A MICROPROCESSOR BASED SYSTEM FOR W I N D TUNNEL MEASUREMENTS
C.
Ravikumar, lbl.
B a l a k r i s h n a n and V.S.
Holla
D e p a r t m e n t of Aeroepaco E n g i n e e r i n g
Indian I n s t i t u t e of Science, Bangalare, India.
bbatract :
A 1 6 - b i t micoprocessor based system
has
been d e s i g n e d a n d d e v e l o p e d
for
a u t o m a t i c flow f i e l d p r e s s u r e survey and
f o r c e m e a s u r e m e n t s i n t h e l o w s p e e d wind
t u n n e l a t t h e I n d i a n I s t i t u t e of S c i e n c e .
The i n s t r u m e n t a t i o n s u b s y s t e m s t h a t a r e
r e q u i r e d f o r t h e above m e a s u r e m e n t s u n d e r
the
processor
control,
the
system
processor unit,
interfaces t o standard
p e r i p h e r a l s , f u t u r e expansion p r o v i s i o n s
to
other
and
communication
channel
c o m p u t e r s y s t e m s h a v e a l l been d e v e l o p e d
in- house.
Software h a s been designed t o
provide
a
powerful
friendly
and
reconfigurable
integrated
instrumentation.
The s o f t w a r e a l s o e n s u r e s q e a l
time
data
acquision,
on- line
'preprocestling and s t o r a g e o f t h e d a t a on a
floppy.
S o f t w a r e h a s a l s o been d e v e l o p e d
the
data
on
a n i n e x p e n s i v e PC f o r
presentation
i n color graphics.
The
design,
development and i m p l e m e n t a t i o n
d e t a i l s , o f t h e s y a t e m have been p r e s e n t e d
l a thie p a p e r .
i s a blunted c o n i c a l nose 5 h o l e probe.
Both U- tube manometer banks and r e s e r v o i r
t y p e manometer b a n k s a r e a v a i l a b l e f o r
pressure data collection.
For a c c u r a t e
p r e s s u r e m e a s u r e m e n t s a s e t of p r o j e c t i o n
manometers i n d i g e n e o u s l y d e v e l o p e d a t t h e
These
department a r e also available.
m a n u a l l y r e a d manometers have a r e s o l u t i o n
the
of 0 . 2 ~ ~ . I n a t y p i c a l t u n n e l r u n ,
t e s t model i s mounted on t h e m e c h a n i c a l
b a l a n c e ' s t r u t s and t h e aerodynamic f o r c e s
a n d moments a r e measured m a n u a l l y
by
c o u n t e r b a l a n c i n g t h e unknown l o a d s w i t h
dead
weights.
Flow f i e l d d a t a
is
collected
through the pressure
probe,
f i t t e d t o t h e manually operated t r a v e r s e
meachanism a n d a manometer bank o r t h r o u g h
a s e t o f 6 p r o j e c t i o n manometers.
The
p r e s s u r e s u r v e y f r o m t h e body t a p p i n g s is
made w i t h a manometer bank.
For t h e d a t a
reduction,
t h e gathered data i s f i r s t
punched on c o m p u t e r c a r d s and t h e n f e d t o
t h e main frame c o m p u t e r DEC s y s t e m 1090 a t
t h e c e n t r a l computing f a c i l i t y of t h e
institute
..
System O v e r v i e w
Xntroduction :
The c l o s e d c i r c u i t wind t u n n e l (CCWT)
at
the
department
of
Aerospace
Engineering,
Indian I n s t i t u t e o f Science,
h a s been e s t a b l i s h e d i n 1947. The t e s t
s e c t i o n of t h e t u n n e l has an e l l i p t i c a l
c r o s s - s e c t i o n o f d i m e n s i o n s 7 ' x 5' a n d i s
being
used f o r f l o w
field
surveys,
force/moment
and
pressure
survey
measurements.
Recent i n s t r u m e n t a t i o n s e t u p i n c l u d e d a 3-D t r a v e r s e
mechanism
p o w e r e d by i n d u c t i o n m o t o r s ,
pressure
probes,
manometer
banks t o r e a d t h e
p r e s s u r e s and a mechanical balance f o r
f o r c e measurements.
The p r o b e t r a v e r s i n g
i s done t h r o u g h a s e t o f ON/OFF s w i t c h e s
o o n t r o l l e d m a n u a l l y t o move t h e p r o b e i n
t h e r e q u i r e d d i r e c t i o n over a t e s t sect'ion
o f 96" x 48" x 3 6 " .
A set of mechanical
c o u n t e r s a r e used t o i n d i c a t e t h e t r a v e r s e
position.
This arrangement provided a
r e s o l u t i o n o f 0.0025t1 a n d 0.1l'
overall
positionin
The
accuracy
i n probe
pre8sure p r o b e u s e d f o r f l o w f i b f d s u r v e y
.
I n o r d e r t o meet t h e
increasing
demand f o r t h e t u n n e l a v a i l a b i l i t y , t h e
i n s t r u m e n t a t i o n Rystem i n t h e t u n n e l h a v e
b e e n u p g r a d e d t o a u t o m a t e moat o f t h e
e x p e r i m s n t a l p r o c e d u r e s [ I 1. The i m m i n e n t
a d v a n t a g e s due' t o t h i e a r e f a t i t e r a n d
accurate data acquisition that is free
from human e r r o r s , a n d r e d u c t i o n i n t o t h e
a e r o d y n a m i c q u a n t i t i e s , which make t h e
s y s t e m s e l f c o n t a i n e d a n d improve t h e t u r n
a r o u n d time.
The modern t e c h n o l o g y i n t h e f i e l d s
of
wind
tunnel
instrumentation
and
computer based systems,
o f f e r a wide
c h o i c e o f i n s t r u m e n a t i o n and p r o g r a m m a b l e
c o n t r o l l e r s t o automate a t e s t f a c i l i t y .
On t h e i n s t r u m e n a t a t i o n f r o n t , h o w e v e r ,
f o r most o f t h e small- and medium- range
t e s t f a c i l i t i e s , t h e c h o i c e i s l i m i t e d by
several
factors
like
the
present
c i r c u m s t a n c e s of t h e t u n n e l o p e r a t i o n , , t h e
e x h o r b i t a n t c o s t f a c t o r s involved i n t h e
the
required
inatrumentation
and
1
54-IClASF '87 RECORD
CX2449-7/87/0000-004
1
$1.00 @ 1987 UJB
m o d i f i c a t i o n s t o t h e t u n n e l t o accomodat e
new i n s t r u m e n a t i o n .
Due t o s u c h r e a s o n s ,
t h e i n s t r u m e n t a t i o n i n t h e above t u n n e l
h a s been upgraded t o f a c i l i t a t e automation
i n s t e a d o f a c q u i r i n g modern e q u i p m e n t l i k e
[Z-81.
l a s e r doppler velocimeters, e t c .
T h i s u p g r a d a t i o n work i n c l u d e d t h e d e s i g n
and i n t e r f a c e s t o c o n t r o l t h e mechanical
i n s t r u m e n t s , t h e d e v e l o p m e n t o f a new
p r e s s u r e m e a s u r i n g d e v i c e and tin a n t i l o g
DAS. A
d i g i t a l i n t e r f a c e has
been
d e s i g n e d and d e v e l o p e d t o a u t o m a t e t h e 3 - D
p r o b e t r a v e r s e o p e r a t i o n . A new 6 - c h a n n e l
d i g i t a l manometer h a s b e e n d e s i g n e d a n d
developed t o a c q u i r e t h e p r e s s u r e d a t a
from t h e 5- hole probe and t h e t u n n e l f r e e
stream.
This
sensor
is
based
on
automating
the
prassure
measurement
p r o c e s s o f a c o n v e n t i o n a l U- tube manometer
under t h e c o n t r o l of a microprocessor.
I n s t r u m e n t s l i k e s c a n i v a l v e o r a n ESOP [ 7 1
would a l s o c l a i m a p l a c e i n s u c h a n
a p p l i c a t i o n . However, t h e a b i l i t y t o r e a d
all
the
6
channels
accurately
s i m u l t a n e o u s l y o v e r a wide dynamic r a n g e ,
a n d t h e r e l a t i v e l y low c o s t makes i t a
more
suitable
one f o r t h e
present
8ppliCatiOn.
To f a c i l i t a t e t h e a u t o m a t i c c o n t r o l
t h e model a t t i t u d e ,
a new
model
m o u n t i n g r i g h a s been i n s t a l l e d .
The
model m o u n t i n g r i g d e s i g n e d a n d d e v a l o p e d
by
a n o t h e r group i n
the
departbent
provides
the
model c o n t r o l
in
the
d i r e c t i o n s o f p i t c h a n d yaw.
For accurate
force m e a s u r e m e n t s , a s a n o b v i o u s c h o i c e ,
a 6- component s t r a i n gauge b a l a n c e h a s
been a c q u i r e d .
The p r e s e n t and t h e f u t u r e
e x p e r i m e n t a l n e e d s a t t h e CCWT d i c t a t e
t h a t t h e d a t a from t h e s t r a i n g a u g e b a l a n c e
be a c q u i r e d a t a 1 KHz s a m p l i n g r a t e a n d a
r e s o l u t i o n of a t l e a s t 12-blttl.
