Stabilised ion gauge control unit

VACUUM Classified A b s t r a c t s

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Vacuum

Apparatus

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Abstract No. and References

11/II

A Compression Vacuum Gauge with a Large W o r k i n g R a n g e Australia. A c o m p r e s s i o n t y p e v a c u u m g a u g e is described w h i c h differs f r o m t h e c o n v e n t i o n a l Mcleod gauge b y h a v i n g a capillary U - t u b e m a n o m e t e r in place of t h e u s u a l closed m e a s u r i n g capillary. ~'he o t h e r e n d of t h e U - t u b e m a n o m e t e r is r e t u r n e d t o t h e v a c u u m s y s t e m . T h e pressure is m e a s u r e d b y r e a d i n g t h e difference in h e i g h t on t h e t w o l i m b s of t h e m e r c u r y m a n o m e t e r . T h e u s u a l b u l b is cylindrical a n d b y taki.'ng t h e m e r c u r y u p to different m a r k s on t h i s cylinder several c o m p r e s s i o n ratios are o b t a i n a b l e w i t h one gauge. T h e a d v a n t a g e s claimed are t h a t a large r a n g e of pressure c a n be covered. T h e U - t u b e m a n o m e t e r c a n be filled w i t h a low v a p o u r p r e s s u r e oil to increase t h e s e n s i t i v i t y of t h e gauge. Sommaire : Le d ~ v e l o p p e m e n t d ' u n e j a u g e d u t y p e A c o m p r e s s i o n e s t d~crit, celle-ci 6 t a n t bas6e s u r le principe de McLeod, m a t s c o u v r a n t u n d o m a i n e p l u s ~tendu q u e cette demi~re.

Paper by N. A. Florescu Invest. Phys. No. 3. 4 pp. 12/H

The Pirani Gauge United States. The. w o r k i n g principle of t h e P i r a n i g a u g e a n d i m p r o v e m e n t s of t h e original design proposed b y K e r s t e n , B r i n k m a n , R i t t u e r a n d V o n U b i s c h are reviewed. T h e g a u g e h a s t h e following m a i n a d v a n t a g e s : (1) I t is suitable for t h e m e a s u r e m e n t of low pressures. (2) I t gives a q u i c k response a t low pressures, ff a t h i n f i l a m e n t is used. (3) F i l a m e n t m a t e r i a l s are k n o w n w h i c h p e r m i t its o p e r a t i o n in corrosive a t m o s p h e r e s a n d (4) a wide r a n g e of p r e s s u r e s c a n b e covered if t h e design is suitable. I t s m a i n d i s a d v a n t a g e s are : (1) T h e zero p o i n t t e n d s to s h i f t a n d (2) r a d i a t i o n interferes w i t h t h e w o r k i n g of t h e g a u g e a t p r e s s u r e s below 10-3ram. Hg. I t s n o r m a l r a n g e is l0 -4 to 10-Xmm. Hg, b u t V o n U b i s c h h a s described a design w h i c h increases t h e r a n g e to 5 0 m m . Hg. R i t t n e r b u i l t a gauge, described in t h e article, w i t h a s e n s i t i v i t y of 1 × 10-4mm. H g a t low p r e s s u r e s a n d =t= 0 . 3 5 m m . a t 1 5 m m . Hg. T h e a u t h o r s r e p o r t on t h e p e r f o r m a n c e of a g a u g e w h i c h t h e y cons t r u c t e d t h e m s e l v e s . A t u n g s t e n or p l a t i n u m f i l a m e n t 16 cm. long 0.025ram. thick, h a i r p i n s h a p e d a n d k e p t t a u t b y a glass w e i g h t h o o k e d over t h e loop of t h e wire, was s u s p e n d e d in a t u b e of 9 m m . d i a m e t e r w h i c h w a s i m m e r s e d in a D e w a r vessel c o n t a i n i n g c r u s h e d ice a n d water. D u r i n g e x p e r i m e n t s in a h y d r o g e n a t m o s p h e r e at p r e s s u r e s b e t w e e n l0 -e a n d 10-atom. H g t h e p l a t i n u m wire took a c u r r e n t of 26 m A a n d showed a s e n s i t i v i t y of 6.6 volt per ram. H g w h e r e a s t h e t u n g s t e n wire required a c u r r e n t of 40 m A a n d s h o w e d a s e n s i t i v i t y of 5.1 volts per m m . Hg. T h e zero position w a s d e t e r m i n e d b y h e a t i n g t h e f i l a m e n t a t O p r e s s u r e for ½ h o u r a n d t a k i n g several voltage r e a d i n g s until a c o n s t a n t v a l u e was obtained. F o r t h e d e t e r m i n a t i o n of t h e zero s h i f t t h e g a u g e fitted w i t h t u n g s t e n wire was h e a t e d a t 40 m A a n d O pressure. A f t e r 7 h o u r s a drift u p to 0.1% w a s observed. Allowing for a zero shift of t h i s order t h e calibration c u r v e s were reproducible. Calibration c u r v e s for xenon, c r y p t o n , neon, argon, helium, h y d r o g e n a n d n i t r o g e n are s h o w n for b o t h increasing a n d decreasing pressure in t h e r a n g e f r o m 10- * to 10-Xmm. Hg. C o n t r a r y to s t a t e m e n t s m a d e in p r e v i o u s p u b l i c a t i o n s t h e c u r v e s do n o t s h o w linear relationship b e t w e e n voltage a n d pressure in t h e r a n g e u p to 0.1ram. Hg. F i n a l l y t h e a u t h o r s c o m p a r e v a l u e s for t h e m a n o m e t r i c c o n s t a n t proposed b y V o n U b i s c h w i t h t h o s e b a s e d on t h e i r o w n e x p e r i m e n t a l results w h i c h d e v i a t e a p p r e c i a b l y f r o m t h e former. Sommaire : R e v u e des c o n n a i s s a n c e s actuelles de la j a u g e Pirani, et d6tails s u r certaines experiences c o n d u i t e s p a r les a u t e u r s s u r les caract6ristiques de la jauge.

