AERONOMICA ACTA

Texte intégral

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I N S T I T U T D A E R O N O M I E S P A T I A L E D E B E L G I Q U E 3 - Avenue Circulaire

B - 1180 BRUXELLES

A E R O N O M I C A A C T A

A - N° 277 - 1984

Microprocessor based data acquisition and control system for a balloon borne quadrupole mass

spectrometer

by

D. NEVE JANS, P. FREDERICK and E. ARIJS

V O O R R U I M T E - A E R O N O M I E B E L G I S C H I N S T I T U U T

3 - Ringlaan B - 1180 BRUSSEL

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FOREWORD

The paper "Microprocessor based data acquisition and control system for a balloon borne quadrupole mass spectrometer" will be published in the Bulletin de la Classe des Sciences de l'Académie Royale de Belgique.

AVANT-PROPOS

L'article : "Microprocessor based data acquisition and control system for a balloon borne quadrupole mass spectrometer" sera publié dans le Bulletin de la Classe des Sciences de l'Académie Royale de Belgique.

VOORWOORD

De tekst "Microprocessor based data acquisition and control system for a balloon borne quadrupole mass spectrometer" zal verschijnen in de Bulletin de la Classe des Sciences de l'Académie Royale de Belgique.

VORWORT

Die Arbeit : "Microprocessor based data acquisition and control system for a balloon borne quadrupole mass spectrometer" wird in der Bulletin de la Classe des Sciences de l'Académie Royale de Belgique herausgegeben werden.

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M I C R O P R O C E S S O R B A S E D D A T A A C Q U I S I T I O N A N D C O N T R O L S Y S T E M F O R A B A L L O O N B O R N E Q U A D R U P O L E M A S S

S P E C T R O M E T E R

b y

D . N E V E J A N S , P. F R E D E R I C K a n d E. A R I J S

A b s t r a c t

A m i c r o p r o c e s s o r based data acquisition a n d control s y s t e m h a s been d e s i g n e d and c o n s t r u c t e d for use in balloon b o r n e q u a d r u p o l e mass spectrometers. It combines the capabilities of an ion c o u n t e r / d i s c r i m i n a t o r , a spectrum accumulator, an intelligent mass s c a n c o n t r o l - ler, a multiplexed analog to digital c o n v e r t e r , a relay controller, a P C M encoder for serial digital o u t p u t , multiple analog o u t p u t s a n d an i n t e r - face to remote control s i g n a l s . T h e s y s t e m h a s been flown s u c c e s s f u l l y in the s t r a t o s p h e r e .

Résumé

U n système basé s u r m i c r o p r o c e s s e u r p o u r l'acquisition et le c o n - trôle de d o n n é e s , a été d é s i g n é et c o n s t r u i t p o u r être utilisé d a n s les spectromètres de masse q u a d r u p o l a i r e s portés par ballons. Le système n o u s offre toutes les possibilités d ' u n c o m p t e u r - d i s c r i m i n a t e u r d ' i o n s , u n accumulateur de s p e c t r e , u n contrôleur a n a l y s e u r de masse intelligent, un c o n v e r t i s s e u r analogique - numérique à m u l t i p l e x e u r , u n contrôleur de relais, u n codeur P C M p o u r sortie digitale en série, des sorties analogiques multiples et une interface p o u r s i g n a u x de télé- commande. Le système a volé d a n s la s t r a t o s p h è r e avec s u c c è s .

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S a m e n v a t t i n g

Een op m i c r o p r o c e s s o r g e b a s e e r d systeem voor het verzamelen en het c o n t r o l e r e n v a n g e g e v e n s , w e r d o n t w o r p e n en g e b o u w d om g e b r u i k t te w o r d e n in q u a d r u p o o l massaspectrometers aan b o o r d v a n s t r a t o s f e - r i s c h e b a l l o n s . H i e r i n v e r v u l l e n alle elementen een s p e c i f i e k e rol : een i o n e n t e l l e r - d i s c r i m i n a t o r , een s p e c t r u m a c c u m u l a t o r , een i n t e l l i g e n t e massa " s c a n c o n t r o l l e r " , een analoog - digitaalomzetter met m u l t i p l e x e r , een r e l a i s c o n t r o l l e r , een P C M e n c o d e r voor d i g i t a l e s e r i e - u i t v o e r , meer- v o u d i g e analoge u i t g a n g e n en een " i n t e r f a c e " v o o r telecommando- s i g n a l e n . Het systeem maakte s u c c e s v o l l e v l u c h t e n in de s t r a t o s f e e r .

Zusammenfassung

Ein M i k r o p r o z e s s o r b a s i e r t e n System um Daten zu e r w e r b e n u n d zu k o n t r o l l i e r e n w u r d e e n t w o r p e n u n d e n t w i c k e l t um in q u a d r u p o l a r e n M a s s e n s p e k t r o m e t e r n , e i n g e b a u t in B a l l o n e n , g e b r a u c h t zu w e r d e n . Folgende Elementen haben eine s p e z i f i s c h e Rolle zu spielen : ein l o n e n - z ä h l e r / D i s k r i m i n a t o r , ein S p e k t r u m a k k u m u l a t o r , ein i n t e l l i g e n t e r Massa - A b s t a s t e r , ein A n a l o g - Digital - Wandler mit M u l t i p l e x e r , ein R e l a i s - r e g l e r , ein P C M V e r s c h l ü s s l e r f ü r Digital - S e r i e n a ü s g a b e , m e h r f a c h e n A n a l o g a u s g a b e n u n d eine S c h n i t t s t e l l e f ü r f e r n e K o n t r o l l e s i g n a l e n . Das System w u r d e e r f o l g r e i c h in d e r S t r a t o s p h ä r e g e f l u g e n .

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1. I N T R O D U C T I O N

Recently there h a s been a g r o w i n g interest in the m e a s u r i n g a n d modelling of the positive and negative ion composition of the s t r a t o - s p h e r e , p a r t i c u l a r l y as a p r o m i s i n g new method for the detection of trace g a s e s with v e r y low concentrations ( 1 - 3 ) .

T h e r e f o r e balloon borne mass spectrometers h a v e been built b y these a u t h o r s ( 4 ) a n d o t h e r s ( 5 , 6 ) . S u c h an i n s t r u m e n t mainly c o n s i s t s of a h i g h speed c r y o g e n i c pump ( 7 ) , a sampling hole, a q u a d r u p o l e mass filter operated in h i g h v a c u u m and the associated electronics. T h e s t r a t o s p h e r i c ions are sampled t h r o u g h the small hole and are f o c u s s e d into the mass filter, where t h e y are selected a c c o r d i n g to their mass to c h a r g e ratio. N e u t r a l s are pumped b y the h i g h speed p u m p . A f t e r p a s s i n g the q u a d r u p o l e ions reach a h i g h gain electron multiplier w o r k i n g in the p u l s e c o u n t i n g mode. T h e c h a r g e p u l s e s at the anode of the multiplier are discriminated and counted d u r i n g a time window. T h e c o r r e s p o n d i n g number of detected ions is then classified within a mass s p e c t r u m .

