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A recording mercurial manometer for the pressure range 0–760 mm. of mercury
VACUUM Classified Abstracts -
II -
Vacuum Apparatus and Auxiliaries -
A Recording
0
Mercurial Manometer
-
GAUGES
_-
-
for the Pressure Range ~760
21
Sommaire : Un manom&re a colonne de mercure a BtB construit, pour l’enrbgistrement entre O-760mm. Hg pour Studier la reaction entre les m&aux et la vapeur d’eau.
0
47/11
mm. of Mercury
Unifed States. A simple and reliable recording manometer was required in .a series of experiments concerned with reaction phenomena between moderately active metals and water vapour which were to be followed by observing the increase of pressure caused by the hydrogen evolved. The pressure range to be covered was 0-600mm. Hg. As no suitable instrument was avallable commercially a new design was developed specially for the purpose. It consisted of a large bulb mercury manometer with a 6mm. diameter Pyrex tube 85 cm. long carrying in the centre a resistance wire (Nichrome V No. 24) which was part of a d.c. bridge circuit. At zero pressure the full length of the wire was included in the bridge circuit but as the pressure rose the effective length of the wire was gradually reduced. The change in resistance over the full pressure range was 4 ohm. The bridge was supplied by a stabilised power unit of 300 V. One leg consisted of a current limiting resistor and the manometer wire and the other leg of another current limiting resistor in series with a fixed resistor. The latter two determined the maximum zeroing sensitivity for the recording potentiometer incorporated in the circuit as the balance indicating device. In the particular case the following values were chosen : The potentiometer had a range of O-SO mV, the total current drawn was 15 mA, the manometer wire (full length) equalled 4 ohm, the current limiting resistor in the manometer leg = 24,000 ohm, the other current limiting resistor = 150,000 ohm and the fixed resistor = 25 ohm. A current of 12.5 mA passed through the manometer leg and when the effective length of the manometer wire was shortened the current changed in the proportion of 1 part in 6,000 over the entire pressure range. The current in the other leg was 2 mA which facilitated zeroing the pen of the recording potentiometer when the pressure was zero. The upper limit, 760 mm. pressure, was recorded at 50 mV. With slight modifications a manometer of this design can be used as a pressure control device.
Temperature-Stable
Capacitance
Abstract No. and Reference%
II
Cc&d.
21
-
continu des pressions
Article bv H. J Svec ‘and D. 9. Gibbs Kca. Sri. Insbun,. 24, March 1953 202-204
Pressure Gauges
!S/II
United I(ingdom. The author, engaged in the construction of capacitance pressure ‘gauges, found that instabilities observed were predominantly due to temperature changes. Generally, the characteristics of the gauge such as sensitivity, linearity and frequency response have been explored very fully but little has been published on temperature effects. In the present paper equations developed by other workers have been extended to account for the above-mentioned observations. The total capacity of a pressure gauge can be considered to be made up of three components : (a) The capacitance of the electrode to the diaphragm at zero applied pressure, (b) the ‘ stray ’ capacitances and (c) the change in capacitance due to a given applied pressure. (c) is determined by the nature of the diaphragm. A formula is given for the overall temperature coefficient of the total capacitance which serves as an indication of stability. The temperature coefficient of (0). the diaphragm capacitance, is the most important. Its value, in turn, is governed by three sets of conditions : Changes in area of the electrode and changes of gap size resulting from differential expansion, constraints acting in the diaphragm causing distortion and non-uniformity of the temperature in the gauge due, for example, to hot fluid impinging on one side. A theoretical treatment of these conditions, given in appendices to the paper, yields formulae useful for the assessment of major design features. In the second part of the paper the practical design of a capacitance gauge developed on the basis of the results of the theoretical considerations is described. The gauge was built for the pressure range 0-1Omm. of water. Its capacitance was fixed by design considerations at 100 pF. A stretched membrane made from 0.002 inch. steel shim was used as the diaphragm which had a sensitivity of 0.23 pF. per mm. of water and a total capacitance of 80 pF. Its overall temperature coefficient in the range of 10°C. around room temperature was only -100 p.p.m/“C.
Article by D. C. Pressev J. Sci. Ins&~ 30, Jn;~I958 _I
Sommaire : L’effet des changements de temperature sur les jauges de pression & capacitance est disc& thboriquement et la construction d’une jauge B coefficient de temp&ature sur la capacitance, faible, est d&rite.
A Diaphragm-Type
Capacitance-Type
Micromanometer
for Very Low Differential Pressures
United States. Until recently the limit of resolution for diaphragm micromanometers was 1 mm. Hg but Sibelcr and Corder0 have lately designed an instrument lowering the limit of resolution to 0.1 micron Hg. A similar instrument is described and illustrated in this report. It contains a corrugated diaphragm 0.001 inch. thick and 3 inch. diameter wide and is combined with a capacitance-type pick up and resonant-bridge carrier system of 0.005 micro-microfarad sensitivity. Details of the calibration method employed are given. ‘An Ascot Casella micromanometer was used for the purpose and the required pressure changes were effected with the help of a hypodermic syringe. The results of experimental calibrations are shown in 2 diagrams; one applying to an instrument with an electrode spacing of 0.017 inch, and the other to an electrode spacing of 0.0035 inch. If one side of the diaphragm is joined to a vacuum system the instrument can be used as an absolute pressure gauge and might provide a means of calibrating ionisation gauges. Sommaire : Description d’un micromanombtre a diaphragme du type a capacitance pour des basses pressions differentielles et convenable pour la mesure absolue de pressions de l’ordre de O.OOlmm. Hg.
A@il, 1953 Vol.