In view
of
this
and
the
possible
future
expansions,
a 32-channe1,
12- bit d a t a
acquisition
system
(DAS) h a s i b e e n
included.
of
I n o r d e r t o c a t e r t o t h e needs of
p r e s s u r e p l o t t i n g e x p e r i m e n t s and wake
p r e s s u r e s u r v e y s , a 48 p o r t s c a n i v a l v e
v i t h a n LVDT t y p e p r e s s u r e s e n s o r h a s a l s o
been included i n t h e system.
The LVDT
o u t p u t i a a c q u i r e d by t h e DAS.
The
task
of
automating
the
e x p e r i m e n t a l p r o c e d u r e s c o u l d be e f f e c t e d
by
integrating the
above
individual
subaystems with an a p p r o p r i a t e l y s e l e c t e d
programmable c o n t r o l l e r a n d DAS f r o v t h e
commerbially
s e v e r a l high performance,
a v a i l a b l e , o f f - t h e s h e l f computer based
systems.
For example,
systems
like
MACSYM, m a n u f a c t u r e d by Analog D e v i c e s ,
U.S.A.
o r DATA TRANSLATE ( D a t a T r a n s l a t e
[91 e t c . , o f f e r h i g h
Corporation, U.S.A.)
performance s p e c i f i c a t i o n s and a t t r a c t i v e
capabiliti6s.
However, m o s t o f t h e s e
modules are o f g e n e r a l p u r p o s e n a t u r e .
B e s i d e s , t h e r e q u i r e m e n t s i n a wind t u n n e l
c a l l f o r several specialised acquisition
a n d c o n t r o l f u n c t i o n s t h a t c o u l d n o t be
met e a s i l y by t h e c o m m e r c i a l l y a v a i l a b l e
systems.
F o r example, t h e i n t e r f a c e s t o
t h e 3-D t r a v e r s e mechanism and t h e d i g i t a l
manometer a r e t o o s p e c i f i c t o wind t u n n e l
a p p l i c a t i o n s . Commercial s y s t e m s g e n e r a l l y
do n o t meet t h e s e r e q u i r e m e n t s a n d o f t e n
r e q u i r e e x t e n s i v e t c t i l u r i n g , i f chosen.
I
A l t e r n a t i v e l y , t h e above t a s k can be
i m p l e m e n t e d by d e s i g n i n g a d e d i c a t e d c o s t
effective
system p r o c e s s o r u s i n g
the
e a s i l y a v a i l a b l e advanced microproceusors.
A
1 6 - b i t m i c r o p r o c e s s o r system has been
designed
a n d developed t o meet t h e s e
requirements.
The p r e s e n t c o n f i g u r a t i o n
of t h e system i n c l u d e s a CRT terminal f o r
u s o r i n t e r a c t i o n , an i n t e r f a c e t o s t a n d a r d
p r i n t e r s f o r h a r d copy o u t p u t s , a MULTIBUS
i n t e r f a c e f o r any f u t u r e w p u n s i o n s a n d t\
floppy disc controller f o r data atorage.
The
block
diagram
of
the
system
c o n f i g u r a t i o n i s given i n Figure 1.
P o w e r f u l h a r d w a r e w i l l be o f l i t t l e
use without appropriate software.
I n many
applications
the software
development
bears a d i r e c t relationship with
the
a v a i l a b l e hardware.
T h i s often leads t o a
s i t u a t , i o n wherein an i n t e g r a t e d a p p r o a c h
t h a t caters,
with equal emphasis t o b o t h
h a r d w a r e a n d s o f t w a r e a s p e c t s would be
needed f o r a s u c c e s s f u l design e x e r c i s e .
The s o f t w a r e duvtiloped i n a s s e m b l y
l a n g u a g e i n i t i a l i z e s t h o p e r i p h e r a l I/O
chips
and
the
interfaces
to
the
instruments.
The
software f o r
user
a
friendly
interaction,
provides
e n v i r o n m e n t f o r t h e user.
In t h e s e t - u p
mode, a s e t of prompt and h e l p m e s s a g e s
a l l o w s t h e user t o e a s i l y c o n f i g u r e t h e
i n s t r u m e n t s t o t h e s pe c i f ic e x p e r i m en tal.
needs.
The s o f t w a r e t o c o n t r o l
the
e x p e r i m e n t h a s been d e s i g n e d t s s e q u e n c e
t h e c o n t r o l o p e r a t i o n s through t h e d r i v e r
r o u t i n e s f o r , each of t h e
interfaces,
a c q u i r e t h e dn'ta i n r e a l t i m e and p r o c e a s
i t on- line.
The p r o c e s s e d d a t a i 6 e i t h e r
p r i n t e d o r s t o r e d on a f l o p p y i n t h e IBM
format.
The d a t a on t h e f l o p p y c a n a l s o
b e t r a n s f e r r e d t o t h e mainframe c o m p u t e r
DEC 1090 f o r d e t a i l e d a n a l y s i s , i f n e e d e d .
The data p r e s e n t a t i o n i n a n e a s y t o
i n t e r p r e t form,
i s also a n i m p o r t a n t
a s p e c t o f an i n t e g r a t e d s y s t e m . The c o l o r
coded
g r p h i c s t e c h n i u8 d e v e l o p e d
by
Winkleman e t . a l . I l O C f , i s a v e r y u q e f u l
t o o l f o r f l o w f i e l d v i s u a l i s a t i o n and
as i t
requirss
interpretation,
But
s o p h i s t i c a t e d c o m p u t e r systems a n d image
p r o c e s s i n g s y s t e m s i t becomes u n a f f o r d a b l e
f o r s m a l l s c a l e s y s t e m s . However f o r t h u
p r e s e n t s y a t e n , g r a p h i c 8 s o f t w a r e has b e e s
d e v e l o p e d on a n IBM PC c o m p a t i b l e m a c h i n e ,
t o p r e s e n t t h e p r o c e s s e d d a t a in c o l d r
ICIASF '17 HL;COHL)-SS
g r a p h i c s contour p l o t s and v e l o c i t y v e c t o r
plots.
The
package
exploits
the
c a p a b i l i t i e s of t h e PC a n d s i m p l i f i e s t h e
flow f i e l d a n a l y s i s .
A
detailed
description
of
the
hardware
and
software f o r the
user
i n t e r a c t i o n , o v e r a l l experiment automation
and d a t a p r e s e n t a t i o n i s g i v u n below.
t i m i n g a n d power s u p p l y l i n e s .
Modules
t h a t U Y t~ h e MULTIBUS h a v e a m a s t e r - s l a v e
relationship.
The s y s t e m p r o c e s s o r , w h i c h
i s t h e bus m a s t e r ,
d r i v e s t h e command a n d
a d d r e s s l i n e s and c o n t r o l s t h e b u s .
The
p r c o a n t d e s i g n p r o v i d e s s i x a l o t , a for t h o
slave units,
o u t o f which t h e f i r s t s l o t
h a s been u s e d f o r t h e 32 c h a n n e l a n a l o g
d a t a a c q u i s i t i o n system.
A floppy d i s c
c o n t r o l l e r has buun u u u d i n t h e s u a o n d
slot.
System P r o c e s s o r U n i t :
The b l o c k d i a g r a m o f t h e
system
p r o c e s s o r u n i t h a s been shown i n F i g u r e 2 .
The
h e a r t %f t h i s u n i t i s a 1 6 - b i t
microprocessor and numeric d a t a p r o c e s s o r
8086-8087.
The 8086, a t h i r d
pair,
g e n e r a t i o n m i c r o p r o c e s s o r , is c a p a b l e o f
a d d r e s s i n g u p t o I M b 1113.
I t o p e r a t e s on
and t r a n s f e r s 1 6 b i t d a t a a t a t i m e .
The
i n c l u s i o n of 8087 i n t h e d e s i g n * i m p r o v e s
the
processing
speed
phenomenally.
B e s i d e s , t h e 8087's i n h e r e n t c a p a b i l i t i e s
t o o p e r a t e with 8 0 b i t words, p r o v i d e
higher accuracy.
The u n i t has
been
deeigned
t o accommodtite t h e n e c e s s a r y
memory a n d o t h e r programmable p e r i p h e r a l
chips
to
interface
the
subsystems.
N o t a b l e amongest them a r e a
0
0
Programmable p o r i p h o r a l t i m o r s ( I n t e l
825.3)
t o lt,.t.mv utuinp' ~ t i c i I t o q u i k i J d
d a t a titid t o g e n e r a t e t l n i r i r I n t e r r u p t s
f o r t h e data sampling p u r p a s a s ,
-
Programmable
interrupt
controller
( I n t e l 8259)
to
rocess multiple
i n t e r r u p t 6 ( u p t o 8 7 from t h e s u b syiit'Fm niodulev a n d t i n i e r i n t . e r r u p t 3
a n d draw t o t h e a t t e n t i o n o f t h e
p r o c e s s o r when r e q u i r e d (121.
-
Universal
synchron ous
and
a 3y n c h r on o u s
t r a n s m i t t e r / re c e iv e r Y
(Intel
8251)
t o support a CRT
t e r m i n a l f o r u s e r i n t e r f a c e , and t o
p r o v i d e a programmable a u x i l i a r y RS232C c o m m u n i c a t i o n c h a n n e l [I31 f o r
l i n k i n g t h e system t o o t h e r computers
( a PC h a s b e e n c o n n e c t e d t o t h i s
channel).