For application in s u c h i n s t r u m e n t s o u r g r o u p c o n s t r u c t e d a p r o - grammable controller ( 8 ) which combined a fast 24-bit ion c o u n t e r and a remotely controllable mass selection unit. With this controller a n d a mass filter h a v i n g a mass r a n g e upto 110 amu the f i r s t mass s p e c t r a of the positive s t r a t o s p h e r i c ions, obtained b y a balloon b o r n e i n s t r u m e n t , h a v e been measured ( 9 ) . In o r d e r to improve the performance of the balloon borne mass spectrometer a new o n - b o a r d data management s y s t e m has been d e s i g n e d based u p o n c u r r e n t 8 - b i t m i c r o p r o c e s s o r t e c h n o l o g y . Its premium t a s k was the storage and integration of mass s p e c t r a , but we took also benifit of its computing and control power to u p g r a d e other f u n c t i o n s of the i n s t r u m e n t .

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It is the aim of this paper to describe the technical details of the new system, which are applicable to many other balloon-borne or remotely controlled experiments.

2. R E V I E W O F M A S S S C A N N I N G T H E O R Y

O u r s t r a t o s p h e r i c • mass spectrometer uses an electrical q u a d r u p o l e as a mass filter/ the theory of which is well established. Paul et al ( 1 0 ) showed that in the field of a q u a d r u p o l e , supplied with D C voltages U and - U and R F voltages V . c o s u> t and - V . c o s u> t and h a v i n g a field o o r a d i u s r , the motion of a c h a r g e d particle with mass m and c h a r g e e is g o v e r n e d b y Mathieu differential equations of the form :

— + (a - 2.q .cos 24).x = 0 ,2 2 x x

where

2

^ + (a - 2.0 .cos 2 | ) . y = 0

8.e.U

a = - a - a - 2 Z

x y m.(J . r

x y m. to .r

o o 2.4 = U) t * o

B o u n d e d solutions for these equations only exist when a and q are pointing to a spot within a stability zone in the (a, q ) plane. T h e contours of this area can be approximated b y the c u r v e s (see f i g u r e 1)

^ 1 2 7 4 .29 6

a(q) = 2 • q 128 ' + 2 3 0 4 " q

, , 1 2 1 3 1 4 a(q) = 1 - q - 8 -q + 64 • q - 1536 • q +

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In practice, the applied D C a n d R F v o l t a g e s U a n d V . c o s u)Qt are related, so that : U = U ( V ) . If we limit o u r s e l v e s then to the filtering of a specific ion with mass m a n d c h a r g e e, stable solutions e x i s t o n l y for ( a , q ) points located within the stability zone a n d on a c u r v e :

. ( » ) - 2. S f l l . „

If we a r r a n g e a linear relationship between U and V the c u r v e a ( q ) becomes a s t r a i g h t line and c r o s s e s the stability diagram at the tip (a^

= 0,237; q1 = 0 , 7 0 6 ) ; hence : U(V) = K rV

w i t h

a

K = TT^ 0,16784 1 2q 1

T h e w o r k i n g zone reduces now to a u n i q u e point and the mass of the transmitted ion becomes a linear function of the R F amplitude :

4.e _ v

to o o 1 ? 2

When the R F voltage is modulated b y a linear ramp f u n c t i o n a linear mass v e r s u s time relation will evolve and mass p e a k s with infinite resolution ( i n t h e o r y ) will a p p e a r . If the amplitude V is limited b y the q u a d r u p o l e power s u p p l y to Vm g x, the mass r a n g e e x t e n d s to :

4 . e . V

m max

co 2 .r 2 o ° 1 In the more general case that

U(V) = K.V w i t h o a n

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the w o r k i n g zone e x p a n d s from a point to a linear segment between ( a2, q2) a n d ( a3, q3) ; see f i g u r e 1. If the R F voltage is modulated in a similar way as before, then the trajectories of ions with mass m and c h a r g e e become stable

m.io . r 2 2

from V2 = °e • q2 (q2 < ^

m.(jJ . r 2 2

v3 = °4 e ° • q3 (q3 > V

T h e ions are o b v i o u s l y filtered with a c o n s t a n t , finite resolution ( = because ( V2 + V3) / ( V2 - V3) is i n d e p e n d e n t of m a s s . B y lowering K well below K1 = 0,16784 one can make appear the r i s i n g edge of a g i v e n peak ( m a s s ) at a much lower R F amplitude Ve d g e :

m. w . r 2 2

Vedge = V2 < °4e ° '

T h e r a n g e of detectable masses will then e x p a n d to

ql >

m = m • — > m max,q maXjq^ q^ max,q

while the relation between Ve d g e and mass remains linear.

T h i s technique of " r i s i n g edge detection" offers the p o s s i b i l i t y of e x t e n d i n g the mass r a n g e b e y o n d the R F limited mass r a n g e associated with infinite resolution. It has been applied v e r y s u c c e s s f u l l y b y o u r g r o u p for the measurement of negative s t r a t o s p h e r i c ion a b u n d a n c e s upto 391 a.m. u. ( 1 1 ) . A special case e x i s t s when no D C is applied to the q u a d r u p o l e r o d s ( q2 = 0; q3 = 0 . 9 0 8 ) . T h e q u a d r u p o l e acts then as a h i g h p a s s filter : only masses above 4 e V / ( 0 . 9 0 8 x u»Q . rQ ) are transmitted.

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I/O BOARD SELECT LINES

Q

I/O SERVICE BOARO

CONTROL

I/O BUS

Fig. i.- Stability diagram of the Mathieu differential equations governing the motion of charged particles in an electrical quadrupole (first

region only).

Scanning line for constant resolution : a = 2 Kq a = 8e U/(m u> :2 r 2)

q = 4e V/(m u) . r ) 2 2

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Finally a third method of operation of the mass filter can be imagined in which the peak-width Am of the mass peaks is a constant.

This condition can be satisfied when operating the mass filter close to the tip of the stability diagram and when we make the ratio U/V a non-linear function of V. Near the tip the diagram contours can be linearized so that the intersection points with the curve a ( q ) = 2q.

can be easily found. Paul et al. (10) have calculated that in this case the resolution R is given by :

R = HL_Am 2.K jq^ - aCq-^) n = ° -1 7 8 (q = 0.706)

Since at the tip q2 en q3 are close to q^, we can assume that the mass-RF relation for high resolution still holds :

m - - 2 — • V

Uo -ro -qi

If then Am has to remain undependent on mass, we find the following relations :

a ( q i) = 2 K i q i- 0 . 1 7 8 ^

= 2 • ! " «1

h K1 " K2 * t2 w i t h K2 = ° "1 7 8 " o2 ro2 / 8 e U = K j . V - K2.Am

The constant peak-width ( C P W ) mode can thus be realized either by offsetting the scan line U = K r V by an amount - K2.Am which varies linearly with desired peak-width, or by making the slope of the scan line U = U ( V ) mass dependent.

