fDVacuum Pressure Measurement �===Pressure Gauges Vacuum Pressure Introduction The definition of vacuum is an area void of matter and a partial vacuum is any pressure lower than the local atmospheric pressure being 760 Torr at sea level. Obtainable vacuum for process applications and laboratory experiments range from atmospheric pressure all the way down to 10-12 Torr. Vacuum pressure is often labeled by terms rough vacuum(below atmospheric pressure to 10-3 Torr), high vacuum(10-3 to 10-9Torr), and ultra-high vacuum(< 10-9 Torr). These terms can be confusing to a new comer to vacuum technology since high vacuum equals low pressure. There is a direct Vacuum Reference Chart mm in in PSIA connection between Torr I Hg A�soluteI Feet Miles I Meters I Hg Vacuum 1 Hg Absolute 1 I Pa I Bar 1 atm t h e s e vacuum I 1.09 1.09 150,000 28.4 45,720 29.877 0.04 0.02 150 0.00146 o.oo terminologies and I altitude, that is, low 13 13 90,000 17.1 27,459 29.4 0.52 0.26 1760 0.01733 0.02 1 pressure occurs at high 34 34 70,000 13.3 21,357 28.595 1.33 0.65 4490 0.04533 0.04 altitude,(figure 10-1 to 1 the right) shows a 69 69 55,000 10.4 16,781 27.208 2.71 1.33 9170 0.09199 0.09 87 87 50 000 9.5 15 255 26A76 3.44 1.69 11650 0.11599 0.11 vacuum reference 111 111 45,000 8.5 13,730 25.545 4.38 2.15 14820 0.14799 0.15 chart that displays 141 141 40 000 7.6 12 204 24.362 5.56 2.73 18820 0.18798 0.19 vacuum pressure at 179 179 35,000 6.6 10,679 22.86 7.06 3.47 23930 0.23865 0.24 226 226 30,000 5.7 9153 21.017 8.90 4.3Z. 30130 0.30131 0.30 different altitudes. The 282 282 25,000 4.7 7628 18.8 11.12 5.46 37650 0.37597 0.37 350 350 20,000 3.8 6102 16.16 l3.76 6.76 46610 0.46663 InternationalSystem of ::2& Units (abbreviated 429 429 15,000 2.8 4577 13.03 16.89 8.29 57160 0.57195 0.56 522 522 10,000 3050 9.34 2� 10.10 69M2.,. 0.6 0.69 51) - 1.:2.... for pressure is the � 543 543 9000 1.7 2746 1- 8.53 21.39 10.50 I-72400 0.72394 0.71 Pascal(Pa) but vacuum 564 564 8000 1.5 2441 7.69 22.23 10.91 75220 0.75194 0.74 586 586 7000 1.3 2136 6.82 23.10 11.34 78190 0.78127 0.77 pressure is often 609 609 6000 1.1 1831 5.93 23.99 11.78 81220 0.81193 0.80 reported in units of 633 633 5000 0.95 1526 5.02 24.90 12.23 84330 0.84393 0.83 Torr, Bar, atmosphere, 644 644 4500 0.86 1373 4.55 25.37 12.46 85910 0.85859 0.85 656 656 4000 0.76 1220 4.08 25.84 12.69 87490 0.87459 0.86 pounds per square inch 669 669 3500 0.66 1068 3.59 26.33 12.93 89150 0.89192 0.88 absolute (PSI A), 681 681 3000 0.57 915 3.1 26.82 13.17 90810 0.90792 0.90 millimeters of mercury 694 694 2500 0.47 763 2.6 27.32 13.41 92460 0.92525 0.94 706 706 2000 0.38 610 2.1 27.82 13.66 94190 0.94125 0.93 absolute (mmHg), and 719 719 1500 0.28 458 1.59 28.33 13.91 95910 0.95859 0.95 inches of mercury 732 732 1000 0.19 305 1.06 28.86 14.16 97630 0.97592 0.96 vacuum (in H g). 746 746 500 0.09 153 0.54 29.38 14.43 99490 0.99458 0.98 760 760 0 Sea Level 0 0 29.92 14.70 101330 1.01325 1.00 Vacuum technology is globally used in FIG. 10-1 numerous industrial Lower Air Pressure a n d scientific Perfect Vacuum = 0 Torr Pressure Low Density Decreases with applications, many of Outer Space= 1 x 10·6 to <3 x 10"17 Torr these areas of VI Altitude expertise use different x ..5!! Extremely High Vacuum = 1 10"12 Torr ::::1 656,000 Ft. (.0075 Torr) units to report vacuum u x x Q) __;_; 150,000 Ft. (1.09 Torr) pressure. Ultra High Vacuum = 1 10-9 to 3 10"12 Torr 0 � 100,000 Ft. (8 Torr) High Vacuum = 1 x 10-3 to 3 x 10-9 Torr 10,000 Ft. (522 Torr) Higher 7,000 Ft. (586 Torr) x Pressure 5,000 (633 Torr) Rough Vacuum= 760 to 3 10-3 Torr High Ft. Density 0 (760 Torr) Atmospheric Pressure= 760 Torrat seal Level - Ft. 10·1 www.idealvac.com (505)872-0037 Vacuum Pressure Measurement f]) ·�-=============Pressure Gauges Vacuum Pressure Gauge Introduction It is often very important to know the vacuum pressure. When building a new vacuum system, pressure measurement equipment is typically second on the list of required items, just after the vacuum pump requirements have been specified. Vacuum goes from 760 to 10-12 Torr, more than 1015 powers, and it is easy to