-
MULTIBUS i n t e r f a c e - t o f a c i l i t a t e
any f u t u r e e x p a n s i o n s ( u p t o 6 ) .
3- D T r a v e r s e A u t o m a t i o n :
T r a v e r s e m e c h a n i s m s may employ e i t h e r
stepper m o t o r s o r i n d u c t i o u n i o t a r s .
One
of t h e i m p o r t a n t f a c t o r s t h a t i n f l u e n c e
t h e c h o i c e o f motors i s t h e c a r r i a g e l o a d .
Stepper motors a r e s u i t a b l e f o r d r i v i n g
light carriages.
But uost often the
c a r r i a g e w e i g h t e n c o u n t e r e d i n ti t y p i c a l
medium and l a r g e s i z e wind t u n n e l s e t u p i s
c o n s i d e r a b l y more.
I n such s i t u a t i o n s
i n d u c t i o n motors a r e p r e f e r r e d t o s t e p p e r
motors.
Several i n t e r e s t i n g p o s s i b i l i t i e s
d o e x i s t for a u t o m a t i n g t h e p r o b e t r a v e r s e
mechanism e m p l o y i n g i n d u c t i o n m o t o r s .
The
technique
employed t o i n t e r f a c e
the
t r a v e r s e mechanism t o t h o 1 6 - b i t p r o c e s s o r
makes i t s i m p l e r t o p o s i t i o n t h e p r o b e
precisely.
'1'11e t 3 ~ ~ ~ v ~ ? tmechanism
rstj
dtnployrtd i n
C C l i T h a s t h r e e n o t o r s t o move
the
p r o b e 9ott a l o n g t h e f l o w d i r e c t i o n (Xdirection),
48"
along
the
lateral
direction
(Y- direction)
and
12"
in
tha
vertical direction
(2- direction).
In
order
t o k e e p t h e t r a v e r s e mechanism
upstream
effects to a
minimum,
the
movement
of t h e c a r r i a g e i n t h e
Zd i r e c t i o n i s l i m i t e d t o 1 ' . To c o v e r t h e
complete 2 - d i r e c t i o n t h e probe h o l d e r r o d
can
be c h a n g e d t o e x t e n d t h e
probe
movement downwards.
Automating
the
above
traverse
mechanism
usipg
the
microprocessor
involves :
(i)
A
F u t u r e expansion p r o v i s i o n s have been
by
designing
a
MULTIBUS
simplified
interface t o t h e p r e s e n t system [14,151.
The
bus s t r u c t u r e p r o v i d e s a
common
e l e m e n t f o r communication between a wide
v a r i e t y o f s y s t e m m o d u l e s which i n c l u d e
memory, d i g i t a l and a n a l o g I/O e x p a n s i o n
It
b o a r d s and p e r i p h e r a l c o n t r o l l e r s .
c o m p r i s e s o f 20 d a t a l i n e s ( e q u i v a l e n t t o
a n a d d r e s s s p a c e o f 1 Mb,),
16 b i directional data lines,
8
multilevel
i n t e r r u p t l i n e s and s e v e r a l bus c o n t r o l ,
a
Probe d i s p l a c e m e n t s e n s i n g o v e r
maximum d i s t a n c e o f 96 i n c h e s .
( i i ) C o n t r o l l i n g t h e t h r e e m o t o r s t o move
the
probe t o t h e r e q u i r e d
position
In a l l t h e t h r e e d i r e c t i o n s
( i i i )C a r r i a g e l i m i t s e n s i n g a t
ends
of
each
of
the
d i r e c t i o n s , and
(iv)
either
three
S o f t w a r e f a r e a s y programming o f t h e
module
One o f t h e w e l l known and a c c u r a t e
methods f o r p o s i t i o n s e n s i n g i s by u s i n g
t h e Gray c o d e s c a l e .
But c o n s i d e r i n g t h e
. . I
+ %
I
56-ICIASF '87 RECORD
span of t h e p r e s e n t system,
a 0.01"
r e s o l u t i o n w i l l n e e d a 1 4 - b i t Grey c o d e
scale.
Due t o t h e o b v i o u s d i f f i c u l t i e s
i n v o l v e d i n f a b r i c a t i n g a 1 4 - b i t Gray code
scale
with
O.O1ll
lines,
often
a
p o t e n t i o m e t r i c method i s u s e d f o r p o s i t i o n
However, i n t h e p r e s e n t
sensing [16].
system,
in
order t o adhere t o
the
simplistic design goal,
an
alternate
method
h a s been d e v e l o p e d .
In this
m e t h o d , p r o v i s i o n s h a v e b e e n made t o counL
t h e number o f r e v o l u t i o n s o f t h e l e a d s c r e w
of
each
motor
with
the
required
r e s o l u t i o n , u s i n g I R o p t i c a l s e n s o r s , MCT8 [17].
The number o f r e v o l u t i o n s a r e
counted
u s i n g a s o f t w a r e programmable
i n t e r v a l t i m e r (8253) i n t e r f a c e d t o t h e
This
avoids t h e problems
processor.
a s s o c l a t t r d w i t h t h o t i n u l o g t o o h n i q u a s . To
c o n t r o l t h e 3 motors, a b i d i r e c t i o n a l
motor c o n t r o l c i r c u i t r y i s d e s i g n e d u s i n g
a simple l o g i c c i r c u i t and r e l a y s . In
order t o safeguard t h e motors a g a i n s t t h e
p r o g r a m a n d human q r r o r s , f e a t u r e s l i k e ,
c a r r i a g e l i m i t s e n s i n g , a u t o - m o t o r OFF a n d
interrupt
to
the
processor
are
incorporated
in
the
design.
The
e l e c t r o n i c i n t e r f a c e i s shown i n
the
Figure 3 .
The
software f o r t h i s
interface
f a c i l i t a t e s c a l i b r a r t i o n of the traverse
and
forms a look- up t a b l e
for4 the
calibration constants.
This calibrbtion
compensates f o r t h e e r r o r s duo t o t h e
inertia
of
the
inducLion
motors,
mechanical g e a r s and a l s o t h e misalignment
e r r o r s i n each a x i s .
For
probe
position control
the
software allows the user t o define the
s c a n volume i n t h e t e s t s e c t i o n a n d o t h e r
parameters.
The f e a t u r e s o f f e r e d by t h i s
aoftwgre include
-
P r o b e movement
selections.
e
I,
S c a n limits
directions.
MANUAL
on
each o f
/
AUTOMATIC
the
Number o f s e g m e n t s w i t h i n t h e
three
limits
i n each d i r e c t i o n .
Different grid sizes f o r different
segments w i t h i n t h e s c a n limits.
Other options i n c l u d e
I,
Default grid s e l e c t i o n .
Grid
size
dynamically
altekable
without discontinuing t h e experiment.
a
C a l i b r a t i o n a n d f o r m i n g a new l o o k - u p
t a b l e f o r t h e correction terms t o
6 - C h a n n e l D i g i t a l Manometer :
The i n s t r u m e n t is b a s e d o n d i g i t a l
r e n d i n g o f t h e d i s t a n c e between t h e l i q u i d
levels
in
a
U- tube
manometer
by
mechanically traversing a c a r r i a g e
to
which a r e f i x e d a p a i r of l i q u i d l e v e l
sensors.
The c a r r i a g e t r a v e r s e i s s e n s e d
b y a d i s t a n c e s e n s o r which p r o d u c e s a
p u l s e p e r O . l m m movement o f t h e c a r r i a g e .
T h e s e p u l s e s a r e c o u n t e d by a f r e e r u n n i n g
counter.
The m i c r o p r o c e s s o r r e a d s t h e
l e v e l s e n s o r s ' s t a t u s and a t t h e i n s t a n t s
of the carriage crossing the liquid level
meniscus,
samples
the
free
running
counter.
The r e a d i n g s a r e s t o r e d i n t h e
s y s t e m memory.
Once t h e s e r e a d i n g s a r e
taken f o r a l l t h e channels, t h e d i f f e r e n c e
in r u a d i n g u fLJr each o f t h u nilrnornetora i e
c o m p u t e d by t h e m i c r o p r o c e s s o r a n d t h e
d a t a i s a v a i l a b l e f o r p r i n t i n g o r any
further processing.
A semi autoniatic version o f t h i s
i n s t r u m e n t , i n which TTL hardware h a s been
u s e d t o r e a d t h e l i q u i d column h e i g h t in a
U- tube
has
been
developed
in
the
d e p a r t m e n t of Aerospace Engineering,
IISc
[ I 81.
However,
in
this
prototype
i n s t r u m e n t , t h e motor c o n t o l i s manual and
a cam m e c h a n i s m i s u s e d f o r t h e c a r r i a g e
movement.
I n view o f t h e r e l a t i v e l y l a r g e
r a n g e o f movement r e q u i r e d f o r t h e p r e s e n t
instrument,
t h e mechanical d e s i g n o f t h i s
p r o t o t y p e h a s been changed c o n s i d e r a b l y i n
t h e new I n s t r u m e n t t o f a c i l i t a t e r e l i a b l e
operation
under the control
of
the
micrprocessor.