The latter solution is employed in our instrument for flexibility reasons. The CPW mode produces peaks which are broader at low

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masses (and result in a higher transmission) when compared to the fixed resolution mode if high mass peak-widths are made equal in both modes.

3. D E S I G N O B J E C T I V E S

a) Spectra management

From previous flights with an earlier version of our stratospheric mass spectrometer we learned the extreme importance of a v e r y flexible communication link between the g r o u n d - b o r n e experimenter and the balloon-borne instrument. In this mass spectrometer the observed ion count rates were not stored on-board but instead directly t r a n s - mitted by telemetry as a pulse code modulated ( P C M ) digital data stream.

T h i s involved that storage of mass spectra and their integration over long time periods was done on g r o u n d , so that every disturbance in the telemetry link or in the data handling system could severely spoil the measurements. Furthermore the data transmission format, which was solely based upon the use of digital ( P C M ) data, implicated that real- time interpretation of spectra was impossible without a computer.

Therefore it was decided to move the spectrum storage function to the other end of the telemetry link, i.e. to the instrument. T h i s imple- mentation made it possible to let the mass spectrometer produce simul-

j

taneously on-board slow analog, paper recorder compatible, -spectrum output as well as computer compatible, serial PCM spectrum data. So, even when no real-time PCM treatment is done or can be done, the experimenter will still have access to real-time copies of the currently observed ion mass spectrum. The analog copy is made available on 3 analog telemetry channels, each with a different, software selectable scale factor. Spectrum excursions become thus adaptable to signal

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a b u n d a n c e . T h e 3 analog s p e c t r u m o u t p u t s can also be r e c o n f i g u r e d b y software, u n d e r remote control, so that s e q u e n c e rotation of these 3 telemetry c h a n n e l s r e s u l t s . T h i s feature helps to c i r c u m v e n t failure of a s i n g l e telemetry c h a n n e l .

b ) M a s s s c a n n i n g

A main objective of a s t r a t o s p h e r i c mass spectrometer f l i g h t is to measure the relative a b u n d a n c e s of the different ion species at d i f f e r e n t altitudes a n d to deduce from this concentration profiles of trace g a s e s ( s u c h as : H20 , C H3C N , N a O H , HNC>3, H2S 04, e t c . ) i n f l u e n c i n g the positive or negative ambient ion composition. T h e s t r a t o s p h e r i c ions are

o _ o

few a b u n d a n t ( a p p r o x . 10 cm ), so that a considerable amount of flight time is consumed for b u i l d i n g up a single s p e c t r u m . In practice t h e r e f o r e , we t r y to make a v e r y efficient signal u s a g e t a k i n g into account both time consumption and d e s i r e d information.

C o n s i d e r a b l e time can be g a i n e d b y selecting an a p p r o p r i a t e mass s c a n n i n g mode. In o u r new m i c r o p r o c e s s o r controlled i n s t r u m e n t we h a v e the p o s s i b i l i t y to select the following s c a n parameters b y software backed remote control : 1) resolution mode 2) extend of the scan r a n g e 3) number of s p e c t r u m c h a n n e l s 4) total scan time. T w o resolution modes are implemented. I n - t h e f i r s t mode the resolution is held c o n s t a n t all o v e r the mass r a n g e , r e s u l t i n g in a linear relationship between p e a k - w i d t h and mass number (see p r e v i o u s s e c t i o n ) . T h i s mode is primarely u s e d in cases where the mass n u m b e r s of the ions are k n o w n beforehand and one only wants to measure relative a b u n d a n c e s of these ions. A v e r y coarse resolution can be used together with the " r i s i n g edge detection" technique . T h i s r e s u l t s in a h i g h q u a d r u p o l e t r a n s - mission and c o n s e q u e n t l y a faster s p e c t r u m b u i l t - u p . In the c o n s t a n t p e a k - w i d t h mode the resolution is made a linear function of mass. It is u s e d f o r the u n a m b i g u o u s determination of ion mass n u m b e r s b y i n - f l i g h t calibration because mass p e a k s can be resolved equally well all o v e r the mass r a n g e .

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T h e R F s c a n r a n g e is the second parameter we can modify to optimize o u r measurement t e c h n i q u e . In o u r s y s t e m a choice can be made between the full scan r a n g e a n d a n u m b e r of medium and small sized s c a n r a n g e s . Each scan r a n g e is related to a mass n u m b e r r a n g e , the extend of which d e p e n d s u p o n the selected peak resolution a n d the criterion u s e d for ion identification (either peak or r i s i n g e d g e ) . T h e full mass r a n g e is u s e d primarely for a coarse resolution f i r s t look at the ion mass d i s t r i b u t i o n . O b v i o u s l y the small sized mass r a n g e s h a v e been i n t r o d u c e d to yield a reduction in s c a n time. T h e y e x t e n d o n l y o v e r a few ( 1 0 ) a . m . u . and are employed, mostly in a c o n s t a n t p e a k - width mode, to enhance the s i g n a l - t o - b a c k g r o u n d ratio in p a r t s of the

i

s p e c t r u m where interesting f e a t u r e s are expected. S u c h f e a t u r e s are : isotopically related p e a k s , v e r y small p e a k s , etc. T h e medium sized mass r a n g e s compromise between r a n g e s p a n (bb a . m . u ) a n d scan time.

T h e y are d i s t r i b u t e d o v e r the full mass r a n g e so as to c o v e r an optimum number of mass p e a k s usable for mass scale calibration. T h e i r main application is in the determination of u n k n o w n ion mass n u m b e r s .

