Vacuum gauge

The Zimmerli vacuum gauge % covers a wide range of pressure (0-100 mm. Hg) and is depicted in Fig. 11, 23, 3. It is an improvement of the U-tube gauge (Fig. 11,  [c.113]

As with gases, there are no sharply defined limits for what should be considered a liquid under MS operating conditions, and the best guide with regard to use of mass spectrometers probably comes from the operating temperature range (10 to 30°C) of the instrument or any associated apparatus. A mass spectrometer inlet may be at atmospheric pressure or it may be under a high vacuum (10 to 10 mm of mercury). Clearly, introduction of a low-boiling liquid into the inlet of a system under high vacuum will lead to its rapid volatilization. It may even be that the pressure rise resulting from volatilization of a liquid becomes so great that the instrument shuts itself down to safeguard its vacuum gauges and ion detectors. It is worth recalling that even substances with a boiling point of 100°C or more will evaporate rapidly in a vacuum of l(h mm of mercury. The higher the boiling point, the less it is a problem. Liquids and even solids may well arrive at the mass spectrometer inlet in vapor form, as when they come from a gas chromatograph. Generally, the amounts of such emerging substances are very low, so, if the vacuum is high, transfer from the chromatographic column is easy through a heated line to the inlet or ion source of a mass spectrometer.  [c.279]

Gauge pressure is equal to absolute pressure minus barometric pressure. Absolute pressure is gauge pressure plus barometric pressure. If a gauge indicates, for example, that the pressure is 15 psig and the local barometric pressure is 14.7 psia, then the absolute pressure is 29.7 psia (205 kPa). Gauge pressure can be either positive or negative. When the term pressure gauge is used, the reference is almost always to a gauge that is used to measure positive pressures, ie, pressures that exceed local barometric pressure. A vacuum gauge is used to measure negative pressures. A compound gauge is designed to measure both positive and negative pressures and indicates gauge pressure and vacuum on the same scale. A negative gauge pressure indicates that the system is operating under a vacuum, ie, the absolute pressure is less than barometric. For systems that operate under negative pressures, ie, under vacuum, absolute pressure is equal to the barometric pressure minus the vacuum. If a gauge, for example, indicates —25 in. of mercury (—25 in. Hg), the local barometric pressure is 29.9 in. Hg, and the ambient temperature is 60°F, then the absolute pressure is 4.9 in. Hg (16.5 kPa).  [c.20]

Bourdon Tube. A Bourdon tube is made from a flattened or eUiptical tube, where one end is sealed, the other open to the process. Figure 3 illustrates the three basic designs of this sensing element. AH Bourdon tubes are based on the simple principle that a closed-end, flattened or eUiptical coiled tube tends to straighten out when a gas or a Hquid under pressure is aUowed to enter the tube. The Bourdon tube responds to the pressure difference between the inside and the outside of the tube. If a Bourdon tube is coimected to a system under vacuum, atmospheric pressure causes the tube to cud inward. Bourdon tubes are, therefore, used extensively in pressure gauges, in vacuum gauges, and in compound gauges.  [c.20]

The C-Bourdon tube (Fig. 3a) usually has an arc of 250°. The open end of the tube is fixed. The closed end of the tube, ie, the tip of the tube, is connected through a mechanical linkage to a pointer or a pen. The principal limitation of the C-design is tip travel. The degree of movement pet unit pressure change is small, and the design of the mechanical linkages requited for amplification can be quite complex. The spiral Bourdon (Fig. 3b) is made by winding the tube in a spiral of several turns, instead of the relatively short 250° arc of the C-design. This gives the spiral a much higher degree of movement per unit of pressure change. The hehcal Bourdon tube (Fig. 3c) has the same advantage and even more tip travel than the spiral (4). The C-Bourdon tube is more often used as the sensing element for a pressure gauge, a vacuum gauge, or a transmitter. Spiral or hehcal Bourdon tubes ate more likely to be used in receivers and recorders.  [c.21]

The pressure sensors discussed herein are reasonably accurate for measurement into the low vacuum region. Upon some modification, these sensors can be extended into the lower end of the range, to approximately 1.3 x 10 Pa (10 torr). Vacuum gauges ate required for accurate measurement of lower pressures.  [c.26]