The machanical construction and t h e
electronics interface t o the processor
h a v e b e e n shown i n t h e F i g u r e s 4
1791.
The l e n s e e f f e c t of a glasii t u b e f i l l e d
w i t h a l c o h o l i s c o n v e n i e n t l y made u s e o f ,
t o sense t h e l i q u i d l e v e l using I R o p t i c a l
s e n s o r s (MCT-8). The d i s t a n c e t r a v e r s e by
t h e c a r r i a g e i s sensed as a f u n c t i o n o f
the
motor d r i v e s o t h e r e a d i n g s a r e
i n d e p e n d e n t 04 t h e m o t o r s p e e d v a r i a t i o n s .
Although t h e p r e s e n t d e s i g n i n c l u d e s o n l y
6-channels,
w i t h minor e x t e n s i o n s ,
the
i n t e r f a c e c a n be i m p l e m e n t e d f o r a s many
channels
as required with a s u i t a b l e
mechanical set- up.
The r e s o l u t i o n o f t h e s y s t e m i s O . l m m
of
l i q u i d column.
With t h e p r e s e n t
mechanism,
i t may b e n o t e d t h a t t h e
accuracy of t h e readings i s independent
of
t h e speed v a r i a t i o n s of t h e motor.
T h i s e l i m i n a t e s t h a need f o r a p r e c i s i o n
motor and speed c o n t r o l c i r c u i t r y .
The
a c c u r a c y o f t h e u n i t i s f o u n d t o be b e t t e r
The r a n g e o f t h e i n s t r u m e n t
t h a n 0.2mm.
i s +1000mm.
T h e p r e s e n t d e s i ne r e q u i r e s
2 . 5 s e c t o a c q u i r e one s e t o f
samples.
.. ..
.,.?
ICLASF '87 HECOKD-57
thut
I n e t r u m u n t a t i o n f o r Force Moasurumente a n d
Preasure 3urvey0
F o r c e meaaurement i n s t r u m e n t a t i o n
ut
acquisition
has
implemuntud t h r o u g h CI u t r i i i ng:’*ugu
A
b a l a n c e and a 32-channel a n a l o g UAS.
p o s i t i o n e n c o d e r and a m o t o r
control
i n t e r f a c e h a s been d e s i g n e d t o c o n t r o l t h e
m o d e l on t h e new m o u n t i n g r i g d e s i g n e d by
a s e p a r a t e group [ r C O l .
provides
an
overall
t h e system.
The
analog data acquisition
software
r r l l a w 3 tdhu iIBoc t o o o n f i p u r o t h e module t o
the
specific
requiremarit
of
the
experiment.
The c h a n n e l numbers t o be
s a m p l e d , b o u n d s on i n p u t l e v e l s , s c a n r a t e
a n d number o f s a m p l e s f o r a v e r a g i n g a r e
programmable. The a c c u r a c y o f t h e a c q u i r e d
d a t a i s f u r t h e r improved by a u t o m a t i c
d r i f t and g a i n e r r o r c a n c e l l a t i o n s .
Once
t h e module i s d e f i n e d f o r a n e x p e r i m e n t ,
i n o r d e r t o a c q u i r e t h e d a t a , the system
processor
i s s u e s a command t o i n i t i a t e
the
d a t a conversion.
Once t h e d a t a
conversion
is
complete,
the
data
System w i l l i n t e r r u p t t h e
acquisition
p r o c e s s o r s o t h a t t h e p r o c e s s o r may r e a d
the converted data. During the conversion
time,
t h e p r o c e s s o r can e i t h e r proceed
w i t h o t h e r t u s k s a s s i g n e d , o r wait f o r t h e
c o n v e r s i o n t o cornplete.
Thia feature
contributes
t o f u r t h e r processor t i m e
s a v i n g s when t h e module i s used i n t h e
t i m e r i n t e r r u p t mode.
When t h e d a t a
a c q u i s i t i o n i s completct, t h e i n p u t l e v e l s
on t h e s e l e c t e d c h a n n e l s a r e compared
against the set limits.
A
48- port
scanivalve
has
been
i n t e r f a c e d t o t h e system processor a s a
part
of
the
pressure
survey
instrumentation.
6-Component S t r a i n Gauge B a l a n c e :
For a c c u r a t e f o r c e m e a s u r e m e n t s , 6
component s t r a i n g a u g e b a l a n c e h a s b e e n
acquired.
I t h a s e i g h t s t r a i n gauge
b r i d g e s t o i n d i c a t e a l l t h e s i x components
of f o r c e / m o m e n t s .
These e i g h t s t r a i n
gauges provide e l e c t r i c a l s i g n a l s i n t h e
r a n g e o f 22 rnv f u l l s c a l e w i t h e x c i t r r t i o n
voltage of 4 V dc.
The straingauge
b a l a n c e h a s been c a l i b r a t e d f o r u s e i n t h e
p r e s e n t s y s t e m [213.
32- Channel Data A c q u i s i t i o n System :
ri
The
32- channel
data
ncquisitfon
s y s tern ( e x p a n d a b l e t o 256 c h a n n e l s )
has
It c o n s i s t s o f 8
been shown i n F i g . .
c h a n n e l p r e a m p l i f i e r s which a r e t a i l o r e d
t o r e a d t h e s i g n a l s from t h e s t r a i n g a u g e
b a l a n c e , a 32 c h a n n e l m u l t i p l e x e r , a g a i n
selectable instrumentation amplifier, a
s a m p l e and h o l d c i r c u i t and a b u f f e r e d 12b i t succesvive approximation analog t o
d i g i t a l “converter.
The t i m i n g s i g n a l s t o
sequence t h e o p e r a t i o n o f t h e s e blocks
controller
have
been
p r o v i d e d by a
circuitry.
T h i s module i s c o n f i g u r e d f o r
memory mapped I / O a n d t h e a d d r e s s i s
jumper s e l e c t a b l e .
The module h a s b e a n
i n t e r f a c e d t o t h e system processor through
i t s MULTIBUS.
The b l o c k d i a g r a m o f t h e
DAS i s g i v e n i n F i g u r e 5.
..
Expansiori u p t o 2 5 6 c h a n n e l s may be
effected
by u t i l i z i n g
the
expander
c i r c u i t r y w i t h minimum a d d i t i o n a l h a r d w a r e
Other
of p r e a m p l i f i e r s and m u l t i p l e x e r s .
harduare
features
include
signal
c o n d i t i o n i n g a t t h e i n p u t end i n t h e s h a p e
o f h a r d w a r e l o w p a s s f i l t t i r s , nnd i n p u t
over
voltage
protection.
In
its
cpnfiguration, the 8 l o w input chaneels
a c c e p t i n p u t s i n t h e r a n g e o f 2 2mv w h i l e
t h e h i g h l e v e l i n p u t s ~ ~ l l oi nw p u t s o f + 5 v
f u l l scale.
The s e t t l i n g t i m e s o f e z c h
component p u t t o g e t h e r w i l l amount t o 38 u
a e c when t h e o v e r a l l a m p l i f i e r g a i n i s 1 ,
b u t w i l l i n c r e a s e u p t o 100 u D ~ J C f o r a
maximum gtiin o f 1000. These f i g u r e s i m p l y
system
u o c u r t i c y at. 0 . 1 % .
T h i i 3 w o d u l u hus b e o n
wired
f o r i n t a r r u p t modu 01’ o p u r u t l O r i
iir
buan
#--ICIASF ‘117 HECOHD
:;uolpLiirlC:
r*tltuu u p t u
10 K J I Z
Ul‘d
w ti i 1 u o p u i - .1. ~
i r i g th v ti III 1) 1i i’1 u r u
iiiuximiirr guJ.11.
‘The
12 bit dtitu
c ti i e v Z I b 1o
;
S c a n i v a l v s Pressure Measurement System :
’
P r e s s u r e survey expurlments a t t h e
CCWT r e q u i r e m u l t i p l e p r e s s u r e measurement
from a r a k e o f p i t o t t u b e s t r a v e r s e d i n a
v e r t i c a l p l a n e , i n t h e wake o f t h e m o d e l ,
o r from t h e t a p p i n g s drawn from t h e m o d o l
surface.
I n t h e system,
a 48- port
s c a n i v a l v e ( m o d e l 4Sd3) e n a b l e s
these
m e a s u r e m e n t s t o be made u s i n g a s i n g l e
pressure transducer.
F i g u r e 6 shows t h e
b l o c k diagram o f t h e e l e c t r o n i c i n t e r f a c e
t o t h e system processor.
In order t o
o b t a i n t h e p o r t ‘ . n u m b e r s p r e c i s e l y , a 6-bit
o p t i c a l s h a f t p o s i t i o n Gray e n c o d e r h a s
b e e n u s e d on t h e s c a n i v a l v e motor s h a f t .
O p t i c a l Gray e n c o d e r h a s been d e s i g n e d
u s i n g s i x s e t s of I R e m i t t e r a n d s e n s o r
mounted a c r o s s a n o p t i c a l
p a i r s (MCT-8)
c i r c u l a r Gray code d i s c .