T h e next scan parameter we can optimize is the n u m b e r of s p e c t r u m c h a n n e l s . Its value is v a r i e d in function of resolution : s c a n s p r o d u c i n g wide flat-topped p e a k s are always performed at approximately 2 c h a n n e l s per a . m . u . , while fine resolution s p e c t r a demand f o r 6 c h a n n e l s per a . m . u . . Total scan time does not affect efficiency. It is equal to the p r o d u c t of the number of c h a n n e l s and the c o u n t i n g window time per channel and is determined b y two f a c t o r s . T h e s c a n repetition rate must be fast e n o u g h to show s h o r t - t e r m ion population v a r i a t i o n s and on the other h a n d , it must be slow e n o u g h to s t a y in pace with the t r a n s m i s s i o n of analog s p e c t r u m copies. T h e r e f o r e a d u r a t i o n of 250 msec has been a s s i g n e d to the window.

c ) O t h e r control f u n c t i o n s

T h e principal t a s k s of the d e s c r i b e d s y s t e m are the management of spectra and the mass s c a n n i n g p r o c e d u r e . B e s i d e s that however some

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other duties are performed b y the m i c r o p r o c e s s o r without interference with the mass s c a n n i n g , analog spectra t r a n s m i s s i o n or P C M g e n e r a t i o n . A v e r y important job executed b y the m i c r o p r o c e s s o r is the remote control p r o c e d u r e . It c h e c k s the received remote control code for validity and reacts on it with the execution of s e r v i c e p r o g r a m s or s c a n definition p r o g r a m s . T h e latter p r o g r a m s are u s e d to define f u t u r e mass s c a n s . T h e y r u n totally c o n c u r r e n t with the p r e s e n t mass s c a n in o r d e r to s a v e measurement time. T h e s e r v i c e p r o g r a m s take care of the following f u n c t i o n s : fine or coarse incrementing or decrementing of the d r a w - i n potential at the sampling hole, polarity s w i t c h i n g between positive or negative ions, s w i t c h i n g between ion sampling mode and neutral (ion s o u r c e ) mode, o p e n i n g of the protective cap of the mass spectrometer, rotation of telemetry c h a n n e l s and selecting of s p e c t r u m scale factors (see section 3 . a ) . A g a i n t h e y r u n totally t r a n s p a r e n t to the principal t a s k s of the m i c r o p r o c e s s o r .

4. H A R D W A R E I M P L E M E N T A T I O N

F i g u r e 2 s h o w s a block diagram of o u r b a l l o o n - b o r n e micro- p r o c e s s o r based data acquisition and control s y s t e m . T h e heart of t h i s s y s t e m is formed b y 3 b o a r d s which are interconnected b y a s y s t e m b u s c o n s i s t i n g of a data b u s (8 b i t s ) , an a d d r e s s b u s (16 b i t s ) a n d a control b u s ( M E M R , MEMW, I N T A , i n t e r r u p t ) . T h e s e b o a r d s are : a m i c r o p r o c e s s o r b o a r d , a memory board a n d an i n p u t / o u t p u t ( I / O ) s e r v i c e b o a r d . T h e m i c r o p r o c e s s o r board contains an 8 - b i t micro- p r o c e s s o r (Intel M 8 0 8 0 A ) and its associated clock g e n e r a t o r (M8224) and b u s control circuits ( M 8 2 2 8 ) . T h e m i c r o p r o c e s s o r executes i n s t r u c t i o n s fetched from the memory board which p a c k s a p r o g r a m a n d a w o r k area. P r o g r a m s are stored in erasable reprogrammable read o n l y memories (Intel M2716, 2K b y t e s e a c h ) so that p r o g r a m loading from a mass storage device is not r e q u i r e d .

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START ON TERMINAL COUNT

J

I COU*

t l _

«-COUNT H«-«!

' WINDOW ' FROM PULSE BUFFER

TÎT±>Ml

J n X L M 1 6 0

PROGRAMMABLE INTERVAL TIMER M8253

INTERRUPT

MEMW LOWER SELECT

LINE

Fig. 2.- Block diagram of the balloon borne, microprocessor based data acquisition and control system.

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T h e w o r k area is constituted of static random access memories ( M o s t e k M K B 4118, 1K b y t e s each) a n d s t o r e s p r o g r a m s t a c k , p r o g r a m v a r i a b l e s , alterable i n s t r u c t i o n s , mass s p e c t r a , P C M frames, s c a n p a r a - meters, etc. T h i s memory b o a r d has been d e s i g n e d for E P R O M / R A M i n t e r c h a n g e b i l i t y and can be r e c o n f i g u r e d for u p g r a d i n g to f u t u r e software needs. C u r r e n t l y memory space can be defined as a n y combina- tion of 2N K E P R O M memory + (6 - N ) K R A M memory with N = 1 to 5.

T h e t h i r d b o a r d connected to the s y s t e m b u s is the i n p u t / o u t p u t s e r v i c e b o a r d . It f u n c t i o n s as a link between the other s y s t e m b o a r d s and the I/O interface b o a r d s d e s c r i b e d hereafter. O n t h i s b o a r d the i n t e r r u p t controller (Intel M8259) is located. It h a n d l e s i n t e r r u p t r e q u e s t s from the I/O b o a r d s and is programmed b y the m i c r o p r o c e s s o r software to w o r k in the nested mode, i.e. r e q u e s t s are o r d e r e d in p r i o r i t y . In o r d e r to reduce local a d d r e s s d e c o d i n g requirements on the I/O b o a r d s the same board is also e q u i p p e d with an I/O a d d r e s s decoder which p r o d u c e s I/O board select s t r o b e s ( 2 per b o a r d ) . T h e a d d r e s s e s of the b o a r d s are memory mapped so that no specific I/O i n s t r u c t i o n s are r e q u i r e d for i n p u t / o u t p u t .

T h e I/O interface b o a r d s are interconnected b y an I/O b u s a n d communicate with the outside world : the q u a d r u p o l e s u p p l y , the ion detector, telemetry, remote control and a set of r e l a y s . T h e I/O b u s is constituted of the system data b u s (8 b i t s ) , the s y s t e m control b u s , a r e d u c e d a d d r e s s b u s ( A and A ^ ) and an i n t e r r u p t b u s (8 lines, w i r e d - o r a b l e ) . In the c u r r e n t h a r d w a r e implementation the following interface b o a r d s are installed : 1) an ion counter/discriminator board 2) a mass filter control board 3) a parallel and serial digital I/O b o a r d 4) an analog o u t p u t board 5) a multiplexed analog data acquisition b o a r d .

T h e ion counter/discriminator ( f i g u r e 3) receives negative p u l s e s from an ultra fast pulse b u f f e r ( N S L H 0 0 3 3 ) connected to the anode of the ion detector (a Galileo S p i r a l t r o n t y p e 4219). T h e s e p u l s e s are checked b y a pulse h e i g h t discriminator ( N S LM160, h i g h speed com-

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SELECT L I N E

F i g . 3.- Ion counter discriminator b o a r d . Counting window :

• 1 (•>

1 to 2 -1 m s e c ; number of ions counted : m a x .

21 6- 1 .

