding, which may lead to inconsistent fill level and poor counter-pressurisation of the container pre-filling. 

E. Brunazzi, A. Paglianti, S. Pintus, A capacitance probe and a new model to identify and predict the capacity of columns equipped with structured packings, Ind. Eng. Chem. Res. 40 (2001) 1205—1212. 

Laser Coriolis Optical fiber Laser Capacitance probe... 

Thermal Mass Flowmeters The trend in the chemical process industries is toward increased usage of mass flowmeters that are independent of changes in pressure, temperature, viscosity, and density. Thermal mass meters are widely used in semiconductor manufacturing and in bioprocessing for control of low flow rates (called mass flow controllers, or MFCs). MFCs measure the heat loss from a heated element, which varies with flow rate, with an accuracy of 1 percent. Capacitance probes measure the dielectric constant of the fluid and are useful for flow measurements of slurries and other two-phase flows. 

Capacitance probe, conductivity cell, float gauge,... 

In measurement and visualization of gas-solid flow in fast fluidization, various techniques have been developed and used, such as pressure gradient, pressure fluctuation, capacitance probe, optical fiber probe, momentum probe, laser Doppler velocimeter, night-television, and video camera. The resulting data on local gas and solid velocity, solids concentration and its... 

The nature of the tracer dictates the detection system. For the liquid phase, quite often the tracers (e.g., NaCl, H2S04, etc.) are such that the detection probe is directly inserted into the reactor and continuous monitoring of the concentration at any fixed position is obtained by means of an electrical conductivity cell and a recorder. In this case, no external sampling of liquid is necessary. If the tracer concentration measurement requires an analytical procedure such as titration, etc., sampling of the liquid is required. For the solid phase, a magnetic tracer is sometimes used. The concentration of a solid-phase tracer can also be measured by a capacitance probe if the tracer material has a different dielectric constant than the solid phase. In general, however, for solid and sometimes gas phases, some suitable radioactive tracer is convenient to use. The detection systems for a radioactive tracer (which include scintillation counters, a recorder, etc.) can be expensive. Some of the tracers for the gas, liquid, and solid phases reported in the literature are summarized in Table 3-1. 

The measurement of surface charges requires special capacitive probes that define the actual area being measured. In the measurement of bulk charges, often referred to as space charges, the extra dimension that defines the depth of charge in the material is usually probed by means of some kind of pulse that travels through the material. 

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