The Gray c o d e
p a t t e r n on t h e d i s c w i t h 48 l e v e l s , h a s
b e e n made u s i n g ‘a c o o r d i n a t o - g r a p h t o
A bi- directional
ensure high precision,
m o t o r d r i v e c i r c u i t r y htls been d e s i g n e d
and
developed ( u s i n g t r a n s i s t o r s )
to
c o n t r o l t h e s c a n i v a l v e motor o p e r a t i o n .
Based on t h e d i r e c t i o n arid ON/OFF i n p u c s
t o t h i s block, t h e c i r c u i t d r i v e s the
m o t o r i n t h e u p p r o p r i a t e d i r e c t i o n , and
thus
p r o v i d e s a random a c c e s s o f
8
particular port.
Th B p r i u u in u L I (I 111 u J, L 1 p 1w x IJ J o u L p u L i d
f e d t o a LVDT t y p e p r e s s u r e t r a n s d u c e r
which p r o v i d e s a +5v o u t p u t f u l l s c a l e
w i t h an accuracy o f 0.1% o v e r a range of 0
t o 0.1 p s i .
C h a n n e l 10 o f t h e oarliur
d e s c r i b e d d a t a a c q u i u i t i o n s y Y tem h a s be en
used t o r e a d t h e a n a l o g o u t p u t o f t h i s
transducer.
As a r e s u l t ,
although the
s a m p l i n g r a t e on e a c h c h a n n e l o f t h e d a t a
a c q u i s i t i o n a y s t e m is u p t o 10 KHz, t h e
s a m p l i n g r a t e of t h e p o r t s is l i m i t e d t o
0.4Hz.
T h i s l i m i t a t i o n i s p r i m a r i l y due
to
t h e maxiarum m o t o r s p e e d of
the
e c a n i v a l v e u s e d , which i s 3 rpm.
The s o f t w a r e t o c o n t r o l t h e p r e s s u r e
s u r v e y d a t a a c q u i s i t i o n o f f e r s two modes
of scanivalve operation.
In the f i r s t
mode, s c a n i v a l v e is o p e r a t e d i n s e q u e n t i a l
port selection.
I n t h i s mode t h e p o r t
numbera t o be s a m p l e d a n d t h e s a m p l i n g
r a t e o n e a c h p o r t a r e s e l e c t a b l e by t h e
user b e f o r e s t a r t i n g t h e e x p e r i m e n t . When
t h i s mode o f o p e r a t i o n i s s e l e c t e d , t h e
s y s t e m homes t h e s c a n i v a l v e t o i t s p o r t 0.
Then t h e s c a n i v a l v e motor i s a c t i v a t e 6 f o r
B
c o n t i n u o u s o p e r a t i o n and t h e
port
numbers a r e a o n t i n u o u a l y snmpled.
The
d a t a is a c q u i r e d w i t h i n t h e d w e l l t i m e ,
when t h e p o r t number c o r r e s p o n d s t o t h e
p o r t s t o be s a m p l e d .
The s e c o n d mode
p r o v i d e s a random a c c e s s o f a p a r t i c u l a r
F o r t h i s mode a l s o , s e l e c t c b b l p
port.
p a r a m e t e r s a r e t h e same. However, i n t h i s
mode, t h e s c a n i v a l v e c u r r e n t p o r t number
i s r e a d a n d compared a g a i n s t t h e p o r t t o
be s a m p l e d .
The processor determines t h e
d i r e c t i o n i n which t h e m o t o r h a s t o be
r o t a t e d t o r e a c h t h e n e x t p o r t from which
t h e d a t a h a s t o be r e a d .
Based on t h i s ,
the
proceesor
controls
the
motor
appropriately through t h e i n t e r f a c e .
On
accessing the required port, the data is
a c q u i r e d a8 p e r t h e s e l e c t e d mode.
Lu progr.trei t h 3 riyi t a m f o r h i s
axprimant.
During t h i s e x e r c i s e , t h e software ensures
e r r o r - f r e e parameter s e l e c t i o n through a
s e t o f h e l p m e s s a g e s and s o l f e x p l a n a t o r y
quuriiiu.
Onto l h o tlyutum i u l l ~ e t "f o r t h e
experiment,
the configuration of
the
experiment i s s t o r e d on t h e f l o p p y and t h e
experiment d r i v e r takes- over t h e c o n t r o l
t o initiate
t h o actucil conduct o f t h e
experiment.
T h i s p a r t i n i t i a l i z e s and
c o n f i g u r e s t h e subsystems i n s t r u m e n t a t i o n ,
and performs r e a l - t i m e d a t a a c q u i s i t i o n
and c o n t r o l .
The d a t a i s s t o r e d i n t h e
The s o f t w a r e p r o c e s s e s t h e
floppy disc.
data
on- line
and
also
responds
a p p r o p r i a t e l y t o t h e i n t e r r u p t s from t h e
subsystems instrumentation.
The s o f t w a r e
a l s o c o n t i n u o u s l y u p d a t e s t h o d i s p l a y of
the
status
i n f o r m a t i o n on
the
CRT
terminal.
The u s e r may i n t e r r u p t t h e
process,
through the terminal keyboard,
e i t h e r t o hold/terminate t h e experiment o r
t o modify t h e set- up information.
On
s u c c e s s f u l completion of t h e experiment,
the control i s transfered t o t h s data
presentation eoftware.
The d a t a p r e s e n t a t i o n m e t h o d o l o g i e s
h a v e b e e n f r a m e d b a s e d o n t h e common
e x p e r i m e n t s c o n d u c t e d i n t h e CCWT.
These
into
three
have
been
sub- divided
catogories
i.e.,
flow
field
data
presentation,
f orce/rnoment
data
p r e s e n t a t i o n and p r e s s u r e survey
data
presentation.
The
experiment
driver
s o f t w a r e s t o r e s t h e d a t a on a f l o p p y ,
which c a n be r e a d i l y p r e s e n t e d i n t h e f o r m
of t a b l e s .
The d a t a p r e s e n t a t i o n i n t h e
form o f p l o t s can be obtained e i t h e r
t h r o u g h t h e main- frame computer DEC s y s t e m
1090 o r t h r o u g h an IBM PC c o m p a t i b l e
machine.
The i n t e r a c t i v e n a t u r e o f t h e
p a c k a g e s developed improves t h e u s e r ' s
c o m p r e h e n s i o n o f a l a r g e volume of d a t a by
a choice of c o l o r s / p a t t e r n s ,
Software D e s i g n :
i)
The s o f t w a r e d e s i g n e d f o r o v e r a l l
s y s t e m o p e r a t i o n may be g r o u p e d i n t o t h r e e
p a r t s , i.e.,
( i )systems s o f t w a r e ,
(ii)
user
interaction
software,
(iii)
experiment d r i v e r s o f t w a r e and ( i v ) d a t a
presentation
software.
The s o f t w a r e ,
e x c l u d i n g f o r t h e d a t a p r e s e n t -a t i o n h a s
been d e v e l o p e d i n 8086 a s s e m b l y l a n g a u a g o .
The s o f t w a r e f o r t h e d a t a p r e s e n t a t i o n has
been d e v e l o p e d on a n I B M PC c o m p a t i b l e
machine
so
that the color
graphics
c a p a b i l i t i e s o f t h e PC c o u l d be e x p l o i t e d .
Besides
i t would ease t h e
necessary
modifications t o t h e application software,
which a r e o f t e n r e q u i r e d f r o m time t o
time.
The u s e r i n t e r a c t i o n s o f t w a r e f o r
setting- up t h e experimentation provides a
f r i e n d l y i n t e r f a c e , which e n a b l e s t h e u s e r
S y a t e m s software :
The s y s t e m s o f t w a r e i n i t i a l i z e 8 t h e
p e r i p h e r a l i n t e r f a c e s and submodules f o r
I t also
a p p r o p r i a t e mode o f o p e r a t i o n .
i n i t i a l i z e s the i n t e r r u p t vector t a b l e for
i n t e r r u p t s e r v i c e handler.
The s o f t w a r e
also
ensures
appropriate
proceesor
r e s p o n s e f o r i n t e r f a c e s o f t w a r e and t h e
application software.
i i ) User interaction software :
The h a r d w a r e h a s been d e s i g n e d , as
d e s c r i b e d e a r l i e r , t o c a t e r t o a wide
spectrum of experiments l i k e i ) f l o w f i e l d
s u r v e y , i i ) f o r c e / m o m e n t measurements a n d
iii) p r e s s u r e s u r v e y s ,
w h e r e i n the r a n g e
o f s e v e r a l p a r a m e t e r s , l i k e t h e mode o f
operation
o f t h e sub
modules,
data
'
-
ICliASF '87 HKCOHD 59
ncqui i i t i o n spocificationu utc.,
would
vary.
Hence,
for
any
t;paciFic
e x p e r i m e n t a t i o n n e e d e d by t h e u s e r , t h e r e
i s a need t o r e - c o n f i g u r e , by s o f t w a r e ,
the
individual
sub- systems
and
the
software- generated
time- markers.
The
precise
role
of
the
user- interface
software i s t o acquire t h e set- up data
f r o m t h e u s e r t h r o u g h a s e t o f q u e r i e s and
use
i t t o configure the
sub- systems
accordingly.
The q u e r i e s a r e s e l f - e x p l a n a t o r y and
e a s i l y understandable.