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(18)

p a r a t o r ) a n d are s u b s e q u e n t l y counted b y a programmable interval timer (Intel M8253). T h e latter c i r c u i t is o r g a n i z e d as three i n d e p e n d e n t 16-bit c o u n t e r s , programmable b y software to perform in a specific mode of operation. C o u n t e r O is c o n f i g u r e d as an event c o u n t e r (mode O ) and c o u n t s the number of ion p u l s e s received d u r i n g a c o u n t i n g window. T h e window pulse d u r a t i o n is determined b y c o u n t e r 1 acting as a programmable o n e - s h o t (mode 1 ) , while the t h i r d counter is programmed as a f r e q u e n c y d i v i d e r (mode 2) p r o d u c i n g a 1 K H z clock rate. C o n s e q u e n t l y , ions can be counted d u r i n g c o u n t i n g w i n d o w s r a n g i n g from 1 msec upto 2 - 1 msec or more t h a n 1 minute. Additional 16 c i r c u i t s are r e q u i r e d to make the event counter b e h a v e p r o p e r l y . F i r s t

16

of all, when the latter reaches terminal count (2 - 1 ) the c o u n t i n g p r o c e d u r e must be stopped b y g a t i n g off the window pulse in o r d e r to p r e v e n t misleading r e s u l t s . A l s o when no p u l s e s at all h a v e a r r i v e d d u r i n g a window pulse the ion counter c o n t e n t s , as a c q u i r e d b y the m i c r o p r o c e s s o r read i n s t r u c t i o n s , may look e r r o n e o u s . T h e s e 2 conditions - terminal count and empty counter - are therefore detected b y 2 flag f l i p - f l o p s and made accessable for r e a d - o u t b y the counter software routine.

T h e mass filter control b o a r d ( f i g u r e 4) masters the mass and resolution setting of the q u a d r u p o l e mass filter. It g e n e r a t e s 2 v o l t a g e s V and a . V which are used to control the q u a d r u p o l e power s u p p l y ,

c c

Digital information c o n c e r n i n g Vc and a is sent b y the m i c r o p r o c e s s o r via a programmable peripheral interface (Intel M8255). P o r t s are com- bined to form digital i n p u t s to a 12-bit d i g i t a l - t o - a n a l o g ( D A C ) c o n - v e r t e r and a 12-bit multiplying D A C ( M D A C ) . T h e R F o u t p u t of the q u a d r u p o l e s u p p l y is made linearly proportional to the D A C o u t p u t Vc, which can take 4096 v a l u e s between 0 and 9,9976 Volts ( V = P - Vc) . T h e M D A C f u n c t i o n s as a digital potentiometer a n d g o v e r n s the slope of the s c a n n i n g line a = 2 q . U / V in the stability diagram of the q u a d r u p o l e (see section 2 ) . A combination of its o u t p u t a . Vc and the D A C o u t p u t V d r i v e s the D C section of the q u a d r u p o l e s u p p l y , the o u t p u t of which is g i v e n b y : c

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F i g . 4.- M a s s f i l t e r c o n t r o l b o a r d a n d its c o n n e c t i o n to the q u a d r u p o l e s u p p l y . G is c h o o s e n e q u a l to p . K - 1 for c o n v e n i e n c e .

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U = I K . + G.U f i n e coarse

D e p e n d i n g u p o n the position of a software controlled switch in the q u a d r u p o l e power s u p p l y either a coarse or a fine resolution mode can

be selected. In the f i r s t mode U a n d I L . are both equal to coarse fine ^ a . V . so that :

c '

U/V = (1+G).a/0

or

0 ^ ^ g w i t h 0 g a g a = 0,99976 V 0 max

If now G is made equal to p.K.^-1 the s c a n n i n g line can be g i v e n a n y slope between the h i g h p a s s mode ( D C = 0 ) a n d infinite resolution.

When the fine mode is called on we get

U = V coarse c

= a.V

f i n e c

G/B U/V ^(G + a )/p

v max

or

K j - 1/0 ^ U/V S K1

T h e slope of the s c a n n i n g line (= 2 U / V ) can t h u s be v a r i e d at will o v e r 4096 positions in a restricted r a n g e near the apex of the stability d i a g r a m . In the case we hold a constant while Vc is being sweeped, spectra will appear with a constant fine resolution g i v e n b y :

0.178 0.126 R = 2 K q i- a ( q i) K ^ - U/V

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or

0.126 p ^ R ^ °°

!

We can also a r r a n g e for constant p e a k - w i d t h s p e c t r a . T h e condition for c o n s t a n t p e a k - w i d t h Am is :

U „ Am V 1 2 ' V

T h e r e f o r e the following relation must exist between the digital codes sent to the D A C (= V ) and to the M D A C (= a ) :

a = y - 6/Vc

w i t h

y = Krp - G = 1

ô = K2.Am

T h i s relationship has been implemented b y a software routine calculating a ( Vc) with y a n d 6 as parameter i n p u t . Its application implies a lower mass limit : V must be at least equal to 6 to yield positive a v a l u e s ,

c

T h e same software routine computing a ( Vc) = y - ô / Vc can be u s e d for all resolution modes when y and ô are generalized as in table I.

A s mentioned before copies of spectra stored in the m i c r o p r o c e s s o r R A M memory are sent to the r e c e i v i n g station in a serial P C M format.

T h e circuit which is r e s p o n s i b l e for the c o n v e r s i o n p r o c e s s of b y t e - w i d e b i n a r y information to a serial bit stream is a programmable communica- tion interface (Intel M8251). It is part of the parallel a n d serial I/O board s h o w n in f i g u r e 5. For o u r application it is c o n f i g u r e d b y s o f t - ware to w o r k e x c l u s i v e l y as a s y n c h r o n o u s transmitter. T h e data at its o u t p u t a p p e a r s therefore as a c o n t i n u o u s N R Z - L ( n o - r e t u r n - t o - z e r o

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TABLE 1.- a = Y - ô/V

Mode

fine

fine a.V

coarse a.V

U coarse Y Ô Resolution

1 V < 1

c

1

0 0 high pass a.V < 1 0 coarse

0 infinite 0 finite K-Am constant Am

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X

| PRESET: POINTERS, BUFFERS & PARAMETERS

1

I —;

I DEFINE I/O BOAROS I I SWITCH TO REMOTE CONTROL I 1 ' I

| ENABLE INTERRUPTS & START P C M ] (MAIN-LOOP^)

I

NON-VALID

I ARM_ RC I

VALID. BUT DISARMS

VALID ft ARMEO

RC • REMOTE CONTROL

I DISARM RCl

i

USERCCOOE AS INDEX IN LINKTABLEjGET MOOE

BUSY

F11TIIRF STAN

BUSY

DEFINITION

SAVE RC CODE IN SCAN-COOE

CONCURRENT SERVICE PROGRAM

JUMP TO SERVICE PROGRAM VIA

DONE

sm

LINKTABLE

USE SAVED SCAN- CODE AS INDEX IN

LINKTABLE JUMP TO SELECTED X

SCAN ROUTINE VIA LINKTABLE

FILL PCM RAM BUFFERS WITH:

-SCAN PARAMETERS - SPECTRUM - TECHNOL. DATA

I LOOP BACK

MAIN PROGRAM LOOP INTERRUPTED BY SCAN ROUTINES ft PCM ROUTINE

. 5.- Parallel and serial I/O board.

