Fluke 732a - Procedure B: Calibration to Standard Cells

732A
CAUTION
To prevent
damage to the
standard
cells,
the
null
detector
used must
open
circuit
Its
input
leads when
the
ZERO/OPR
Switch
Is
set
to the
ZERO position.
1 .
Perform
the
self-calibration
procedure
on the
Precision
Divider
immediately
prior
to
this
procedure.
2. Measure
the standard
cell
enclosure
temperature
per the
manufacturer’s
instructions
and
compute the
voltage
of up
to
9
standard
cells
connected
in series.
Call this voltage
S.
3. Set
the
Null
Detector
to the
ZERO
position.
4.
Connect
the
equipment
as shown
in
Figure
4-
9A.
5. Adjust
the
ZERO control
on the Null
Detector
for a zero
indication
on the
3
ftV
range.
6. Set
the
RANGE
switch
to
the 300uV
range.
7. Set
the
Precision
Divider
ratio
switches
to
S/IO.
8.
Adjust
the Adjustable
Source for
precisely
lOV
output.
9. Set
the
Null
Detector
to OPR.
If the
Null
Detector
reading
exceeds
±
300
^V,
quickly
return
the
Null
Detector to
the
ZERO
position
and
determine
the reason for
the imbalance.
NOTE
If
a high
degree
of
imbalance
exists, check
the
output
of
the Precision
Divider
at its
output
terminals using
Multimeter
A,
It
should
be
approximately
equal to
the
total voltage
of
the
Standard
Cell
bank, or S.
10. Adjust the
Adjustable
Source
for a
null
indication on
the
Null
Detector.
This
is
a
preliminary null.
11. Set the N ull Detector
to
the ZERO
position
on
the
3
uV
range.
Adjust
the ZERO
control
if
necessary for a zero
indication,
12. Disconnect
the
lead
going from the
positive
terminal of the
Standard
Ceils to the Null
Detector
at the Standard Ceil
end
as
shown
in
Figure
4-9B.
Connect
this lead to the
negative
terminal
of the
Standard
Ceils
at
the standard cell
enclosure
as
shown in Figure
4-9C.
13. Set the Precision Divider ratio
switches
to
0. 000000.
14. Set
the Nul!
Detector
to the OPR
postion and
wait for a stable reading.
Note
any offset
(residual
reading).
This reading
represents
the
extraneous
and thermal voltages
which
should
be less than
0.5
pV.
If
the offset
exceeds this
value,
the
cause
should
be investigated and
corrected
before
proceeding.
Adjust
the
Null
Detector
ZERO
control to
obtain
a
null indication.
15.
Return
the
Null
Detector
to
the
ZERO
position.
Do not
disturb
the setting
of
the
ZERO
control.
1 6.
Set the Precision
Divider
ratio
switches
to
the
previously
calculated
value
of
S/IO.
17.
Reconnect the
positive
lead
of the
Standard
Cells
as shown in
Figure
4-9A.
18. Readjust
the
Adjustable
Source,
if
necessary,
for a null indication
on the
3
p\
range
of
the Null
Detector.
19. Do
not
change
the
setting
on
the
Adjustable
Source or the
leads
to the
Precision
Divider.
20. Connect the
equipment
as
shown
in
Figure
4-
10.
21. Repeat steps
12 through
15
for
the
UUT. In
Step
12,
move
the lead
from the
lOV
HI terminal
to
the
iOV
LO terminal of
the
UUT,
22.
Set
the
Precision
Divider
ratio
switches
to
0.999999X.
23. Set
the Null
Detector
to
the
300
p\
range
and
set the OPR /ZERO
switch
to
the
OPR
position.
24.
Decrease
the
range
setting on
the Null
Detector slowly while
adjusting
the
lOV
calibration
potentiometer, through
the
front
panel
opening
on
the
UUT, for a null
indication
on
the
Null
Detector.
Use the non-conducting
adjustment
tool
supplied
with
the instrument,
25. Adjust
the IOV
calibration
potentiometer
to
obtain
a
null
indication with
the
Null
Detector
on
the
3
mV
range. Let
the
system
stabilize
for
about
1
minute before
adjustment,
26.
Connect the
equipment
as
shown
in
Figure
4-
1 1. Reset
the Null
Detector
to
the
3V
range.
4-11