VCUX4U??Z III No. 2
49/H
F
January 1953 7 PP.
192
II -
Vacuum Apparatus and Auxiliaries -
A Recording
0
Mercurial Manometer
-
GAUGES
_-
-
for the Pressure Range ~760
21
Sommaire : Un manom&re a colonne de mercure a BtB construit, pour l’enrbgistrement entre O-760mm. Hg pour Studier la reaction entre les m&aux et la vapeur d’eau.
0
47/11
mm. of Mercury
Unifed States. A simple and reliable recording manometer was required in .a series of experiments concerned with reaction phenomena between moderately active metals and water vapour which were to be followed by observing the increase of pressure caused by the hydrogen evolved. The pressure range to be covered was 0-600mm. Hg. As no suitable instrument was avallable commercially a new design was developed specially for the purpose. It consisted of a large bulb mercury manometer with a 6mm. diameter Pyrex tube 85 cm. long carrying in the centre a resistance wire (Nichrome V No. 24) which was part of a d.c. bridge circuit. At zero pressure the full length of the wire was included in the bridge circuit but as the pressure rose the effective length of the wire was gradually reduced. The change in resistance over the full pressure range was 4 ohm. The bridge was supplied by a stabilised power unit of 300 V. One leg consisted of a current limiting resistor and the manometer wire and the other leg of another current limiting resistor in series with a fixed resistor. The latter two determined the maximum zeroing sensitivity for the recording potentiometer incorporated in the circuit as the balance indicating device. In the particular case the following values were chosen : The potentiometer had a range of O-SO mV, the total current drawn was 15 mA, the manometer wire (full length) equalled 4 ohm, the current limiting resistor in the manometer leg = 24,000 ohm, the other current limiting resistor = 150,000 ohm and the fixed resistor = 25 ohm. A current of 12.5 mA passed through the manometer leg and when the effective length of the manometer wire was shortened the current changed in the proportion of 1 part in 6,000 over the entire pressure range. The current in the other leg was 2 mA which facilitated zeroing the pen of the recording potentiometer when the pressure was zero. The upper limit, 760 mm. pressure, was recorded at 50 mV. With slight modifications a manometer of this design can be used as a pressure control device.
Temperature-Stable
Capacitance
Abstract No. and Reference%
II
Cc&d.
21
-
continu des pressions
Article bv H. J Svec ‘and D. 9. Gibbs Kca. Sri. Insbun,. 24, March 1953 202-204
Pressure Gauges
!S/II
United I(ingdom. The author, engaged in the construction of capacitance pressure ‘gauges, found that instabilities observed were predominantly due to temperature changes. Generally, the characteristics of the gauge such as sensitivity, linearity and frequency response have been explored very fully but little has been published on temperature effects. In the present paper equations developed by other workers have been extended to account for the above-mentioned observations. The total capacity of a pressure gauge can be considered to be made up of three components : (a) The capacitance of the electrode to the diaphragm at zero applied pressure, (b) the ‘ stray ’ capacitances and (c) the change in capacitance due to a given applied pressure. (c) is determined by the nature of the diaphragm. A formula is given for the overall temperature coefficient of the total capacitance which serves as an indication of stability. The temperature coefficient of (0). the diaphragm capacitance, is the most important. Its value, in turn, is governed by three sets of conditions : Changes in area of the electrode and changes of gap size resulting from differential expansion, constraints acting in the diaphragm causing distortion and non-uniformity of the temperature in the gauge due, for example, to hot fluid impinging on one side. A theoretical treatment of these conditions, given in appendices to the paper, yields formulae useful for the assessment of major design features. In the second part of the paper the practical design of a capacitance gauge developed on the basis of the results of the theoretical considerations is described. The gauge was built for the pressure range 0-1Omm. of water. Its capacitance was fixed by design considerations at 100 pF. A stretched membrane made from 0.002 inch. steel shim was used as the diaphragm which had a sensitivity of 0.23 pF. per mm. of water and a total capacitance of 80 pF. Its overall temperature coefficient in the range of 10°C. around room temperature was only -100 p.p.m/“C.
Article by D. C. Pressev J. Sci. Ins&~ 30, Jn;~I958 _I
Sommaire : L’effet des changements de temperature sur les jauges de pression & capacitance est disc& thboriquement et la construction d’une jauge B coefficient de temp&ature sur la capacitance, faible, est d&rite.
A Diaphragm-Type
Capacitance-Type
Micromanometer
for Very Low Differential Pressures
United States. Until recently the limit of resolution for diaphragm micromanometers was 1 mm. Hg but Sibelcr and Corder0 have lately designed an instrument lowering the limit of resolution to 0.1 micron Hg. A similar instrument is described and illustrated in this report. It contains a corrugated diaphragm 0.001 inch. thick and 3 inch. diameter wide and is combined with a capacitance-type pick up and resonant-bridge carrier system of 0.005 micro-microfarad sensitivity. Details of the calibration method employed are given. ‘An Ascot Casella micromanometer was used for the purpose and the required pressure changes were effected with the help of a hypodermic syringe. The results of experimental calibrations are shown in 2 diagrams; one applying to an instrument with an electrode spacing of 0.017 inch, and the other to an electrode spacing of 0.0035 inch. If one side of the diaphragm is joined to a vacuum system the instrument can be used as an absolute pressure gauge and might provide a means of calibrating ionisation gauges. Sommaire : Description d’un micromanombtre a diaphragme du type a capacitance pour des basses pressions differentielles et convenable pour la mesure absolue de pressions de l’ordre de O.OOlmm. Hg.
A@il, 1953 Vol.
VCUX4U??Z III No. 2
49/H
F
January 1953 7 PP.
192