Upper part : serial I/O : PCM output.

Lower part : parallel I/O : remote control input and relay control output.

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level) encoded serial data stream without a n y a d d e d s t a r t , stop or p a r i t y bits. T h e N R Z - L data are f u r t h e r c o n v e r t e d b y a C M O S encoder ( R C A C D 4 0 3 7 ) into a b i - p h a s e level (bi-<|>-L) s i g n a l , which is an adequate c o d i n g scheme for P C M data. T h e bit rate of the r e s u l t i n g bi-<t> signal is determined b y a b a u d rate g e n e r a t o r c o n s i s t i n g of a c r y s t a l oscillator a n d a tapped f r e q u e n c y d i v i d e r c i r c u i t . In the p r e s e n t c o n f i g u r a t i o n serial data are transmitted at about 800 bits/sec o v e r an I R I G s t a n d a r d channel E ( 2 . 1 K Hz b a n d w i d t h ) . T h e limiting factors for the choice of the b a u d rate are the maximum allowed b a u d rate for the M8251 (56 K b a u d ) a n d the time s p e n t in the P C M i n t e r r u p t routine d e s c r i b e d f u r t h e r . O n the same I/O interface b o a r d parallel I/O c i r c u i t r y is i n c o r p o r a t e d . It c o n s i s t s in a programmable peripheral interface (Intel M8255), the 24 I/O lines of which are accessible at 3 b y t e - w i d e p o r t s A , B a n d C . T h e functional c h a r a c t e r i s t i c s of the p o r t s can be defined b y software. In o u r application port A is c o n f i g u r e d as a n o n l a t c h i n g i n p u t p o r t r e c e i v i n g an 8 - b i t remote control code d e - livered b y telecommand. Port C is programmed as an 8 - b i t data latch h a v i n g a s i n g l e bit set/reset feature. It controls a b a n k of r e l a y s , each s w i t c h i n g or activating one of the following items : the polarity of the ion f o c u s s i n g v o l t a g e s , the polarity and absolute value o f the ion detector cone voltage, the ion lens mode (ion s o u r c e or natural ion sampling)., the q u a d r u p o l e s u p p l y mode (fine or c o a r s e ) , v a l v e positions (atmospheric or calibration g a s ) and the ignition of cable c u t t e r s ( o p e n i n g of the v a c u u m s y s t e m ) . T h e t h i r d port B is r e s e r v e d for f u t u r e e x p a n s i o n of the remote control code.

T h e analog o u t p u t board ( f i g u r e 6) has a v e r y compact c o n f i g u r a - tion. It c o n s i s t s simply of six 8 - b i t monolithic D A C s ( S i g n e t i c s S E 5 0 1 8 ) , each with a reference s o u r c e , an o u t p u t amplifier a n d a data latch incorporated. A n a d d r e s s decoder circuit ( 5 4 L S 1 3 9 ) p r o d u c e s latch enable p u l s e s , one for each of the six D A C s . T h e s e p u l s e s are u s e d to extract data from the data b u s . F o u r of the D A C o u t p u t s are connected to the telemetry package b y long w i r e s . T h e y are b u f f e r e d b y a voltage

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(SAMPLE-SMALL-W)

POSITIVE IONS(PI.)

[SET LENS VOLTAGES TO NEGATIVE

POLARITY

NEGATIVE IQNSIN I.)

|SEND INITIAL RF VALUE TO PAC ~|

^ r r o N f

I SET LENS VOLTAGES TO POSITIVE

POLARITY T

CALCULATE INITIAL a ( V c ) , SEND a TO MOAC

I OEM FOR NEGATIVE IONS

SEND CURRENT DRAW-IN & I

ION ENERGY VALUE TO ANALOG OUTPUT BOARP

CALCULATE NEXT SET : I

Vc . AVc & a ( V c . AVc) SELECT DRAW-IN

VOLTAGE FOR R I. SELECT DRAW-IN

VOLTAGE FOR N.I. CONFIGURE LEVEL • INTERRUPT LOCATION:3MP INTERRUPT-SCAN

I SWITCH QUAD SUPPLY TO FINE RESOLUTION*

PCOMTOSE SCAN PARAMETERS |

NO POLARITY CHANGE

I START ION COUNTER | _ L ' 1

| CLEAR ANALOG SPECTRUM OUTPUTS!

KSCAN-STATUS » BUSY |

A «

ENTRY ON ION COUNTER INTERRUPT ' CLEAR STORED _

SPECTRUM. DECLARE:

NEXT SPECTRUM IS FIRST OF NEW SERIES

!<JHTÏRRUPT-SC«£

n r , ISAVE >1P REGISTERS ]

Ï

HO STOP

A L=5jCALL STAOT-SCAN

C R E T L

3

SCAN STOP OEMAHCED

FFTJSE TIME ELAPSED

• - ,

IREAD ION COUNT I

(SCAN- STATUS)«

NOT BUSY

TSCAN PAUSE ACTIVE

SEND NEXT Vc & a

TO DAC & MOAC GENERATE CALIBRATION RBTTERN

4 *

[|NCREMENT#STEPS| START ION COUNTER

CLEAR ANALOG . SPECTRUM OUTPUTS

AT SPECTRUM END IOGMAND SPECTRUM STOPI

I START ION COUNTER) A00 COUNT TO CURRENT SPECTRUM CHANNEL CONTENTS CONVERT ACCUMULATED OOUNT TO ANA-1 LOG OUTPUT WITH 3 SCALE FACTORS I CALCULATE ECXT SET: Vc. A\fc)| X

' 1

D E C L A R E L E V E L 9 S E R V I C E D

RESTORE >1P Z

REGISTERS X

E N A B L E INTERRUPTS |

: R E T

BACK TO INTERRUPTED PROGRAM

F i g . 6.- Analog output board. Six 8-bit digital-to-analog converters giving spectrum output, a time- multiplexed signal and control voltages.

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follower (LM 148) to prevent instabilities due to capacitive loading.

T h r e e of these DACs deliver analog copies of the stored mass spectrum with an 8-bit resolution and a different scale factor. T h e fourth buffered output carries a time - multiplexed signal, composed by the microprocessor's software and showing technological data measured by the multiplexed analog data acquisition board. T h e two non buffered DACs are wired to respond to offset binary code and are used to control the potential of the sampling flange and the ion e n e r g y , in both polarities.