Vacuum gauges may be broadly classified as either direct or indirect (10). Direct gauges measure pressure as force pet unit area. Indirect gauges measure a physical property, such as thermal conductivity or ionisation potential, known to change in a predictable manner with the molecular density of the gas.  [c.26]

Electromechanical monitors for steam sterilization include pressure, temperature, time-recording charts, and pressure—vacuum gauges. Most recording charts are also capable of displaying pressure—vacuum values. The temperature sensor is generally located in the chamber-drain line, considered to be the coolest area in the autoclave because air exits from the chamber via the drain line. There is no way of locating the sensors inside the packages being sterilized except under specialized test conditions.  [c.408]

If the gauge pressure at the suction flange is less than atmospheric, requiring use of a vacuum gauge, this reading is used for in Eq. (10-41) with a negative sign.  [c.900]

Again, if the discharge gauge pressure is below atmospheric, the vacuum-gauge reading is used for /jg in Eq. (10-43) with a negative sign.  [c.900]

A vacuum system typically consists of one or more pumps which are connected to a chamber. The former produces the vacuum, the latter contains whatever apparatus requires the use of the vacuum. In between the two may be various combinations of tubing, fittings and valves. These are required for the system to operate but each introduces other complications such as leaks, additional surface area for outgassing and added resistance to the flow of gas from the chamber to the pumps. Additionally, one or more vacuum gauges are usually connected to the system to monitor pressure.  [c.145]

Vacuum (Gauge) Below  [c.53]

Roper, D. L., and Ryans, J. L., Select the Right Vacuum Gauge, Chem. Eng., V. 96, No. 3, 1989.  [c.398]

This is sometimes made of mirror glass in order to eliminate the error due to parallax, t Manufactured by Edwards High Vacuum Ltd. This is essentially a form of McLeod gauge.  [c.113]

Vacuum system. Components associated with lowering the pressure within a mass spectrometer. A vacuum system includes not only the various pumping components but also valves, gauges, and associated electronic or other control devices the chamber in which ions are formed and detected and the vacuum envelope.  [c.430]

Dry ore toimage is measured by belt scales mounted along the conveyor belt line. These are continuous weighing devices and take into account the belt load and the belt speed. The output is a flow rate. An integrator in the scale calculates the total toimage. Slurry flow rates are measured using magnetic or ultrasonic flow meters (Fig. 24). Slurry densities are routinely measured by batch operation by collecting a representative slurry sample in a Hter vessel and weighing it on a density scale. Continuous pulp density measurement is made using a nuclear density meter (Fig. 25) or a gamma-gauge which measures the transmission of gamma rays from a radioactive source through the slurry using an ionization chamber-type detector. Transmittance is inversely proportional to the slurry density. Particle size is measured routinely, in a batch operation, by collecting a representative sample and using laboratory standard sieves. Numerous devices are also available for continuous particle size measurement. One of the more common devices uses the attenuation of ultrasonic energy that occurs on transmission through a slurry, eg, the PSM systems for on-line measurement (2). For fine particles, laser-based size analyzers, which are light-scattering devices, can be used, eg, the PAR-TEC system which operates as a scanning laser microscope (50) and the Microtrac system (34). Various other components of plant control and automation include the elaborate alarm systems and shutdown mechanisms for cmshers based on bearing pressure and temperature cmsher power and ore level grinding and classifier controls comprising ore feed rate, water addition rate, classifier feed rate and pulp density, particle size distribution, mill power, and load flotation controls comprising aeration rate, pulp and froth level reagents addition rates and pH and lime addition. Considerable effort is going into improving the performance of existing measurement devices and sensors, and developing new ones. One area of active work is in the development and implementation of reflable redox control systems for sulfide flotation circuits (51). Color (or vision) sensors for on-line analysis of flotation froths and slurries is also under development (50).  [c.417]

