Basic Dc Lnstrument - Datron 1061 Calibration And Servicing Handbook

52
2
3.
4.3.1
Basic DC lnstrument
Equipment
Requ
irements:
4%
digit
Digital Voltmeter
e.g.
Datron 1041
Variable
5V,
1
amp
DC supply
5mV/division
Oscilloscope
e.g'
Telequipment
D83
1MO5% resistor
in
paiallel
with
10nF capacitor
10MS)5%
resistor
in
parallel
with
10nF capacitor
DC
Voltage Calibrator, e.g. Datron 4000/40004
Autocal
Standard.
Procedure
Power Supplies
Turn
instrument
on
and
allow
5
minutes warm-up
period.
4
Connect
DVM
Hi to
TPB
and Lo
to
TP28
on
the
Digital
assembly.
Adjust R2
on the
Rear
(Power
Supplyl pcb
assembly
to give
+5.100V
+25mV'
Connect
DVM Hi
to
TP1
and Lo
to TP20 on
the
Ana-
log
assembly.
Adjust
R7
on the
Rear (Power
Supply)
pcb
assembly
to
give
+15.000V + 15mV.
Connect DVM Hi
to
TP2
and Lo
to TP20 on
the
Ana')
log
assembly.
Adjust
R12
on the
Rear
(Power Sup-
ply)
pcb
assembly
to
give
-15.000V
+
1smv.
13.
lnsert
calibration key into
keyswitch
on the
back
panel and
turn,
placing the
instrument
into
CAL
mode,
NOTE: The display
CAL
tegend
will
be
lit.
14.
Short together pins 'D'
and
'E' on Digital assembly'
NOTE:
All
the
calibration store correction
factors
are
now
reset
to
zero,
15.
Turn
the calibration key
back
to
RUN mode
Analog Assembly
(DC
lsolator
Section)
16.
Centralize R150 and
R160.
17.
Select
0.1V
range DC
with FILTER out.
Apply
a
10MO resistor between instrument
H¡ and
Lo'
Connect
DVM Hi to
TL8,
Lo
to
TP20.
Adjust
FSV
R152
with
a metal
film
resistor
(5Oppm/oC)
for
a
reading
of
<
10mV,
using R159
f
or
'f
ine'
adjustments.
Do not
solder
in
R152.
18.
Apply a
short
circuit
across
the
input
terminals
and
adjust
R
1
50
for
a
reading
of<
50¡rV at TPI
3.
19.
Connect
DVM
Hi to
TP33
and adjust R160
for
a
reading of
<20¡¡V.
20.
Repeat
steps 17
to
19
until
readings
are within
specified limits.
NOTE: The following step
is only
required
after
the
replacement
of
012 or
any component
associated
with
the
temperature compensation
circuitry.
21
. (il
Re-apply 1OMQ resistor across
the
input
terminals. Note the
reading
on the
front
panel
display
(=A).
(i¡)
Note the ambient temperature (=XoC).
(ii¡)
Place
the
instrument
in a
temperature
con-
trglled
oven
at
approx 50oC
without top
cover
and
with Power'on'.
(iv)
Leave
the
¡nstrument
for at
least
t
hour
then
note the
reading
on the display (=B) and
the
temperature
of
the oven
(=YoC)'
(v)
Compute
(B-A)/(Y-X)
=
Drift/oC'
(vi)
Remove
instrument
from
oven
and allow
to
stabilize,
with
power
'on'
to
ambient
for
one
hour.
(vii) lf
the
drift
was
(10
digits/oC
p-roceed
to (x)'
(viii)
For
drifts in
excess
of
10
digits/oC R151
must
be
adjusted.
lf
the
drift
was positive
turn
R151 clockwise.
if
negative
turn
R151
anti-
clockwise'
(ix)
Repeat
from (i).
(x)
Lock
R151
with
a
clean
soldering
iron'
(xi)
RePeat steps 17
to
20.
22.
Solder
in
R152,
with
instrument turned off
'
5.
þ
Digital
Assembly
Switch the instrument
off
and disconnect the
power
lead.
lsolate
the Digital Board
by
removing
the
connectors
along the centre
Panel
(J1-J5).
Connect
variable
5V supply and DVM Hi's
to
TP8,
Lo's
to
TP2g.
Reduce
supply
to
4'750V +10mV.
Set
R83
fully
clockwise. Connect oscilloscope
Lo to
TP28
and
monitor
M53
pin 40' Turn
R83
anti'clock'
wise until TP30
undergoes
a high
to
low
transition
(or
begins
to
Pulse
low).
Remove varíable supply and reconnect
items discon'
nected in
steps
5 and
6.
Disconnect the
oscilloscope.
Switch on
the ¡nstrument'
10.
Connect
DVM Hi
to
battery'positive terminal,
Low
to fP28.
Check
battery voltage
is
>2.5
volts.
11.
Disconnect
DVM
and connect
oscilloscope
Hi
to
Tp25, Lo
to
TP28.
Adjust
scope trigger unt¡l
the
trace is
triggered
by the
first
pulse of
each
reading
burst. Adjust
R11
so
that
the
pulses
occur every
Sms
.t
0.Sms.
12.
Place instrument
into HOLD.
Connect
oscilloscope
Hi
to
TP7.
Adjust L2
to
give a stable +1.05*.0.03V.
NOTE: This
signal contains about 200mV
peak to
peak high
frequency
noise'
7
8.
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