The function of the multiplexed analog data acquisition board represented in figure 7 is to collect samples of important technological data such as : pressure and temperature of the ambient a i r , pressure and temperature inside the instrument, pressure in the mass filter region measured by a Penning gauge, liquid helium levels, the potential of the draw-in flange and the q u a d r u p l e ' s pole bias, ,etc. These data are acquired by a 16 channel 12-bit data acquisition system consisting of merely two functional blocks (Analog Devices AD364 T D ) . T h e f i r s t block forms the analog input section and contains an analog multiplexer, a differential amplifier with high input impedance, a sample-and-hold circuit and switch addressing logic. T h e multiplexer is commanded by software to select a particular input signal either in a single-ended or a differential mode. The sample-and-hold circuit freezes the measured singal value during convertion intervals and is controlled by the second block. T h i s block consists in a 12-bit successive approximation analog- to-digital ( A / D ) converter including 3-state output c i r c u i t r y for con- nection to the data bus. A/D convertions are started by execution of a write instruction to the lower board addresses. After ( t y p i c a l ) 25 (jsec converted data are available as a byte pair on 2 sequential addresses.

5. SOFTWARE

It is obvious that a hardware implementation based upon micro- processor technology must be supported by a powerful software package

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= 1 : READ MODE

7.- Multiplexed analog data acquisition board sampling 16 channels in single-ended or differential mode.

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in o r d e r to take full benefit of the m i c r o p r o c e s s o r ' s capabilities. S i n c e in o u r case we must deal with 2 well timed p r o c e s s e s , namely the mass scan p r o c e s a n d the P C M t r a n s m i s s i o n p r o c e s s an i n t e r r u p t e d software loop s t r u c t u r e has been choosen (see f i g u r e 8 ) .

When power is applied to the s y s t e m , a reset p u l s e , g e n e r a t e d b y the m i c r o p r o c e s s o r b o a r d , is f o r c i n g the p r o g r a m counter to point to the p o w e r - u p section of the main p r o g r a m . In this section the following operations are performed sequentially. F i r s t , the programmable interface c i r c u i t s ( s u c h as M8255, M8251, M8253 a n d M8259) located on the v a r i o u s I/O b o a r d s a n d on the i n t e r r u p t b o a r d are each being p r o - grammed to w o r k in the adequate mode of operation. T h e n p o i n t e r s , status b y t e s , P C M b u f f e r s and the s p e c t r u m area stored in R A M are p r e s e t to their initial v a l u e s . N e x t the P C M i n t e r r u p t routine is initiated which i n v o l v e s that the P C M transmitter is enabled and that a f i r s t i n t e r r u p t from the digital I/O b o a r d may be expected soon.

Finally, the i n t e r r u p t s y s t e m of the m i c r o p r o c e s s o r is enabled.

A f t e r r u n n i n g t h r o u g h the p o w e r - u p section the main p r o g r a m a r r i v e s at the M A I N - L O O P node where a perpetual p r o g r a m loop is started. In this loop several actions are taken : remote control code, scan status a n d s p e c t r u m c o p y s t a t u s are i n t e r p r e t e d , s e r v i c e or s c a n definition routines are p o s s i b l y executed and P C M b u f f e r s are filled.

T h e remote control code, a byte a c q u i r e d via the digital I/O b o a r d , c o n s i s t s of 3 s u b f i e l d s : a 4 - b i t p r o g r a m selection ( P S ) field, a 3 - b i t option field and a 1 - b i t validation field. Remote control ( R C ) codes are being accepted as new on condition that they are recognized as v a l i d , while double acception is avoided b y an arm/disarm mechanism. O n new R C codes the loop b r a n c h e s to a section where it is decided b y table l o o k - u p ( P S field i n d e x e d ) whether a s e r v i c e routine or a s c a n d e - finition routine is called next. S c a n definition routines are s t r a i g h t - f o r w a r d and merely save the c u r r e n t R C code fields for u s e b y the next mass s c a n . S e r v i c e routines however may alter all p r o g r a m p a r a -

(29)

DATA BUS

DATA

n 11

8 - B I T D / A CONVERTERS SE 5018

REFERENCE 4 J VOLTAGE OUT

I N BIPOLAR OFFSET r = SUMMING LE JUNCTION

ANALOG OUT

]

B.O.

S.D.

OUT LE

S.D.

OUT LE

S.D.

OUT LE

c z

S . l OUT LE

a

S . l OUT LE

MEMW

X

• 5V

-r

-5V

-I

•5V QUAD POLE BIAS

CONTROL

OR A W - I N VOLTAGE CONTROL

LM148

ANALOG TIME MULTIPLEX (0 To 2 V )

- H + ANALOG COPIES

OF SPECTRUM ( 0 To 2V)

r r n TT

A' A. l o w e r UPPER L A,

A1 PPT 0 A1

5ALS139

A0 A1 ADDRESS

LOWER UPPER SELECT

LINE

S.D. = SUMMING JUNCTION B P = BIPOLAR OFFSET

F i g . 8.- Simplified flowchart of the main program loop interrupted by the mass scan process and the PCM transmission p r o c e s s .

!

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meters, except those affecting the c u r r e n t mass s c a n . T h e y are u s e d for s u c h simple t a s k s as : i n c r e a s i n g or d e c r e a s i n g the potential of the d r a w - i n plate separately for positive a n d negative ions, c h a n g i n g scale factors of the s p e c t r u m copies, s w i t c h i n g p o l a r i t y , ignition of the u n c o v e r i n g s y s t e m of the sampling hole, e t c . . . If the mentioned test of the R C code fails, the p r o g r a m c h e c k s the mass s c a n s t a t u s . In case the mass s c a n n i n g p r o c e s s is still active the p r o g r a m s k i p s f u r t h e r testing a n d jumps to the P C M b u f f e r filling section ( W O R K - O N - P C M n o d e ) .

O t h e r w i s e an additional check is made to see if the terminated s p e c t r u m is already fully copied b y the P C M routine. If not a jump is made to W O R K - O N - P C M . When s t a t u s information indicates that both mass s c a n n i n g and s p e c t r u m c o p y i n g are done the p r o g r a m selects a new k i n d of s c a n , u s i n g the P S field of a p r e v i o u s l y s a v e d R C code as a pointer ( p o s s i b l e u n c h a n g e d d u r i n g the last s c a n ) . T h e p r o g r a m loop then b r a n c h e s to one of the many s c a n n i n g routines permanently s t o r e d in E P R O M memory. F i g u r e 9 s h o w s the flowchart of a typical s c a n routine p e r f o r m i n g s c a n s with constant p e a k - w i d t h in small mass domains (10 a . m . u . wide) selected b y the s a v e d option field. T h e s e routines all have the same s t r u c t u r e . T h e y f i r s t set up scan parameters t a k i n g into account the option field of the s a v e d R C code. If ion p o l a r i - t y a n d / o r scan parameters differ from those of the p r e v i o u s scan the s p e c t r u m s t o r a g e area in R A M memory is cleared. N e x t , a call is made to a S T A R T - S C A N routine which s t a r t s the mass s c a n p r o c e s s a n d r e t u r n s to the main p r o g r a m loop. T h e latter then continues with the filling of b u f f e r s emptied b y the P C M routine (not d e s c r i b e d in detail) and finally loops back to its b e g i n n i n g .