Inverted Bell-Type Pressure Element. An inverted beU manometer, iUustrated in Figure 2, consists of two inverted beUs immersed in oil. The oil provides a Hquid seal. The beUs are suspended from opposite ends of a balance beam and are arranged so that pressure, P, can be introduced under each beU. One of the lines is usually open to atmospheric pressure, the other to the pressure to be measured. The beU subjected to the higher pressure rises in the oil, tilting the beam which moves a pointer on a scale. This instmment responds to a pressure difference, AP, as small as 0.1 Pa (0.0004 in. H2O). The gauge ranges available range from 0—0.05 kPa (0—0.2 in. H2O) up to 0—3.7 kPa (0—15 in. H2O) pressure or vacuum. Inverted beU manometers are used for measuring very low positive pressures, such as those found in furnace kiln drafts and conveyor dryers (see Drying Furnaces, fuel-FIREd).  [c.20]

The development of thin-film and diffused semiconductor strain gauges represents significant advances in strain-gauge technology. A thin-film strain gauge is produced by depositing a thin layer of metal on a metal diaphragm by either vacuum deposition or sputtering (see Thin films). To produce thin-film strain-gauge transducers, first an electrical insulator such as a ceramic is deposited on the diaphragm (see Ceramics AS electrical materials). The strain-gauge alloy is deposited on the insulator. This technique produces a strain gauge that is moleculady bonded to the element, thus eliminating temperature effects and stress creep associated with organic adhesives. The result is long-term stabiUty, which is the principal advantage of thin-film strain-gauge technology.  [c.24]

Thermal conductivity gauges are simple and robust, but not very accurate. Accuracy quoted in instmment specifications is typically 20% of reading across the range 0.1—133 Pa (10 1 torr). Thermal conductivity gauges are generally used as pressure indicators, to monitor rather than measure system pressure. The advantages of these gauges include low cost, simplicity, and interchangeabiUty of the sensing elements. They ate well adapted for appHcations in which a single power supply and measuring circuit is used, with sensing elements located at different parts of the same vacuum system or on several different systems.  [c.27]

The earhest form of ion gauge, the triode gauge, looks much like a triode vacuum tube (Fig. 14a). The gauge consists of three electrodes in a hermetically sealed tube a filament surrounded by a grid wire helix and a large-diameter, soHd cylinder. The filament, typically tungsten, serves as the cathode. It is heated by an electric current, and electrons are released from the filament surface into the surrounding vacuum. Emission of electrons is controlled by controlling the electric current to the cathode. The grid serves as the anode and is set at a positive potential of 100—300 V with respect to the cathode. The grid attracts the electrons emitted by the cathode. The third electrode, the plate, is set at a potential of from —2 to —25 V with respect to the cathode. The plate, the ion collector, attracts positive ions generated by coUisions between the electrons emitted by the cathode and molecules of gas. The usual practice using commercial hot-cathode ionisation gauges is to precisely control the emission current to the cathode and measure pressure by measuring the ion current at the plate.  [c.27]

The accuracy of indirect-reading gauges is always a source of concern. This is especially tme of ionisation gauges, because the ionisation gauge is a particle density gauge. The ion current measured at the plate is a function of particle density and ionisation probabiUty. Particle density is proportional to pressure if, and only if, temperature is constant. Dry air or nitrogen is used in caUbrating ionisation gauges. These gauges must be recaUbrated when used to measure the pressure of other gases. The ionisation probabiUty depends on the gas species (14). Hot-cathode ionisation gauges are built to very demanding tolerances, and carbon contamination of electrodes over time compromises accuracy. In spite of these problems and under the less-than-ideal conditions that characterise industrial appHcation of these gauges, hot-cathode ionisation gauges are generally accurate to within 25% for measurements in high and very high vacuum. The various ultrahigh versions of the triode and Bayard-Alpert gauges are accurate to within an order of magnitude.  [c.28]

Pressure and Vacuum. Pressure is usually designated as gauge pressure, absolute pressure, or, if below ambient, vacuum. Pressures are expressed in pascals with appropriate prefixes. When the term vacuum is used, it should be made clear whether negative gauge pressure or absolute pressure is meant. The correct way to express pressure readings is "at a gauge pressure of 13 kPa" or "at an absolute pressure of 13 kPa."  [c.310]