The p e r m i s s i b l e
answers,
parameter
range
etc.
are
d i s p l a y e d along with each query. I n o r d e r
t o ensure e r r o r - f r e e s e t - u p e n t r i e s , t h e
software accepts t h e parameters t h a t a r e
a l l o w a b l e and i n t h e c a s e o f i n c o r r e c t
e n t r i e s , an e r r o r message i s f l a s h e d on
t h e CRT t o warn t h e u s e r a n d r e q u e s t s f o r
a p e r m i s s i b l e answer.
Figures 7 depicts
t h e s e l e c t i o n o f t h e measurement o p t i o n s .
For t h i s s e l e c t i o n , t h e u s e r is a l s o
Once
prompted w i t h t h e expected answers.
t h e r e q u i r e d experiment i s s e l e c t e d , t h e
system
draws t h e u s e r ' s
attention t o
v e r i f y the e n t r i e s (Figure 7 ) .
The u s e r
1s a l l o w e d t o make a n y a l t e r a t i o n s t o h i s
sslaction.
On c o n f i r m i n g t h e o u l u c t i o n ,
d e p e n d i n g on t h e e x p e r l m e n t e s u l a c t u d ,
queries f o r configuring tho individutii
experiments a r e i n i t i a t e d .
F o r example,t o e n t e r the set- up parameters f o r t h e
DAS,
t h e ayst4em d i s p l a y s t h o d t t f a u l t
parameters
required
for
the
data
a c q u i o i t i o n and t h e mode o f r t i w d a t a
output.
F o r t h u c o n v a n i u n c u of' L h u u t l u r ,
t h e c u r s o r , l s p l a c e d a g a i n t i t e a c h of t h o
p a r a m e t e r s 'on t h e s c r e e n , i n t h e o r d e r
shown, a n d waits f o r t h e u s e r r e s p o n s e .
The
eelection
of
the
respective
p a r a m e t e r ' s v a l u e i s f u r t h e r s i m p l i f i e d by
showing t h e a d m i s s i b l e r e s p o n s e / range a t
t h e bottom of t h e s c r e e n .
S i m i l a r p r o c e d u r e h a s been adopted t o
configure
experiments f o r flow
field
survey a n d t h e p r e s s u r e s u r v e y s . F o r f l o w
f i e l d survey, t h e u s e r h a s t o s e l e c t t h e
mode of t h e p r o b e t r a v e r s e c o n t r o l , e i t h e r
T h i s i s f o l l o w e d by
Manual o r A u t o m a t i c .
d e f i n i n g t h e probe t r a v e r s e range a n d t h e
size
i n the three
directions.
grid
Besides, the pressure data acquisition
t h r o u g h t h e 6 - c h a n n e l d i g i t a l manomster
has t o be c o n f i g u r e d .
I n t h e c a s e of t h e
pressure survey experimentation, the u s e r
i s r e q u e s t e d t o s e l e c t t h e p o r t numbers
(of
t h e 48 a v a i l a b l e p o r t s
on
the
s c a n i v a l v e ) t o be s a m p l e d , t h e s a m p l i n g
p e r i o d , a n d t h e number o f s a m p l e s f o r
averaging.
In t h i s f a s h i o n ,
the user
interaction
for
configuring
the
e x p e r l m a n t a hcls b e s n made s e l f - e x p l a n a t o r y
and simple.
The
above u s e r i n t e r a c t i o n
60-ICIASF '87 RECORD
software
f o r . t t r t t y u t - u p has been d e v e l o p e d i n t h e
usuufllI,Ly LUIl~ULLgU 01' ti08L.
I I l > W U V l ~ I . , CiJ I I U W
t h e b a s i c c e n t r a l p r o c e s s o r board and t h e
a s s o c i a t e d h a r d w a r e h a v e been i n t e r f a c e d
t o a n 1BbI PC c o m p c l t i b l c
ii~ichinu,
n
supartltc uzer i n t e r a c t i o n routine which
usus
IBM PC a s a s t a n d - a l o n e
color
t e r m i n a l ha5 a l s o been developed.
The
photograph presented i n Figure 7 i s f r o m
t h e I B M PC t e r m i n a l , which hau an i n i p r o v e d
a p p e a r a n c e a s compared t o t h e b l a c k a n d
w h i t e t e r m i n a l d e v e l o p e d as p a r t o f t h e
systems hardware.
iii) E x p e r i m e n t D r i v e r :
'I'he e x p e r i m e n t d r i v e r p a r t o f t h e
software
c o n f i g u r e s and c o n t r o l s
the
parameter8
subsystems,
based
on t h e
p r o v i d e d by t h e u s e r , a n d a c q u i r e s d a t a i n
r e a l t i m e , The s o f t w a r e a l s o m o n i t o r s t h e
h e a l t h of t h e i n s t r u m e n t s and c o n t i n u o u s l y
u p d a t e s t h e s t a t u s o f t h e e x p e r i m e n t s on
the
CRT s c r e e n .
The u s e r may a l s o
i n t e r r u p t t h e p r o c e s s o r a t any s t a g e o f
t h e experiment, view t h e sot- up p a r a m e t e r s
t h r o u g h s i m p l e commands and a l t e r them f o r
the
rest
of
the
experiment.
The
e x p e r i m e n t d r i v e r s o f t w a r e f o r each o f t h e
a x p e r l m e n t v i s d i s c u s s e d balow.
For f o r c e m e a s u r e m u n t a , d e p e n d i n g o n
t h e user s e t p a r a m e t e r s , t h e i n t h e m a n u a l
mode,
system prompts t h e u s e r t o s e t t h e
model p o s i t i o n i n t h e r e q u i r e d p i t c h a n d
yaw. The u s e r i s t h e n r e q u i r e d t Q s e t t h e
modul
p o s i t i o n a n d p r e s s ' r e t u r n ' on t h e
kuy
b o u r d ( I n t h u u u t , o n i t i L i o m o d u t h u etiiiie
w i l l btt d o n e by t h e tlyutum).
Whuri t h e ktly
i s pressed,
t h e system i n i t i a t e s A / D
c o n v e r s i o n on each of t h e a n a l o g c h a n n e l s
first i n i t i a l i z i n g the timer
for
by
s a m p l i n g p e r i o d a n d t h e n by issuing a
start
c o n v e r s i o n command t o t h e d a t a
a c q u i s i t i o n system.
When t h e a n a l o g t o
d i g i t a l c o n v e r s i o n i s c o m p l e t e , t h e DAS
i n t e r r u p t s t h e processor SO t h a t
the
c o n v e r t e d d a t a i s r e a d by t h e p r o c a s s o r .
The p r o c e s s o r t h a n l o o k s f o r t h e a c q u i r e d
d a t a , and i f t h e d a t a is a v n i l a b l e i n t h e
memory, i t w i l l b e p r o c e s s e d .
A t the
the
i n t e r v a l s o f t h e sampling p e r i o d ,
timer interrupts the processor t o acquire
sampling
the
data
precisely a t the
intervals.
The p r o c e s s o r k e e p s t r a c k o f
t h e number o f s a m p l e s a c q u i r e d a n d when
t h i s number r e a c h e s t h e s a t v a l u e , t h e
timer i n t e r r u p t i s d i s a b l e d and t h e above
process
continues
until
the
data
c o l l e c t i o n a t a l l t h e r e q u i r e d angles i s
complete.
When f l o w f i e l d s u r v e y i s s e l e c t e d ,
t h e d r i v e r software i n i t i a l i z e s t h e 3- D
t r a v e r s e i n t e r f a c e module f o r a u t o m a t i c
probe
positioning.
Thu
probo
i u
positioned
using
the
user
set-up
information a t the t o p l e f t corner of t h e
f i r s t cross- sectional plane i n the test
s e c t i o n . D e p e n d i n g on t h e s t e p s i z e ( g r i d
s i z e ) , i n each of t h e t h r e e directions,
the
probe
i s moved i n t h e
lateral
d i r c e t i o n (Y- direction) i n t h e cross- flow
plane. A t each s t e p , a flow s e t t l i n g time
o f a b o u t 1 second i s a l l o w e d and t h e n t h e
d a t a a c q u i s i t i o n i s e f f e c t e d through the
manometer.
When t h e p r o b e
6- channel
rurraohuu thrr l u r i t gr*Itl pui.rit r i l o n y l,tIiAt,
l i n e , t h e p r o b e i s raoved t o t h e n e x t s t e p
i n t h e v e r t i c a l d i r e c t i o n (downwards) and
the pressure data i s collected.
The
d i r e c t i o n o f t h e p r o b e movement a l o n g t h e
l a t e r a l p l a n e is t h e n r a v u r s u d .
Thi~i
process is continued t o complete
the
After
scanning of each cross- flow plane.
c o l l e c t i n g t h e f l o w f i e l d d a t a from t h e
f i r s t p l a n e , t h e p r o b e t r a v e r s e i s moved
in t h e a x i a l d i r e c t i o n t o p l a c e t h e p r o b e
i n s u c c e s s i v e c r o s s - f l o w p l a n e s and t h e
data
coll.ection
is
completed.
The
pressure
d a t a from t h e 5- hole
probe
throught
t h e manometer s u b s y s t e m i s
a c q u i r e d i n i n t e r r u p t mode.