T h e main p r o g r a m is i n t e r r u p t e d on two occasions : 1) at the end of the c o u n t i n g window of the ion counter 2) when the transmitter of the programmable communication interface (M8251) wants one more b y t e .

In the f i r s t case the i n t e r r u p t controller directs p r o g r a m flow to the

(31)

Fig. 9.- Flowchart of a typical mass scan routine. It calls the START-SCAN routine to begin a scan. The latter continues by interrupt driven calls to the INTERRUPT-SCAN routine.

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I N T E R R U P T - S C A N r o u t i n e , t h e f l o w c h a r t o f w h i c h is d e p i c t e d in f i g u r e 9 . T h i s r o u t i n e r e a d s t h e c o u n t e r c o n t e n t s , a d d s t h e c o u n t t o t h e s p e c t r u m c h a n n e l c o n t e n t s , p r o c e e d s t o t h e n e x t c h a n n e l , s t a r t s t h e c o u n t e r , c o n v e r t s t h e a c c u m u l a t e d c o u n t t o analog o u t p u t a n d r e t u r n s t o t h e i n t e r r u p t e d p r o g r a m s e c t i o n . I n t e r r u p t s a r e d i s c o n t i n u e d w h e n t h e s p e c i f i e d n u m b e r o f s p e c t r u m c h a n n e l s is r e a c h e d . T h e i n t e r r u p t s f o r c e d b y t h e M8251 a r e o f l o w e r p r i o r i t y a n d a r e h a n d l e d b y t h e i n t e r r u p t s e c t i o n o f t h e PCM r o u t i n e . T h e l a t t e r s u p p l i e s t h e M8251 w i t h d a t a f r o m PCM d a t a b u f f e r s f i l l e d in t h e main p r o g r a m loop a n d b e s i d e s t h a t also composes t h e t i m e - m u l t i p l e x e d s i g n a l o u t p u t b y t h e a n a l o g o u t p u t b o a r d .

6 . PERFORMANCE OF T H E SYSTEM

T h e balloon b o r n e mass s p e c t r o m e t e r w i t h t h e new m i c r o p r o c e s s o r based d a t a a c q u i s i t i o n a n d c o n t r o l s y s t e m was f l o w n t w i c e i n 1980. T h e f i r s t b a l l o o n f l i g h t was p e r f o r m e d f r o m t h e CNES l a u n c h i n g base in G a p - T a l l a r d i n S o u t h e r n F r a n c e on 16 J u n e 1980. S p e c t r a w e r e o b t a i n e d f o r p o s i t i v e a n d n e g a t i v e ions i n t h e r i s i n g peak e d g e mode. A n u n - a m b i g u o u s d e t e r m i n a t i o n o f t h e masses of t h e major p o s i t i v e ions at 35 km a l t i t u d e was p o s s i b l e t h r o u g h t h e use o f t h e C . P . W . mode ( 9 ) . T h e second f l i g h t t o o k place at t h e CNES l a u n c h i n g base a t A i r e s u r I ' A d o u r on 18 S e p t e m b e r 1980. D u r i n g t h i s f l i g h t a g a i n p o s i t i v e a n d n e g a t i v e ions h a v e been m e a s u r e d in d i f f e r e n t modes. T h e use o f t h e C . P . W . mode f o r t h e n e g a t i v e ions p e r m i t t e d an u n a m b i g u o u s i d e n t i - f i c a t i o n o f t h e n e g a t i v e ions u p t o 200 a m i a t an a l t i t u d e o f 35 k m . F u r t h e r m o r e an ion w i t h mass 391 amu was d e t e c t e d f o r t h e f i r s t t i m e , b y Using t h e t e c h n i q u e o f r i s i n g edge d e t e c t i o n . Mass s p e c t r a o b t a i n e d in t h e d i f f e r e n t modes h a v e been p u b l i s h e d in t h e l i t e r a t u r e ( 9 a n d 1 1 ) . In v i e w of t h e r e s u l t s o b t a i n e d i n f l i g h t , as well as t h e e x t e n s i v e l a b o r a t o r y t e s t s t h e p e r f o r m a n c e o f t h e s y s t e m may be c a l l e d v e r y s a t i s f a c t o r y in e v e r y r e s p e c t .

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ACKNOWLEDGMENTS

T h e authors are indebted to the NFWO (Belgian National Science Foundation) for financing part of this project.

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REFERENCES

1. E . E . FERGUSON, i n P r o c . o f t h e N A T O A d v a n c e d S t u d y I n s t i t u t e on A t m o s p h e r i c O z o n e , A l g a r v e 1979, p p . 517-528.

2 . F. A R N O L D , R. F A B I A N , G. HENSCHEN a n d W. J O O S , P l a n e t . Space S e i . , 2 8 , 681 ( 1 9 8 0 ) .

3 . F. A R N O L D a n d R. F A B I A N , N a t u r e , 283, 55 ( 1 9 8 0 ) .

4 . E. AR U S , J . INGELS a n d D . N E V E J A N S , in T e c h n o l o g i e s des E x p é r i e n c e s S c i e n t i f i q u e s S p a t i a l e s , P a r i s 1975, p p . 559-567.

5 . F. A R N O L D , H . B O H R I N G E R a n d G. H E N S C H E N , G e o p h y s . Res.

L e t t . , 5 , 653 ( 1 9 7 8 ) .

6 . J . R. O L S E N , R . C . AMME, J . N . B R O O K S , D . G . M U R C R A Y , D . A . S T E F F E N , R . E . S T U R M a n d G . E . K E L L E R , R e v . S e i . I n s t r . , 49, 643 ( 1 9 7 8 ) .

7. J . I N G E L S , E. AR U S , D . N E V E J A N S , H . F O R T H a n d G.

S C H A E F E R , R e v . S e i . I n s t r . , 49, 782 ( 1 9 7 8 ) .

8 . E. AR U S a n d D . N E V E J A N S , R e v . Sei. I n s t r . , 46, 1010 ( 1 9 7 5 ) . 9 . E. A R I J S , D . NEVEJANS a n d J . I N G E L S , N a t u r e 288, 684 ( 1 9 8 0 ) . 10. W. P A U L , H . P . R E I N H A R D a n d U . VON Z A H N , Z . P h y s . , 152, 143

( 1 9 5 8 ) .

11. E. A R I J S , D . N E V E J A N S , P. F R E D E R I C K a n d J . I N G E L S , G e o p h y s . Res. L e t t . , 8 , 121 ( 1 9 8 1 ) .

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