A vacuum system can be stalled by gas leaks (4,6,24). Traditionally, leaks are categorized as real or virtual. A real leak refers to permeation processes or cracks or holes that allow external gas (air) to seep into the vacuum environment. Atmospheric gases such as helium and hydrogen permeate glass equipment, especially at elevated temperature. The noble gases do not permeate metals, but hydrogen does. Virtual leaks refer to gases that originate from within, eg, from trapped volumes, the gauges, pumps and the bulk and surface-phase species. For example, carbon in bulk stainless steel may precipitate along grain boundaries and then combine with surface oxygen to give CO, which is then desorbed into the gas phase (25). Proper instmments readily distinguish real leaks from virtual leaks.  [c.370]

In practice, it is often necessary to take readings from hot-filament ionization gauges or other devices. Figure 5 gives pump-down curves for six different types of pumping equipment on the same vacuum chamber (23). The shape of curve 1 indicates that a real leak could be responsible for the zero slope demonstrated by the Bayard-Alpert gauge (BAG). The shape of the other curves could result from a combination of real and virtual leaks.  [c.370]

Gauges. Because there is no way to measure and/or distinguish molecular vacuum environment except in terms of its use, readings related to gas-phase concentration ate provided by diaphragm, McCleod, thermocouple, Pitani gauges, and hot and cold cathode ionization gauges (manometers).  [c.375]

Ionization gauges (IG) do not give pressure in the gaseous phase but are set to provide readings proportional to the concentration of molecules in the gaseous and, to a lesser extent, the condensed phases. These concentrations are translated to units of gaseous pressure. The hot and cold cathode ionization gauges, such as those shown in Figures 13 and 14, provide information about vacuum environment as a host of parameters. Perhaps largely by trial and error, selection of a gauge readout indicates when to begin the process or experiment. Turning the gauge off and on provides the so-called flash-filament gauge response. When the filament is turned off, it cools, and molecules from the gaseous environment impinge and stick to the surface of the cooling filament. When the filament is turned on again and its temperature rises to incandescence, these molecules ate desorbed. Sufficient electrons are provided by the filament to indicate the gas-phase concentration increase from this desorbed material. An abmptly rising pip having a longer decaying tail can be recorded from the output of the gauge. The area under this desorption peak is a measure of the integrated pumping effect of the cold bare filament. The filament is bombarded by the free molecular gas over a ca 2- 7T soHd angle. The flux of particles striking the filament is given by where n is the molecular concentration in the gas phase and vl is the average velocity of this Maxwellian gas. By changing the power suppHed to the filament in its heating phase and varying the time interval when the filament is left cold, approximate but usefiil information can be obtained (13).  [c.375]

Fig. 16. Schematic representation of the vacuum furnace shown in Figure 15, where 1 is electrical feedthrough 2, viewport 3, vacuum-gauge hot-filament ioni2ation 4, air valve 5, valve 6, thermocouple vacuum gauge 7, thimble trap 8, demountable coupling 9, flexible line 10, two-stage Hquid-sealed mechanical pump 11, DP 12, water-cooled baffle 13, pneumatic valve having sealed bellows 14, linear motion feedthrough having sealed bellows and 15, blind-flange port (43). The graphic symbols used are among those contained in the American Vacuum Society Standard 7.1. IG = ionization gauge. Fig. 16. Schematic representation of the vacuum furnace shown in Figure 15, where 1 is electrical feedthrough 2, viewport 3, vacuum-gauge hot-filament ioni2ation 4, air valve 5, valve 6, thermocouple vacuum gauge 7, thimble trap 8, demountable coupling 9, flexible line 10, two-stage Hquid-sealed mechanical pump 11, DP 12, water-cooled baffle 13, pneumatic valve having sealed bellows 14, linear motion feedthrough having sealed bellows and 15, blind-flange port (43). The graphic symbols used are among those contained in the American Vacuum Society Standard 7.1. IG = ionization gauge.
Cahbration of bigb-vacuum gauges is described by Sellenger [Vacuum, 18(12), 645-650 (1968)].  [c.891]

In 1850, the Toepler pump was invented this is a form of piston pump in which the reciprocating piston consists of mercury it was followed in 1865 by the Sprengel pump, in which air is entrained away by small drops of mercury falling under gravity. In 1874, the first accurate vacuum gauge, the McLeod gauge, again centred around mercury columns, was devised. These and other dates are listed in a concise history of vacuum techniques (Roth 1976). The first rotary vacuum pump, the workhorse of rough vacuum, was not invented until 1905, by Wolfgang Gaede in Germany, and the first diffusion pump, invented by Irving Langmuir at GE, followed in 1916.  [c.405]