This approach
makes t h e b e s t u s e o f p r o c e s s o r t i m e a n d
facilitates on- line data reduction while
t h e d a t a i s acquired'.
In
the case of pressure
survey
experiments,
t h e s c a n i v a l v e motor
is
controlled t o access the required ports,
i n s u c c e s s i o n , as p e r user r e q u i r e w n t s .
A t each o f the required
ports,
the
pressure
d a t a f r o m t h e LVDT p r e s s u r e
s e n s o r i s a c q u i r e d t h r o u g h t h e a n a l o g DAS
a a described above.
Once t h o d a t a a c q u i s i t i o n f o r t h e
selectGd experimenta i s completed,
the
d a t a p r o c e s s i n g and p r e s e n t a t i o n s o f t w a r e
receives the control.
T h i s p a r t h a s been
described i n t h e next section.
The a c q u i r e d d a t a , d e p e n d i n g on u s e r
requests,
has
t o be bound
checked,
averaged and norrnalised.
This procesving
i s c a r r i e d o u t by t h e c e n t r a l p r o c e s s o r .
I f t h e d a t a a c q u i s i t i o n r a t e s a r e low, t h e
p r o c e e s o r w o u l d h a v e s u f f i c i e n t time t o
c o m p l e t e this p r o c e s s i n g w h i l e t h e d a t a i s
being acquired.
However, i f t h e i n t e r v a l
b e t w e e n t h e a c q u i r e d d a t a i s small, t h e
p r o c e s s o r would c o n t i n u e t o c o m p l e t e ' t h e
processing a f t e r completion of t h e d a t a
acquisition.
The
acquired
and
the
processed data a r e then written i n t h e
auxillary storage i n a format acceptable
t o IBM PC c o m p a t i b l e m a c h i n e s f o r f u r t h e r
p r o c e s s i n g and p r e s e n t a t i o n .
iv) Data P r e s e n t a t i o n
:
T h i s p a r t of t h e s o f t w a r e t h a t r u n s
o n t h e PC h a s t h e f o l l o w i n g f u n c t i o n s t o
p e r f o r m on t h e a c q u i r e d d a t a .
(i)
Reduction of aerodynamic q u a n t i t i e s
from t h e a c q u i r e d d a t a ,
(ii) Graphical- - Velocity
colour
contour
measured d a t a ,
and
(iii)Force
plots.
and
vector
maps
of
pressure
and
the
distribution
Uuta p r o c e s v i t i g soPtwtlre f o r f o r c e
measurements i n c l u d e s computation o f t h e
aerodynamic c o e f f i c i e n t s .
The l o c a l f l o w
a n g l e a n d t h e v e l o c i t#y m a g n i t u d e h a v e b e e n
o b t a i n e d from t h e Plow f l u l d d a t a , s u n s e d
by t h e f i v e h o l e probe and
t h e probe
From t h i s d a t a
c a l i b r a t i o n d a t a [221.
o t h e r parameters of i n t e r e s t are a l s o
computed.
P r e s s u r e survey d a t a from t h e
m o d e l o r f r o m t h e model wake i s p r o c e s s e d
t o y i e l d t h e load d i s t r i b u t i o n over t h e
b o d y o r t h e p r e s s u r e l o s s i n t h e wake.
T h e s e r e s u l t s a r e used t o c a l c u l a t e t h e
n e c e s s a r y aerodynamic q u a n t i t i e s .
The d a t a p r e s e n t a t i o n s o f t w a r e f o r
the
force
and p r e s s u r e
results
is
i m p l e m e n t e d i n t h e u s u a l manner t h r o u g h
which
multiple c o l o r p l o t 8 of compurable
p a r a m e t e r s c o u l d be o b t a i n e d .
I n t h e cc18e
o f flow f i e l d data presentation,
the
s o f t w a r e developed provides t h e u s e r w i t h
t h e v e l o c i t y v e c t o r p l o t s o n a HP7470
color graphics plotter.
For a quick
v i s u a l i s a t i o n o f t h e flow f i e l d a r o u n d t h e
model,
a
s o f t w a r e package h a s
been
developed t o present t h e velocity d a t a ( o r
l o c a l head l o s s ) i n t h e form of c o l o u r
g r a p h i c c o n t o u r p l o t s on t h e PC.
Uaing
t h i s pcickage~, t h e c o n t o u r s o f s e l e c t i v e
magnitudes
o f t h e f l o w f i e l d may b e
plotted.
Corresponding t o t h e u s e r ' s
choice, t h e software first searches f o r
and s e p a r a t e s o u t t h e iso- magnitude d a t a
from
the velocity
data.
Then
the
equivelocity contours a r e displayed i n
colour graphics.
The r a n g e b e t w e e n t h e
a d j a c e n t c o n t o u r s i s shaded w i t h d i f f e r e n t
colour patteqns.
This provides a q u i c k ,
v i s u a l a p p r e c L a t i o n of t h e f l o w f i e l d
a r o u n d t h e t e s t model i n a n e a s y a n d
if
some
inexpensive
way.
However,
contours are c l o s e l y spaced, depending on
the actual layout of the contours, the
p a t t e r n s u s e d t o s h a d e t h e r e g i o n s may
l e a d t o c o n f u s i o n . T h i s h a s been overcome
by p r o v i d i n g t h e u s e r w i t h an o p t i o n t o
change t h e c o l o u r p a t t e r n s a f t e r examining
t h e c o n t o u r p l o t s p r e s e n t e d on t h e s c r e e n .
T h e a v a i l a b l e c o l o u r p a t t e r n s a r e shown
a d j a c e n t t o t h e p l o t with an i n d i c a t i o n o f
the
d e f a u l t colours a s s i g n e d t o
the
s e l e c t e d magnitude r a n g e s .
Through t h e
k e y b o a r d , t h e u s e r can s e l e c t a p a t t e r n
a n d g i v e a command t o f i l l u p t h e s e l e c t e d
contour
region.
Representative
photographs of t h e c o l o r graphics displays
(CIASF '87 RECORD-41
o f t h e f l o w f i e l d d a t a have b e e n g i v e n i n
The f i n a l formu o f Lha
F i g u r e s 8 and 9.
d i s p l a y s o o u l d a l s o be s a v e d f o r f u L u r e
reference.
[ 8 1 C.F.
[9]
Conclusions :
[lo]
The h a r d w a r e and t h e s o f t w a r e o f t h e
i n t e g r a t e d i n 8 t rumen t a t i o n s y s tem t h a t i s
suitable
t o small s c a l e wind
tunnel
applications
has
been
successfully
d e s i g n e d and r e a l i s e d .
The s y s t e m has
been i n s t a l l e d i n t h e CCWT a t 1 . 1 . S ~ . a n d
tested,
Representative color graphics
p l o t s h a v e been p r e s e n t e d .
Since t h e
i m p o r t a n t f e a t u r e , i n t h e s e p l o t s is t h e
d i f f e r e n t c o l o r s , t h e same may n o t be
e f f e c t i v e l y seen i n t h e f i n a l form of t h e
paper.
However,
we
expect
a
distinguishable gradation i n t h e contour
levels i n t h e f i n a l p i c t u r e s .
[113
[ 121
[131
[14]
Acknowledgements :
[151
The a u t h o r s g r e a t f u l l y acknowledge
t h e A e r o n a u t i c a l R e s e a r c h and Development
Board
f o r f u n d i n g tiis p r o j e c t .
The
authors
wi8h
to
acknowledge
Prof.
Ramssuamy,
Prof.
S.P.
C o v l n d a r a j u arid
Prof, P.R.
Mahapatra f o r t h e i r u s e f u l
suggestions.
The a u t h o r 8 w i s h t o t h a n k
Mi-. B . A . Mtldankumclr f o r h i 8 a c t i v u o u p p o r t
i n t h e p r e p e r a t i o n of t h e manuscript.
4
[I61
[171
[I81
References :
[1 ] C.
[2]
[3]
[4]
[5]
[6]
[7]
Ravikumar, " A M i c r o p r o c e s s o r b a a e d
I n t e g r , a t e d S y s t e m f o r Wind T u n n e l
A p p l i c a t i o n s t ! , M. Sc. (Engg. ) T h e s i s ,
1986.
M. Konig a n d H . J . P f e i f e r , "LDA d a t a
acquisition
systems
with
high
a c c u r a c y and h i g h d a t a r a t e " , ICIASF
'77 R e c o r d , pp. 13- 21, 197'7.
A . B o u t i e r , C. F e r t i n and J . L e f e v r e ,
" L a s e r v e l o c i r n u t e r f o r wind tunnel.
m e a s u r e m e n t s f t , ICAISF ' 7 7 R e c o r d , p p .
1- 12; 1977.
W.J.
Yanta,
"A t h r e e dimensional
l a s e r dopplar velocimeter f o r use i n
wind t u n n e l s b 1 ICIASF ' 7 9 , R e c o r d ,
pp. 294- 301, 1 4 7 9 .
D.W.
Schmidt, " A c c o u s t i c a l methods
f o r f a s t d e t e c t i o n a n d measurement o f
v o r t i c e s i n wind t u n n e l s " , ICIASF ' 7 5
R e c o r d , pp. 216- 228, 1975.
R.H.
