Vacuum measuring systems

The total pressure during freeze-drying may be measured by several methods, although only two are mostly used heat conductivity and the membrane pressure difference gauge. Their operating principles and their advantages and disadvantages are described below. 

Measuring side 2, deflector/protective shield 3, welded diaphragm 4, electrodes  

electrode leadth roughs 6, getter pump to maintain a low reference pressure 7, reference side of very high vacuum (1 x lCr7 mbar). 

The sensors are manufactured as differential or absolute pressure sensors. The differential pressure sensors are connected on both sides to absolute pressure sensors, of which the difference between the two pressures is to be measured. They are then evacuated down to a pressure lower than 1 x 10 7 mbar on one side (a chemical getter protects the vacuum of 10 7 mbar from residual degassing). 

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 vacuum measurement systems used in the high and ulfrahigh regimes it... 

Note that the vacuum measurements of 27 inches Hg and 14 inches Hg are expressed in the vacuum measurement system typically used in American refineries where ... 

Adsorption isotherms conventionally have been determined by means of a vacuum line system whereby pressure-volume measurements are made before and after admitting the adsorbate gas to the sample. For some recent experimental papers, see Refs. 24 and 25. 

O When cakes tend to crack under vacuum measures such as a fiapper, compression blanket or pressure roll may assist in sealing the cracks thus avoiding loss of vacuum. When such measures are used it is necessary to make sure that the belt supporting system can take these extra vertical loads. 

Vacuum chamber with tempered shelves 2, container with probe 3, lift for shelves 4, condenser 5, lockgate 6, balance in the lock 7, vacuum pump for the lock 8, glove box 9, Karl-Fischer measuring system 10, pressure controlled vacuum pump 11, manipulator 12, tempered medium (Fig. 1 from [3.30]). 

The exposed HS-MOTSS copolymer films were dip-developed in solvent followed by baking at 50-80 °C in vacuum for about 30 min. E-beam dose matrice images were developed in chlorobenzene for 30 sec ion beam test exposures were developed in methyl isobutyl ketone for 30 sec. The thicknesses of the films were measured with a Nanospec/AFT microarea film thickness measuring system. 

The best-known design of a diaphragm vacuum gauge is a barometer with an aneroid capsule as the measuring system. It contains a hermetically sealed, evacuated, thin-walled diaphragm capsule made of a copper-beryllium alloy. As the pressure drops, the capsule diaphragm expands. 

The variable C is the vacuum gauge constant of the measuring system. For... 

In addition to the conventional ionization gauge, whose electrode structure resembles that of a common triode, there are various ionization vacuum gauge systems (Bayard-Alpert system, Bayard-Alpert system with modulator, extractor system) which more or less suppress the two effects, depending on the design, and are therefore used for measurement in the high and ultrahigh vacuum range. Today the Bayard-Alpert system is usually the standard system. 

Fig. 3.16 Schematic drawing of the ebctrode arrangement of various bnization vacuum gauge measuring systems...

The outside temperature must be taken into account and above all it is necessary to avoid hot kilns, furnaces or stoves or other sources of intense radiation which generate an ambient temperature around the measurement system which lies above the specific acceptable value. Excessive ambient temperatures will result in false pressure indications in thermal conductivity vacuum sensors. 

It is not fundamentally possible to keep the measurement system in a vacuum gauge from becoming soiled. Thus it is necessary to ensure that... 

Vacuum extraction alone is limited to treating unsaturated soils, and successful remediation is contingent upon factors such as soil properties and the volatility of the contaminants. Ideally, measured soil permeabilities should range between 10 " and 10 cm/sec, and contaminants should have a Henry s constant of 0.001 or higher. Also, sites with complex stratigraphy or contaminant distributions may require pilot demonstrations prior to the full implementation of a vacuum extraction system. 

Many types of vacuum adsorption apparatus have been developed and no doubt every laboratory where serious adsorption measurements are made has equipment with certain unique features. The number of variations are limited only by the need and ingenuity of the users. However, all vacuum adsorption systems have certain essential features, including a vacuum pump, two gas supplies, a sample container, a calibrated volume, manometer and a coolant. 

A low temperature nitrogen sorption was carried out on an automated physisorption instrument (ASAP 2000, Micromeritics Instrument Corporation). Before the measurement, the sample was degassed at 350 C for 4-5 h until the vacuum of system was better than 0.67 Pa. The data for micropore were obtained from t-plot, and those for mesopore and distribution of mesopore were calculated by BJH method (using desorption curve). The single point total pore volume at high relative pressure was taken as the total volume. 

A very convenient way of detecting and measuring leaks is to use a tracer gas (such as He) and a selective tracer gas detector, such as a helium leak detector. In addition to the mass spectrometer, MSLD include a high vacuum pumping system of definite pumping speed. 

The easiest way to see a quantitative vacuum measurement of a system is to look at a dial and read it. This direct reading can be done with mechanical gauges. The surface of mechanical gauges that come in contact with gases within a vacuum system can be made out of metal or glass (borosilicate or quartz), both of which can be fairly impervious to chemical attack. ... 

---