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29
Output
T h e o u t p u t s i g n a l o f t h e A D C ( D A T A ) i s a s q u a r e w a v e w h i c h i s d e t e r m i n e d b y t h e c h a r g i n g / d i s c h a r g i n g
t i m e s
o f t h e c a p a c i t o r . C h a r g i n g t h e c a p a c i t o r w i l l g i v e a l o g i c 1 a n d d i s c h a r g i n g w i l l g i v e a l o g i c 0 o f t h e D A T A
s i g n a l . l n t h i s w a y t h e a n a l o g s i g n a l i s c o n v e r t e d i n t o a b l o c k s i q n a l w h i c h i s d e p e n d e n t t o t h e c h a r g i n g a n d
d i s c h a r g i n g t i m e s o f t h e c a p a c i t o r .
L o g i c
' 1
o f t h e D A T A s i g n a l m e a n s u p a n d l o g i c 0 m e a n s d o w n c o u n t i n g o f c l o c k p u l s e s . A s t h e c h a r g i n g a n d
d i s c h a r g i n g t i m e s d i f f e r , a c o u n t i n g r e s u l t i s l c f t i n t h e c o u n t e r a f t e r o n c y c l e , W i t h i n o n e m e a s u r e m e n t ( t w o
measuring periods) a number of cycles are made. The total result of the counter after one measurement is
proportionai to the unknown input voltage Vx.
Note: For every value of Vx a certain number of charging/discharying cycles of which also the times are
different are made within a measurement.
When measuring the DATA signal due to the varying pattern only can be seen if a data signal is present
and how the counter is counting (up or down).
Example of a data signal
Note: The data signal shown in this diagram is not valid for the PM 2517, it only gives an impression of a
data signal in general.
For better understanding for a measuring period of 407 clockpulses is choosen. A measuring period
in the PM 2517 has 12288 clockDulses.
u p
1 0 1
1 0 1
1 0 1
102
d o w n
1
1
1
I
r e s u l t
1 0 0
9 9
'100
1 0 1
r e s u l t
0
0
' l s t
m e a s u r i n g p e r i o d
2 n d m e a s u r i n g p e r i o d
u p
d o w n
1
l
1 . r " 1
1 0 0
102
1 0 1
1 0 1
9 9
102
1 0 0
1 0 0
R E S U L T 8 O O : 2 =
o
0
R E S U L T
O
-
I n t h e 2 n d m e a s u r i n g p e r i o d i n p u t v o l t a g e V x o f t h e O O 0 0 6 4 i s i n v e r t e d f o r a u t o z e r o ( R e f e r t o 3 . 3 . 3 . 2 .
oo 0064).
-
I n t h e 2 n d m e a s u r i n g p e r i o d t h e u p a n d d o w n p u l s e s a r e i n v e r t e d i n t h e O Q 0 0 5 9 .
* The number of clockpulses is divided by two bV the up/down counter in the OO 0059.
The displayed value can be calculated in the Iollowing way:
V i n
N
I ref - R range
2
V i n
= I n p u t v o l t a g e o f t h e A D C
I ref
= Constant reference current. Two ranges available
R range
= Range resistor
N
= Number of clockpulses of one measurement l2x 12288)
5 T 2 5 3 7
.I
.I
I
1
M E A 5 I J F I N G P E R ] O O
I ' I € A 5 U R I N G P € R O D
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