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3. 2.2. 2. Al ternat in g vol tage m ea su rement|
T h e u n k n o w n i n p u t v o l t a g e i s s u p p l i e d t o t h e a . c . a t t e n u a t o r . D e p e n d e n t o n t h e r a n g e s e l e c t e d t h e I n o u t
voltage is attenuated x10 or x1000. The attenuated signal is supplied to the RIVIS convertor which has a
sensitivity of 0.1 or 1 dependent to the range selected. The output voltage of the Rl\4S convertor (1 V at
end of range) is supplied to the ADC,
3,2.2.3. Direct and alternating current measurement
The unknown current is supplied to the shunts. Dependent on the range selected (99.00 mA via VO mA
socket or 9.999 A via the '10 A socket) the corresponding shunt is selected. The voltage over the shunt is in
case of A-
measurments supplied directly to the ADC and in case A- measurements first suoplied to the
ac/dc convertor and then to the ADC.
3.2.2.4. R es ista nce m easu rements
At resistance measurements a constant current flows through the unknown resistance which is connected to
the inout terminals of the PM 2511 .fhe constant current is dependent on the range selected.
The voltage over R x is supplied to the ADC via the dc attenuator.
J-2.2,5, I empentufe measurements
At temperature measurements the voltage drop over the resistance thermometer caused by a constant current
is measured. The resistance thermometer is switched in a resistance bridge and is compensated for the resistance
value at 0 oC. The voltage from the bridge is measured by the ADC.
3,2.3,
Analog to digital convedor
T h e c o n v e r s i o n o f t h e a n a l o g s i g n a l i n t o a d i g r t a l s i g n a l i s m a d e a c c o r d i n g t h e D e l t a l \ / o d u l a t i o n p r i n c i p l e .
T h e A D C s y s t e m i s b u i l t i n t o t w o L S I c i r c u i t s . 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 d a t a s i g n a l . T h e d u t y
c y c l e o f t h e d a t a s i g n a l i s p r o p o r t i o n a l t o t h e h e i g h t o f t h e ä n a l o g i n p u t s i g n a l o f t h e A D C s y s t e m . T h e A D C
'
system is also equipped with an automatic zero point correction. The ADC system has an input sensitivity of
0.1 V and 1 V dependent to the range selected.
3.2.4-
Digital section
T h e d i g i t a l s e c t i o n c o n s i s t s o f 2 L S I c i r c u i t s ( O O 0 0 5 5 a n d O O 0 0 5 9 ) . 2 i n t e g r a t e d c i r c u i t s , d i s p l a y a n d d i s c r e t e
c o m p o n e n t s f o r i n t e r c o n n e c t i n g
t h e i n t e g r a t e d c i r c u i t s . l n t h e L S I c i r c u i t s t h e c o m p l e t e c o n t r o l l o g i c i s b u i l t
i n ( A D C c o n t r o l , a u t o r a n g i n g c o n t r o l , d a t a c o n t r o l ) .
Result
T h e d a t a s i g n a l f r o m t h e A D C , t h e d u t y c y c l e o f w h i c h e q u a l s t h e i n p u t v o l t a g e o f t h e A D C , i s s u p p l i e d t o a
c o u n t e r i n t h e O O 0 0 5 9 . T h e r e s u l t o f t h e c o u n t e r i s s u p p l i e d t o t h e d i s p l a y
Range switching
M a n u a l :
B y m e a n s o f s w i t c h e s ( U P , D O W N ) u p o r d o w n , c o m m a n d s a r e s u p p l i e d t o a r a n g e c o u n t e r .
The output of the range counter switches the relevant ranges in the attenuators and the ADC.
A u t o m a t i c : I n t h e a u t o r a n g i n g m o d e t h e o u t p u t o f t h e r e s u l t c o u n t e r d e t e r m i n e s t h e d o w n r a n g i n g c o m m a n d
( c o u n t e r c o n t e n t s ( 0 0 9 0 0 ) a n d t h e u p r a n g i n g c o m m a n d ( c o u n t e r c o n t e n t s > 1 0 . 0 0 0 ) .
Overrange
W h e n t h e c o u n t e r c o n t e n t s i s > 1 0 . 0 0 0 i n ^ a s e o f m a n u a l r a n g i n g o r i n t h e h i g h e s t r a n g e d u r i n g a u t o r a n q i n g
then overrange is detected.
Polaritv
Dependent to the polarity of the data signal from the ADC the polarity is detected.
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