Article by G. Glockler & H. V. Hor~t Science xx6, Oct. 1952 364-367 13/II

Heat Conductivity of Gases at Low P r e s s u r e s See A b s t r a c t No. : 4 / I V Stabilised Ion Gauge Control U n i t Canada. T h e description a n d circuit d i a g r a m of a control u n i t is g i v e n w h i c h is similar to t h e one available f r o m Distillation P r o d u c t s (type HG-200), b u t w h i c h c a n be f a b r i c a t e d f r o m readily available c o m p o n e n t s . I t consists m a i n l y of a stabilised p o w e r s u p p l y to provide t h e electrode v o l t a g e s for t h e g a u g e t u b e , a d.c. amplifier for r e a d i n g t h e ion c u r r e n t a n d a control circuit to m a i n t a i n t h e electron c u r r e n t c o n s t a n t . T h e grid v o l t a g e is - 1 2 . 5 a n d t h e g a u g e t u b e c u r r e n t 5 m A . Detailed o p e r a t i n g i n s t r u c t i o n s are g i v e n covering also d e g a s s i n g p r o c e d u r e s a n d t h e d e t e c t i o n of grid a n o d e a n d grid f i l a m e n t leakages. T h e u n i t described is designed for use w i t h t h e V G 1 A g a u g e b u t will s u i t o t h e r t y p e s of ionisation gauges. T h e calibration c u r v e s a n d a p h o t o g r a p h of t h e u n i t are s h o w n . Sommaire: D~tails s u r u n coffret de c o m m a n d e p o u r j a u g e ~t ionisation, p o u v a n t 6tre fabriqud ~ l'aide d'616ments, faciles A se procurer.

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Report by P. A. Redhead N. R.C. Canada Report No. ERB275 Jan. !952

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The Design and Use.of the Electron Diffraction Camera

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United Kingdom. E x a m i n a t i o n b y electron diffraction gives i n f o r m a t i o n o n t h e a r r a n g e m e n t of a t o m s a n d molecules in a m a t e r i a l a n d a t t h e s a m e t i m e a n indication of its crystalline form, b u t its u s e is restricted to t h e s t u d y of surface layers of b u l k m a t e r i a l s or v e r y t h i n films. T h e p l a n t required for t h i s work, a n electron diffraction ~ a m e r a , consists of a c h a m b e r , w h i c h is p u m p e d d o w n to 10-~mm. H g p r e s s u r e a n d c o n t a i n s a n electron g u n m a d e f r o m t u n g s t e n wire. T h e electron g u n is joined to t h e s p e c i m e n c h a m b e r b y a t u b e s o m e 50 cm. long. I n order to e n s u r e t h a t a n electron b e a m of suitable s t r e n g t h is t r a v e l l i n g a l o n g t h e a x i s of

January, 1953

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