Philips PM2517E Service Manual page 32

Automatic digital multimeter

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3.3.2-3- D.c, current Measurements (Fig. l4)

- T h e i n p u t c i r c u i t f o r d . c . c u r r e n t m e a s u r e m e n t s

i s s h o w n i n f i g u r e 1 4 .

- R a n g e 1 0 0 m A - .

l n t h e f u n c t i o n m A : - : : o n l y 1 0 0 m , A r a n g e i s a v a i l a b l e . T h e 1 0 0 m A r a n g e i s d e t e r m i n e d b y s h u n t s R 6 0 3

and R

'1.

Resistor R 605 is used for adjusting the 100 mA range.

- Protection

T h e

' 1 0 0

m A r a n g e i s p r o t e c t e d b y f u s e F 1 ( 3 ' 1 5 m A q u i c k ) .

W h e n i n c a s e o f m e a s u r i n g i n t h e v o l t a g e f u n c t i o n , i s s w i t c h e d o v e r t o t h e ( m ) A f u n c t i o n w i t h t h e v o l t a q e

s t i l l o n t h e i n p u t t e r m i n a l s , t h e n d u e t o l o w r e s i s t a n c e v a l u e s o f t h e s h u n t s a h i g h c u r r e n t i s s w i t c h e d .

T h e h i g h c u r r e n t c a n d a m a g e t h e f u n c t i o n s w i t c h . T o p r e v e n t t h i s t h e ( m ) A r a n q e i s a l s o p r o t e c t e d b y

m e a n s o f a s w i t c h p o s i t i o n ( m ) A ' - .

w h i c h i s s i t u a t e d b e t w e e n t h e p o s i t i o n s o f t h e i u n c t i o n s o C a n d

( m ) A -

i n t h e f u n c t i o n s w i t c h . I n t h i s c a s e t h e i n p u t i s f i r s t c o n n e c t e d w i t h N T C r e s i s t o r R 6 0 1 .

W h e n t h e i n p u t v o l t a g e a t t h e i n p u t i s t o o h i g h t h e n f u s e F 1 w i l l b l o w .

R a n g e

' 1 0

A -

T h e 1 0 A r a n g e i s d e t e r m i n e d b y s h u n t R 1 ( 1 2 m Q ) . T h e 1 0 A s h u n t i s a d j u s t e d b y r e s i s t o r R 6 0 8 .

- I n t h e d i g i t a l s e c t i o n o f t h e P M 2 5 1 7 s w i t c h i n q f r o m t h e , ] 0 0 m A t o t h e 1 0 A r a n g e i s e f f e c t e d i n t h e

f o l l o w i n g w a y :

W h e n a b a n a n a p l u g i s i n s e r t e d i n t h e 1 0 A s o c k e t t h e d i s p l a v i s s w i t c h e d f r o m 1 0 0 m A t o 1 0 A . T h i s

i s d o n e b y m e a n s o f t h e 1 0 A s w i t c h w h i c h i s b u i i t i n t h e 1 O A s o c k e t .

R a n g e

I n p u t F D

o o 0 0 5 5

1 0 0 m A

. 1 0 A

- G e n e r a l

R e s i s t o r R 6 1 0 i s u s e d t o g e t a n e q u a l l o a d i n t h e l m ) A - a n d ( m ) A -

f u n c t i o n .

T h e A D C h a s a n i n p u t s e n s i t i v i t y o f 0 . 1 V i n c a s e o f d c c u r r e n r m e a s u r e m e n r s .

3.3.2.4. A.c. current measuremenTs (Fig. l5)

- T h e i n p u t c i r c u i t f o r a . c . c u r r e n t m e a s u r e m e n t s

i s s h o w n i n f j g u r e 1 5 .

- The a.c. input current range 100 mA is shunted and adjusted in the same wav as d.c. currents (refer to

3 . 3 . 2 . 3 . ) . T h e v o l t a g e f r o m t h e s h u n t s ( 0 . 1 V e n d o f r a n g e ) i s s u p p l i e d t o t h e V i n 1 i n p u r o f t h e a . c . / d . c .

c o n v e r t o r 0 O 0 0 6 1 v i a s w i t c h m A - a n d C 6 0 1 . I n p u t V i n 2 o f t h e 0 0 0 0 6 1 i s d i s c o n n e c t e d f r o m t h e

i n p u t c i r c u i t s , b y m e a n s o f c o n n e c t i n g - 8 . 5 V s u p p l y r o t h e g a t e s o f V 3 0 1 a n d V 3 0 2 . S i g n a l R N G B

h a s n o i n f l u e n c e { a l s o r e f e r t o a . c . v o l t a g e m e a s u r e m e n t s

3 . 3 . 2 . 2 . ) .

R A N G E

B N G B

R N G A

I n p u t

AC/DC convertor

l n p u t

A D C

0 . 1 v

T h e A C / D C c o n v e r t o r h a s a n i n p u t s e n s i t i v i t y o f 0 . 1 V i n t h e a . c . c u r r e n t r a n g e s .

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