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3. 2.2. 2. Al
ternat in
g
vol
tage m ea
su rement|
The
unknown input
voltage is
supplied
to the a.c. attenuator.
Dependent on
the range
selected
the Inout
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
The conversion of
the
analog
signal into a digrtal
signal is made according the
Delta
l\/odulation
principle.
The
ADC system is built
into
two
LSI circuits.
The
analog
signal is converted into a
data signal.
The duty
cycle of the data signal is
proportional
to the
height of the änalog input
signal of the
ADC
system.
The
ADC
'
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
The digital section consists
of 2 LSI
circuits
(OO
0055 and OO 0059).2
integrated circuits,
display and
discrete
components
for interconnecting the integrated circuits.
ln
the
LSI circuits the complete
control
logic is built
in
(ADC
control, autoranging
control, data control).
Result
The data signal from the ADC, the duty cycle of
which
equals
the input voltage of the
ADC, is supplied to a
counter in the OO 0059.
The result
of
the counter is supplied to the display
Range switching
Manual:
By
means
of switches
(UP,
DOWN) up or down, commands are
supplied to a
range counter.
The output of the range counter switches the relevant ranges
in the attenuators and the
ADC.
Automatic:
In the autoranging mode the output of
the result counter
determines the down
ranging command
(counter
contents
(
00900) and the up
ranging command
(counter
contents
> 10.000).
Overrange
When the counter
contents
is>
10.000
in
^ase
of manual ranging or in the
highest range during
autoranqing
then overrange
is detected.
Polaritv
Dependent to the
polarity
of the data signal
from
the
ADC
the
polarity
is detected.
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