understand why one type of vacuum pressure sensor cannot measure the complete range. It often requires two or more different sensors to cover from atmosphere to ultra-high vacuum. We will limit our vacuum gauge discussion here to mainstream modern vacuum gauge technologies, (see figure 10-2 below) which includes the vacuum gauges; Bourdon, Capacitance Manometer, Thermocouple, Convection­ Enhanced Pi rani, Hot Cathode Ionization, Cold Cathode Ionization, and Combination Full-Range gauges. UHV High Rough IIIII( Vacuum I Vacuum I Vacuum Pressure (Torr) 1 o-13 10"11 10"9 1 o-7 1 o-s 1 o-3 10"1 101 103 I I I I I I I I I I I I �ou dol) Gauge Capacitance • Thermocouple Manometer Rough Vacuum e:apacitance Manometer 760 to 1x10-3 Torr Ciovectron Pi�ani • I I I I I I I I I � I � o UHV Models & Cold Catho.de hiwerted Mag:netrron • I : Comb]nat!on F.uii-Range r Hot Cathode lo� Gauge• � Bourdon Gauge Rough Vacuum 1 o-11 10"9 1 o-7 1 o-s 1 o-3 1 o-1 101 103 105 760 to 1x10-1 Torr Pressure (Pa) FIG. 10-2 Rough Vacuum 760 to 1x10-3 Torr Full Range Combination [?����CLD�� Rough to High Vacuum 100 to 1x10-9 Torr ��CLD��� r Cold Cathode Inverted Magnetron High Vacuum 1x10-3 to 1x10-12 Torr www.idealvac.com (505)872-0037 10·2 fDVacuum Pressure Measurement �Pressure Gauges (Cont.JVacuum Pressure Gauge Introduction These gauges can be grouped into two categories labeled as roughing and high vacuum gauges. Roughing gauges are used to measure vacuum pressure provided by the mechanical roughing pumps in the 760 to 1x10-3 Torr pressure range, which includes, Bourdon, Capacitance Manometer, Thermocouple, and Convection-Enhanced Pirani gauges. High and ultra-high vacuum gauges are used to measure pressure from high vacuum pumps in the 10-3 to 10-12 Torr pressure range, which includes, hot cathode and cold cathode ionization gauges. There are modern full-range gauges available that measure vacuum pressure from atmosphere to around lQ-9 Torr. These wide-range combination gauges include both a roughing and high vacuum sensors all built into one. They use the roughing sensor to measure vacuum pressure until the pressure is low enough to turn on the high vacuum sensor. These gauges crossover seamlessly from roughing to high (MeasuresDirect Actual Gauges Pressure) vacuum so that un-interrupted vacuum pressure data is displayed to the instrument user. There are full-range gauges available that even compose three measurement technologies into one multi-sensor. Some examples of the full range gauges are the, (1) Convention­ Capacitance Bourdon Enhance Pirani & Hot Cathode,(2) Convention-Enhanced Pirani & Cold Manometer Tube Cathode, (3) Capacitance Diaphragm, Pirani, & Hot Cathode. Full­ range combination vacuum gauge sensors are compact and easy to use but are more expensive than the individual classical vacuum Indirect(Measures Gas Gauges Properties) sensors. Therefore, full-range gauges are often used on clean dry vacuum applications with little chance of sensor contamination and where sensor replacement frequency would be low. Pi rani Hot&Cold There are two basic designs of gauges, those that measure vacuum Thermocouple Cathode pressure directly and those that indirectly provide a pressure reading, (see figure 10-3 to the side.) The direct gauges measure the actual vacuum pressure, force per unit area, which include the Bourdon and Basic Design of Pressure Guages Capacitance Manometer. The indirect gauges calculate the vacuum pressure by measuring a physical property of the gas which changes in FIG. 10-3 a predictable manner as gas density changes. The physical property is pressure depend so that if the gas-type and temperature are known then the vacuum pressure can be calculated. The physical property can be energy transfer as heat through the vacuum (Pirani and thermocouple gauges) or ion particle current (hot and cold cathode ionization gauges). The important factor here is, indirect pressure gauges must be calibrated for the gas-type used in the vacuum application, because indirect gauges will provide different pressure readings for different gases at the same pressure.