Capacitance manometers

Chase [2.32] presents an alternative method to monitor and control the freeze drying process by measuring the flow of nitrogen to keep the operation control pressure, pc, constant. The Mass Flow Controller (FMC) consists of a proportional valve, an integral flow meter and a capacitance manometer (CA). The CA measures the total pressure in the plant, the valve opens, if the pressure gets below the preset value and vice versa. The flow of... 

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

This highly sensitive calorimeter needs to be connected to a sensitive volumetric system in order to determine accurately the amounts of gas or vapor adsorbed. A schematic representation of the whole assembly is shown in Figure 13.4 [147]. The volumetric determination of the adsorbed amount of gas is performed in a constant-volume vessel linked to a vacuum pump. The apparatus consists of two parts the measuring section equipped with a capacitance manometer, and the vessels section that includes the cells placed in the calorimeter (a sample cell in which the adsorbent solid is set, and an empty reference cell). 

Water activity (aw) is the ratio of the partial vapor pressure of water above a solution to that of pure water at the same specific temperature. It plays an important role in evaluating the microbial, chemical, and physical stability of foods during storage and processing. The vapor pressure in the headspace of a food sample can be measured directly by a manometer. A manometer has one or two transparent tubes and two liquid surfaces where pressure applied to the surface of one tube causes an elevation of the liquid surface in the other tube. The amount of elevation is read from a scale that is usually calibrated to read directly in pressure units. Makower and Myers (1943) were the first to use this method to measure vapor pressure exerted by food. Later, the method was improved, in terms of design features of the apparatus, by various scientists (Taylor, 1961 Labuza et al., 1972 Lewicki, 1987). Trailer (1983), Lewicki (1989), and Zanoni et al. (1999) used a capacitance manometer instead of a U-tube manometer for the measurement of vapor pressure. Lewicki et al. (1978) showed that the precision and reproducibility of the method can be improved by the simultaneous measurement of the water vapor pressure and temperature of the food sample. The method is reviewed in detail by Rizvi (1995) and Rahman (1995). 

Vapor pressure manometer apparatus consisting, e.g., of sample flask, desiccant flask, U-tube, manometric fluid (such as Apiezon B, from Sigma), and vacuum pump (Fig. A2.4.1) or similar apparatus with capacitance manometer... 

The vapor pressure manometer (VPM) provides a means for rapid determination of water activity. The method was suggested by Mak-ower and Myers (1943) to measure water vapor pressure exerted by food. This method was improved by Taylor (1961), Labuza et al. (1972), and Trailer (1983). Sood and Heldman (1974), Labuza et al. (1976), and Lewicki et al. (1978) studied design features, accuracy, and precision of the VPM. Trailer (1983) and Zan-oni et al. (1999) discussed the design and setup of a water vapor pressure capacitance manometer. 

Zanoni, B., Peri, C. Giovanelli, G., and Pagliarini, E. 1999. Design and setting up of a water vapor pressure capacitance manometer for measurement of water activity. J. Food Sci. 38 407-423. 

Canola oil, composition, 474 (table) Capacitance, in water activity measurement, 67-70 Capacitance manometer vs. U-tube manometer, 61,64 Capacitor model in interface studies, 624-625 Carbazole, 737 Carbohydrates... 

In the second manifold, the O2 is quantitatively converted to CO2 by combustion. The reaction occurs over several minutes by recirculation of the gas over Pt/graphite at 900°C. The C02 produced is condensed into a cold finger as it is formed the reaction is monitored through the pressure changes. Once the conversion is complete, the CO2 is transferred to second cold finger and its pressure determined using a capacitance manometer or strain gauge. The quantity of CO2 is directly related to the quantity of O2 present in the reaction solution and the isotope content is... 

All adsorptions were performed in a glass vacuum system. The pressures were measured with an MKS capacitance manometer. 

All reductions were carried out on a glass vacuum system under static H2 (Linde 99.999%) which was dried by passing through Drierite and molecular sieves prior to exposure to the sample. H2 uptakes were monitored using a capacitance manometer (MKS Instruments Inc.) N2 isotherms at 77 K were performed on the same vacuum system using pre-purified grade N2 (Linde) which was dried prior to use. Oxidations were performed under flowing 02 (Linde 99.999%) at 773 K and under static O2. The samples were evacuated at 623 K to a residual pressure of less than 5 X 10 5 torr prior to reduction or N2 isotherm measurements. 

Alternative Manometer Gauges. Alternatives to a mercury manometer are capacitance and magnetic reluctance gauges and also solid-state strain gauges. In a capacitance manometer, the pressure is sensed by the deflection of a membrane that is one... 

When the heat-pipe Is In a steady state the pressure of the metal vapor Is equal to that" of the buffer gas. The vapor pressure In the Isothermal zone Is thus determined by measuring the buffer gas pressure with an MKS Baratron capacitance manometer. 

All plasma exposures were carried out in an IPC (International Plasma Corporation) 2005 capacitance-coupled barrel reactor at 13.56MHz. The reactor was equipped with an aluminum etch tunnel and a temperature controlled sample stage. Pressure was monitored with an MKS capacitance manometer RF power was monitored with a Bird R.F. power meter and substrate temperature was measured with a Fluoroptic thermometer utilizing a fiber optic probe which was immune to R.F. noise. 

It is obvious that n and have to be determined accurately, n is usually determined by measuring the pressure, for example with a capacitance manometer such as a baratron, taking care to allow for temperature differences between the gas cell and the measuring region (Blaauw et al, 1980). Usually one has an effusive molecular flow through the entrance and exit apertures, which leads to large density gradients in the gas, and the product mf in the exponent of (2.10) has to be replaced by... 

The steam feeding of the chamber is under the full control of the programmable logic controller (PLC) and data acquisition is achieved by the SCADA system during sterilization cycle control. Vacuum gauges are adapted to function in saturated steam and ambient conditions (MKS capacitance manometer 621). 

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