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13
DESCRIPTION
When
making
a
normal
measurement
(..PO...)
the
microcomputer
sets
all
the
relays
and FET's
which
are
necessary to
make
a
measurement. For
instance: Select
the
Vtt.
function
and
the range
200mV.
The
relays
and FET's which
are
now
set
can be
found
in
the
relay table.
So
ft
is
possible to
determine
if
the
relays are really
set.
When
making
an
AUTOCAL
0,1V
(..PI
...)
the
microcomputer programs
the
OQ
0063
so that
a
current of
100
(jA
flows through
R606, which
causes
a voltage
drop
of
lOOmV
across
it.
With
this test
it is
possible
to
measure
this voltage.
In
the position
AUTOCAL
IV
(..P5...)
the
microcomputer programs
the
OQ
0063
to
give a
current of
1mA
through
R606. The
result
is
IV
across
R606.
With
the
I
ZERO
measurements, normally
the
offset
is
measured
in
the
I—
V
convertor, (current
offset).
In
the
..P3...
and
the
..P7...
tests
these
IZERO
measurements
are
simulated,
(see
relay
table
on
page
52 and
page
53
of the
PM2521
service
manual).
In
all
these
tests
(..PO...
to
..P7...)
the
AZ
status
can be changed. This
means
that the input of the
ADC
can be
selected.
To
do
this
push
the
+/—
button.
Thanks
to
this
it is
possible
to
measure
the input
voltage,
or the voltage across the
R606
resistance,
on
the
input of the
ADC
(pin
5 and
pin
10
of the
OQ
0064)
Example:
When
there
is
no
input
signal,
the voltage
on
pin
5 and
pin
10 of the
ADC
is
0,460V.
(with respect tot the
0
input socket)
Set
200mV
on
the input
terminals.
After attenuation the
voltage
on
point
6
of
A601
is
lOOmV.
This
voltage of
lOOmV
causes
either
a
voltage of
0,360V on
pin
5
of
A602
or
a
voltage
of
0,360V
on
pin
10
of
A602,
depending
on
the
state
of the
AZ
flip-flop.
(0,460V— 0,1V
= 0,360V).
So
the input
voltage
after
attenuation degrees the
voltage
on
pin
5 or
pin
10 corresponding
to the
input
signal.
/
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