Table of Contents
Advertisement
The second secondary, through l e a d s 8 , 9 , and 1 0 , i s r e c t i f i e d by
A -15 v o l t s u p p l y i s g e n e r a t e d by C2, C5 and t h e n e g a t i v e 1 5 v o l t
CR1-4.
v o l t a g e r e g u l a t o r U35.
T h i s v o l t a g e i s used p r i m a r i l y by t h e
A/D
c o n v e r t e r .
A +15 v o l t s u p p l y i s g e n e r a t e d by
C 4 and t h e p o s i t i v e 1 5 v o l t v o l t a g e r e g u l a t o r
U 3 3 .
T h i s +15 v o l t s u p p l y i s a l s o used p r i m a r i l y by t h e
A/D
c o n v e r t e r .
A
t h i r d v o l t a g e produced through t h i s primary i s a +12 v o l t s u p p l y g e n e r a t e d
by C 1 , C 3 , and t h e p o s i t i v e 1 2 v o l t v o l t a g e r e g u l a t o r U32.
The +12 v o l t
s u p p l y i s used t o d r i v e t h e m i c r o p r o c e s s o r .
The t h i r d secondary i s o u t p u t e d t h r o u g h l e a d s 1 4 and 1 5 and i s
r e c t i f i e d by CR9-12.
A f l o a t i n g 1 5 v o l t s u p p l y i s g e n e r a t e d by C40 and a
p o s i t i v e 1 5 v o l t v o l t a g e r e g u l a t o r U36.
T h i s f l o a t i n g 1 5 v o l t s u p p l y i s
used t o s u p p l y t h e c o n s t a n t c u r r e n t s o u r c e .
4 . 3 . 2
P r e c i s i o n C u r r e n t Source
The d i o d e c o n s t a n t c u r r e n t s u p p l y i s s u p p l i e d by t h e p r e c i s i o n
c u r r e n t s o u r c e U22.
A r e f e r e n c e v o l t a g e used by t h e c u r r e n t s o u r c e
i s
d e r i v e d from a n i n t e r n a l t e m p e r a t u r e s t a b i l i z e d p r e c i s i o n v o l t a g e r e f e r e n c e
of 6.95 v o l t s between p i n s E and C of U22.
R e s i s t o r s , R12A, R 1 3 , R14 and
t r i m p o t R12 v a r y t h i s v o l t a g e t o match t h e v o l t a g e g e n e r a t e d by feedback
r e s i s t o r R19.
R e s i s t o r R19 h a s been s e l e c t e d t o g e n e r a t e 4.99 V (by t h e
f e e d b a c k c u r r e n t o f 10 microamps).
The trimmer r e s i s t o r R12 a l l o w s f o r an
a d j u s t m e n t of t h e r e f e r e n c e v o l t a g e t o e q u a l t h i s f e e d b a c k v o l t a g e .
The
10 microamp o u t p u t c u r r e n t i s f e d through p i n s G and B of U22 t o t h e s e n s o r
c o n n e c t o r ( s e e F i g u r e 2.1).
4.3.3
A/D C o n v e r t e r
The a n a l o g - t o - d i g i t a l
c o n v e r t e r c o n s i s t s of a p r e c i s i o n 4½ d i g i t
I . C .
p a i r t h a t produces a m u l t i p l e x e d BCD o u t p u t t h a t i s a c c u r a t e t o
±1
count o v e r t h e e n t i r e 40,000 count r a n g e .
The 7 1 3 A r u n s on a 50 K
Hz
c l o c k
g e n e r a t e d by
U1.
T h i s c l o c k frequency a l l o w s f o r one r e a d i n g e v e r y .8
seconds ( s i n c e one c l o c k p u l s e
i s
r e q u i r e d t o make one c o u n t ; 50,000 p u l s e s
p e r second would a l l o w f o r 1 . 2 r e a d i n g s p e r s e c o n d ) .
i s o u t p u t e d i n a b i t - p a r a l l e d ,
b y t e - s e r i a l form.
i s m u l t i p l e x e d by U12 and c o n v e r t e d t o a u s e a b l e f o r m f o r t h e m i c r o p r o c e s s o r .
The d i g i t a l s i g n a l
The A/D c o n v e r t e r o u t p u t
4.3.4
M i c r o p r o c e s s o r Hardware
The microcomputer used i s a n F8 m i c r o p r o c e s s o r i n a 3850/3853
c o n f i g u r a t i o n .
The 3850 i s t h e C e n t r a l P r o c e s s i n g U n i t (CPU) and c o n t r o l s
e x t e r n a l s u p p o r t l o g i c .
f o r d a t a t r a n s f e r between t h e 3850 and l o g i c e x t e r n a l t o t h e m i c r o p r o c e s s o r .
The t e m p e r a t u r e d e t e r m i n a t i o n program and b r e a k p o i n t d a t a ( p l u s c o n t r o l
program) a r e s t o r e d i n 2048-bit b i p o l a r PROMS (256 b y t e s x 8 b i t s p e r b y t e ) .
The CPU r e a d s t h e program through t h e SMI.
The CPU h a s two b i - d i r e c t i o n a l ,
8 b i t
I/O
p o r t s
Advertisement
Table of Contents