The various new vacuum pumps certainly made possible much faster and more efficient pumping, but the essential breakthrough came from two events the recognition that the older ionic vacuum gauges were drastically inaccurate, and the further recognition that UHV systems needed to be made from metal, with little or no glass and no organic greases, and that the systems had to be bakeable.  [c.407]

Vacuum in process systems refers to an absolute pressure that is less than or below the local barometric pressure at the location. It is a measure of the degree of removal of atmospheric pressure to some level between atmospheric-barometer and absolute vacuum (which cannot be attained in an absolute value in the real world), but is used for a reference of measurement. In most situations, a vacuum is created by pumping air out of the container (pipe, vessels) and thereby lowering the pressure. See Figure 2-1 to distinguish between vacuum gauge and vacuum absolute.  [c.128]

Figure. 3-6 shows average vacuum-load curves for several engine models with fourcycle engines of two or more cylinders constructed by six representative engine manufacturers [3]. These curves cannot be used for supercharged or turbocharger engines. Vacuum readings are obtained with a conventional vacuum gauge, containing a dial graduated in inches of mercury. The intake manifold vacuum reading is taken first with the engine running at normal speed with no load and then with the engine running at normal speed with normal load. The curve selected is the one which, at no load, most closely corresponds to the no-load intake manifold vacuum reading. The point on the curve is then located with the ordinate corresponding to the reading taken at normal loading. The abscissa of this point gives the percentage of full load at which the engine is operating. For instance, if the no-load reading is 17 in. Hg and  [c.396]

Type J thermocouples (Table 11.58) are one of the most common types of industrial thermocouples because of the relatively high Seebeck coefficient and low cost. They are recommended for use in the temperature range from 0 to 760°C (but never above 760°C due to an abrupt magnetic transformation that can cause decalibration even when returned to lower temperatures). Use is permitted in vacuum and in oxidizing, reducing, or inert atmospheres, with the exception of sulfurous atmospheres above 500°C. For extended use above 500°C, heavy-gauge wires are recommended. They are not recommended for subzero temperatures. These thermocouples are subject to poor conformance characteristics because of impurities in the iron.  [c.1216]

A mass spectrometer has several integrated instruments that provide feedback information on how it is functioning. For example, the vacuum system is monitored by an ion gauge that gives out an electrical signal proportional to the vacuum being achieved. Thus, the computer can check this voltage routinely, and, if it finds a reading indicating a fault, it can draw it to the attention of the operator or, if the fault is serious, the computer can shut down the electronic components of the spectrometer to prevent them from being damaged. If, for instance, the pressure in an electron ionization source rises too high, the filaments will bum out early detection warning of the imminence of such a state is invaluable in avoiding time-consuming repairs. This type of checking is performed routinely, and, because of the speed of a computer, it can be carried out on a very short cycle time (e.g., once a second). Similarly, other parts of a mass spectrometer are routinely checked on a cyclical basis. For many faults, programming has reached a stage where the computer, having detected a fault, can diagnose it and report it to the operator.  [c.322]

In the unsaturated 2one, measurement of the fluid head is a bit more complex, because the fluid pressures are less than atmospheric, and therefore, fluid does not rise above the point of measurement in a monitoring well, ie, / is negative. Instead, a tensiometer such as that shown in Figure 2 may be used to determine the soil water suction. A tensiometer consists of an airtight, water-filled tube having a porous cup at the base. After insertion into the soil, moisture exits the tensiometer while hydraulic equiUbration is achieved with the surrounding unsaturated soil. As moisture exits, a vacuum is created in the evacuated space at the upper portion of the tensiometer. When the suction created in the tensiometer is equivalent to the negative pressure head in the surrounding soil, equiUbration has been achieved and the corresponding pressure can be read on the tensiometer gauge. Other set-ups that may be used to evaluate the pore fluid pressure in the unsaturated 2one include soil moisture blocks, thermocouple psychrometers, y-ray attenuation, and nuclear moisture  [c.402]

