Circuit Description; General; Principle Of Operation - Philips PM2517E Service Manual

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C I R C U I T D E S C R I P T I O N
3 . 1 .
G E N E R A L
T h e c i r c u i t o f t h e P M 2 5 1 7 c a n b e s u b d i v i d e c i i n t o t h r e e m a i n s e c t i o n s :
- Analog section
- Analog to digital convertor
- Digital section
Each section is described separately with reference to the overall circuit diagram. Basic circuit diagrams of the
varlous stages are inserted in the text wherever necessary as an aid for better understanding of the overall
c i r c u i t d i a g r a m .
T h e c i r c u i t r y o f t h e P M 2 5 1 7 c o n s i s t s o f s p e c i a l m a d e i n t e g r a t e d c i r c u i t s ( L S l ) , d i s c r e t e c o m p o n e n t s a n d
integrated circuits used for display control.
The discrete components are used:
- T o c o n v e r t t h e i n p u t s i g n a l s s u p p l i e d t o t h e i n p u t t e r m i n a l s i n t o s u i t a b l e s i g n a l s ( a t t e n u a t i o n ) f o r t h e
L S I c i r c u i t s .
- A s s i g n a l c o n d i t i o n i n g b e t w e e n t h e L S I c i r c u i t s .
A s L E D d i s p l a y c o n t r o l l C ' s a r e u s e d :
- H E F 4 5 1 1 , B C D t o 7 s e g m ^ n t l a t c h / d e c o d e r / d r i v e r
- H E F 4 5 5 5 , D u a l 1 o f 4 d e c o d e r d e m u l t i p l e x e r .
The LSI circuits used in the PM 2517 are:
O Q 0 0 5 5 . c h a r a c t e r d e c o d e r d r i v e r f o r L E D o r L C d i s p l a y
b O 0 0 5 9 , a i g i t a l c o n t r o l f o r A D C a n d a u t o r a n g i n g c i r c u i t
OO 0060, switching part for ADC with Delta lvlodulation principle (used in combination with OO 0064)
OO 0061. a.c. to d.c. convertor (calculated Rl\4S)
OO 0063, programmable current source for resistance measurements
OO 0064, voltage to current convertor for ADC with Delta lModulation principle (used in combination
with OO 0060).
From the integrated circuits the data sheets are given at the end of this chapter.
P R I N C I P L E O F O P E R A T I O N ( F i s . 1 0 )
3 . 2 .
3-2.1. General
The Pl\tl 2517 consists of:
Analog section
- I n p u t c i r c u i t s
- Dc attenuator
- Ac attenuator
- Ac/dc convertor (OO 0061)
- S h u n t
- Current source {OO 0063)
- Temperature bridge
3-2.2-
Analog section
Switch ing part {OO 0060)
v - | convertor (oo 0064)
Digital section
- D i s p l a y
- ADC control (OO 0059)
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D i s p l a y d r i v e ( O O 0 0 5 5 )
- D i s p l a y c o n t r o l
ADC
3.2.2. |. Direct voltage measurements
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The unknown d-c. voltage is supplied to the d.c. attenuator. Dependent on the range selected the input L
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voltage is attenuated x10 or x1000, From the attenuator the attenuated voltage is directly supplied to the
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A D C w h i c h h a s a s e n s i t i v i t v o f 0 . 1 V o r 1 V .
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