E n g l e r , H . H o l s t , D.W. S c h m i d t
a n d R I Wulf, "Measurement o f v o r t i c e s
i n wind t u n n e l e x p e r i m e n t s by U B ~o f
ultrasonic
pulseall,
ICIASF
'79
R e c o r d , pp. 163- 170, 1 9 7 9 .
C.
Meyer, "Wind t u n n e l m e a s u r e m e n t s
with
an
electronically
scanned
m u l t i p o r t p r e s s u r e s e n s o r l l , ICIASFI81
R e c o r d , 1981.
62-ICIASF '87 RECORD
Coe,
P a r r a and R . C .
naw e l u c t r o n i c t i c u n n u r
of
pressure
designed
for
i n s t a l l l a t i o n i n wind t u n n e l modelstl,
ICIASF ' 8 1 R e c o r d , 1981.
IIMACSYM 2 0
Users Manualft, Analog
D e v i c e s , I n c o r p o r a t e d , USA.
A.E.
Winkelmann, and C . P .
TSAO, " A
c o l o r v i d e o d i s p l a y technique f o r
f l o w f i e l d s u r v u y e t f A I A A Journal,
v o l . 2 3 ( 9 ) , p . 1 3 8 1 , September 1 9 8 5 .
t r i A P X 8 6 , 8 8 U s e r ' s Manual", I n t e l
C o r p o r a t i o n , A u g u s t 1981.
Robin
Jigaur,
"Using t h e
8259A
p r o g r am ma b 1e i n t e r r u p t c on t r o 11a r I t ,
Application
Note
AP- 59,
Intel
Corporation, 1979.
"Using
the
8251
Universal
S y n c h r o n o u s / Asynchronous R e c e i v e r /
T r a n s m i 1t e rll
Peripheral
design
handbook,
h t e l Corporation,
pp.
2.241-2.270, August 1981.
David B . G u s t a v s o n ,
tfComputer Buses-A
T u t o r i a l t 1 , I E E E M i c r o , August 1984.
Joe
Barthmaier,
tfXntel multibus
i n t e r f a c i n g f t , A p p l i c a t i o n N o t e , AP
2 8 4 , I n t e l C o r p o r a t i o n , 1979.
Z.M.
Rtimly, E I and W.J.
Ranbird,
ItGomputer controlled system f o r t h e
i n v a u t i g a t i o n of t h e flow
behind
wingsll, J o u r n a l of A i r c r a f t , v o l .
1 4 ( 7 ) , pp. 668-674, J ~ l y . 1 9 7 7 .
llOpto-ulectronics
cornporittnt
Hund
Booktf,
General Instruments,
USA,
1979.
S.P. G o v i n d a r a j u , N. B a l a k r i s h n a n a n d
C.
Ravikumar,
"Development o f a
pressure aensor with d i g i t a l output
b a s e d on a l i q u i d manometer" , P r o c .
o f 1 1 t h N a t i o n a l symposium on f l u i d
m e c h a n i c s a n d f l u i d power, pp. A P l 4 1 9 , December 1 9 8 2 .
C.
Ravikumar a n d N . B a l a k r i s h n a n , " A
low
c o st
m i c r o p r oc e s s o r
based
m u l t i p l e p r e s s u r e m e a s u r i n g system!',
t o a p p e a r i n J o u r n a l of Microcomputer
A p p l i c a t i o n s , Academic P r e s s , v o l .
1 0 , 1987.
S.P.
G o v i n d a r a j u , and V.S.
Iiolla,
" D e s i g n o f k h e p i t c h and t h e yaw
mechanism
for
a
wind
tunnelw',
T e c h n i c a l R e p o r t No; AE-380/A, 1984.
C . R a v i k u m a r , M.A. Ramaswaruy and V.S.
Holla,
"Calibration
of the
six
component s t r a i n g a u g e b a l a n c e for
t h e CCWTII
T e c h n i c a l R e p o r t No .AE397/A, 1 9 8 b .
R . W i c k e n s , P. S o u t h , R.S. Rangi a n d
D . Henshaw, " E x p e r i m e n t a l d e v e l o p m e n t
i n V/STOL wind t u n n e l t e s t i n g a t t h e
national aeronautical establishmenttt,
Canadian
aeronautics
and
space
j o u r n a l , v o l . 1 9 , pp. 145- 154, A p r i l
1973.
Kuuf'firiun,
[19]
/
[20]
L21.1
[22]
C.T.
"A
-
Model c o n t r o l
notors
S h a f t Encoders
.3-D T r a v e r s e
Mechanism
Motors, sensors
ode1 c o n t r o l
-r
r
Interface
for 3- D Probe
Traverse
9
System
.F
P r e s sur e
Tappings
From
-6-channel
Pressure
Ports
@-port
P=ocesa*r
r
Interface f o r
~6-channel
D i g . nanometer
Scanivalve
I
Interface
FIG. 1 .
E
Unit
Computer I
L-----i
CONFIGURATION OF TEE SYSTEM
Merory
(ROM
*
& RAM)
'
/'
Programable
I/O 8255 ( 3 )
Memory
Decoder
I/O
r
BUS
Contr,
I
r
r
CPU
Decoder
Data
Buffer
Addres 8
- 8086
,' L a t c h
I
?
System Proceseor BUS
(Multiplexed)
I
4
MULTIBUS
Interface
Logic
II n t e r r u p t s
V
f
MULTI BUS
FIG. 2.
FIG. 3 .
64-ICIASF '87 RECORD
SYSTEM PROCESSOR U N I T
3-D PROBE POSITION CONTROL INTlEHPAClG
I
I
motor
PUllY
disc vith
holes
optical
s0nsor
Lase U - t u b e s
76
sete)
-\
a).
Motor
Control
I
Circuitry
Optical l i m i t
A
1
Motor ON/OFF
*
I
I
senaore
Lower
Sensor
Circuitry
Upper
\
I
)I n
System
8- bit
latch
+Port
Optical clock
Lower
M e c h a n i c a l Set-up
.
A*
data
P r o ce B sor
b
PPI
8255
Distance
8 Level
Sensor
J
ort
8- bit
latch
I
l
i
I
/
b).
-
ALE
J
E l e c t r o n i c s Interface
FIG. 4.
6
- CHANNEL DIGITAL MANOMETER
ICIASF '87 RECORD -65
Decoder
addrees
FIG. 5 .
32
-
CHANNEL ANALOG DATA ACQUISITIQN SYSTEM
6 bit
a p t i c a l gray
sensor
motor
control
c i r c u i t r y IC
I
ai
24v D C
FIG. 6. SCANIVALVE INTERFACE
66-ICIASF '87 RECORD
Syste.
FIG. 7.
USER INTERFACE
Set-'UP Mode
FIG. 8.
COLOR G R A P H I C S ISOMACNITUDE P L O T S
-a l Equivelocity
Contours at x / d = 2.4
p h a = 18, V i n f = 30 D/S (body :
ogive nose-cylinder body of l/d=10)
Color pattern selection
--
FIG. 9.
COLOR G R A P H I C S P L O T S
- continued
-a f t e r completing t h e color pattern
selection and before saving the picture.
BRIEF BIOGRAPHIES OF AUTHORS
C. Ravikumar graduated in 1979 from Nagarjuna University,
Guntur, India and received M.Sc. degree in engineering physics
and instrumentation in 1981 from Osmania University, Hyderabad,
India.
In 1981 he joined the department of Aerospace
Engineering, Indian Institute of Science, Bangalore, India where
he was employed as a Scientific Assistant.
At the Indian
Institute of Science he had also completed a research oriented
M.Sc.
(Engg) degree.
His
fields of
interest include
microprocessor based instrumentation, microcomputer systems and
computur orig inuering
.
N. Balakrishnan received the BE degree in electronics and
communications from the University of Madras, India in 1972 and
the Ph.D. degree from the department of Aerospace Engineering,
Indian Institute of Science, Bangalore, India in 1979.
In 1973 he joined the Department of Aerospace Engineering
where he is currently employed as Associate Professor.
His
fields of research interest include numerical electromagnetics,
space
craft antennas, computer science and microprocessor
systems. '
Prof. Balakrishnan is a life member of the Instrument
Society of India and is on the editorial board of the Current
Science Journal.
He is the recipient of the UNESCO/ROSTCA award
for outstanding contributions in the area of computers and
informatics for the year 1985. He is the Convener of the Centre
for Microprocessor Applications and also the Centre for Science
He is also a
Information at' the Indian Institute of Science.
consultant to lhading Government and Private industries
..
V.S.
Holla received the B.Sc. (1956) and B.Ed. (1960)
degrees from Mysore University, India, the M.Sc. (Mathematics)
degree from Karnataka University in 1961 and the Ph.D. degree
from Indian Institute of Science, Bangalore, India, in 1969. He
joined the department o f Aerospace Engineering, Indian Institute
of Science in 1965 as a Technical Assistant and is currently an
Associate Professor in Aerodynamics.
His interests are in
Theoretical and Experimental Aerodynamics and has been working in
this area for the last 2 2 years.
Prof. Holla l a a member of the'Aeronautica1 Society of
India.
He is also on the Editorial Boar4 of the Journal of
Aeronautical Society of India, as an Associate Editor since 1980.
68-ICIASF '87 RECORD