Visual Inspection and Optical Tests. Direct visual inspection and examination using optical aids and gauges is the most common of all forms of nondestmctive tests. Microscopic, telescopic, and electronic aids to vision include borescopes and magnifiers. These devices are appHed for inspecting inaccessible areas within turbine engines and along the internal length of long tubes. Corrosion, distortion, and general weld quaUty may be detected using these techniques. Additionally, typical go—no go gauges may be used for assuring dimensional quaUty in welds (3). Visual examination of welds also may locate common defects such as unfilled craters, undercutting, overlap, and incomplete penetration. Quantitative measurements utili2e geometrical optics, stroboscopic tests, spectrographic comparators, densitometers, refractometers, interferometers, tests for thickness of thin layers, phase-contrast techniques, and tests employing polari2ed light and measurements of birefringence. Advanced techniques include light section, schlieren (shadow), and diffraction methods of optical imaging and measurements. The effects of light scattering are used in the Eberhardt fine thread test, the dual pinhole fine stmcture test, and wave front reconstmction techniques for extreme magnification, ie, up to 10 times enlargement reconstmcted from an x-ray diffraction pattern (see Microscopy).  [c.124]

Absolute pressure is pressure measured relative to a perfect vacuum, an absolute 2ero of pressure (2). Like the absolute 2ero of temperature, perfect vacuum is never reali2ed in a real world system but provides a convenient reference for pressure measurement. The acceptance of strain gauge technology in the fabrication of pressure sensors is resulting in the increased use of absolute pressure measurement in the CPI (see Sensors). The pressure reference  [c.19]

Capacitance Manometers. Capacitance manometers were first used in research laboratories in the early 1950s. The development of capacitance manometers designed specifically for the harsh environments that characterize chemical processes is, however, a more recent development. The near-phenomenal accuracy of capacitance manometers, typically 0.10% of a reading >13.3 Pa (>0.1 torr) to 3% of a reading at 10 Pa (lO " torr), excellent linearity over a wide range of pressures, and the development of sensors that ate mgged and teUable, increasingly makes this the technology of choice for vacuum measurements in the range 10 -10 Pa (10 -10 torr). Capacitance manometers ate mgged for two reasons. Gauge electronics never come in contact with the process, and the sensor body and metal diaphragm ate fabricated from stainless steel. Monel, Inconel, or other high nickel alloys.  [c.26]

Pressure. Pressure, defined as force per urht area, can be expressed as an absolute or relative value. Although atmospheric pressure constantiy ductuates, a standard value of 101.3 kPa (14.7 psia) has been assigned as the accepted value at sea level. The "a" in the psia stands for absolute, ie, the pressure is 14.7 psi (101.3 kPa) above zero pressure or a vacuum. Most ordinary pressure-measuring instmments do not measure tme pressure, but rather a pressure relative to the barometric or atmospheric pressure. This relative pressure is called gauge pressure. The atmospheric pressure is defined to be 1 psig, in which the "g" indicates that it is relative to atmospheric pressure. Vacuum is the pressure below atmospheric pressure and is, therefore, a relative pressure measurement as well. The relationship between absolute and relative pressure is shown in Figure 3 (see Pressure MEASUREMENT Vacuum technology).  [c.310]

The role, design, and maintenance of creepproof barriers in traps, especially those in oil DPs, remain to be fully explored. In general, uncracked oil from a DP is completely inhibited from creeping by a surface temperature of <223 K. On the other hand, a cold trap, to perform effectively in an ordinary vacuum system, must be <173 K because of the vapor pressure of water, and <78 K because of the vapor pressure of CO2. For ultracontroUed vacuum environments, LN temperature or lower is required. CO2 accumulation on the trap surface must be less than one monolayer. The effectiveness of a LN trap can be observed by the absence of pressure pips on an ionization gauge when LN is replenished in the reservoir.  [c.378]

See pages that mention the term Vacuum gauge : [c.271]    [c.53]    [c.394]    [c.106]    [c.113]    [c.113]    [c.869]    [c.207]    [c.371]   
Industrial ventilation design guidebook (2001) -- [ c.1446 ]