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540B
REF
NAME
REF
FUNCTION
NR.
DESIG
13
SHUNT
J 805
Binding
posts provided
to
accept the Fluke
Model
A40
J 806
Current
Shunts. A
locking screw
for the
larger shunts
is
provided and is
located
on the
rear panel
of
the
Model
A54 plug-in
unit.
Without a Model
A40
plug-in
the
instru-
ment
has a basic current range of 2. 5 to 5 ma.
14
DC INPUT
J
801
Binding posts, with
centers
3/
4 inch apart,
are provided
J
803
for connecting de
voltage
to
the
A54. Connect
the positive
lead to the upper post. The
lower
post
is
chassis
ground.
15
AC INPUT
J
802
A dual purpose AC INPUT connector
arrangement is pro-
J
804
vided
in
the .Model
A54. AC voltages
may
be applied
to
the
unit
through
the UHF type connector or,
since
a
separate
ground post
is
located 3/4 inch from
the UHF
connector's
center,
a standard
dual banana plug.
16
PROTECTION DISABLE
s
803
Disconnects the diode protection circuit in parallel
with the
(Model A54-2 only)
thermocouple, when
depressed.
Depression of
the switch,
while at null
(zero) on the
GALVANOMETER
meter in the
AC TRANSFER
mode, will cause
a deflection.
If
the
de-
flection at each frequency
and on
each range
of interest
is
noted
periodically, the
change
in deflection will
then be an
indication of the long
term stability
performance
of the
transfer
portion of
the unit including the protective
cir-
cuitry.
17
PANEL
BUSHING
NONE
An internally
threaded
bushing used
in
conjunction with
the current
shunt
retaining screw.
Figure
2-2.
FRONT-PANEL CONTROLS, TERMINALS, AND
INDICATORS
(Sheet 2 of 2)
2-5.
Should
lesser
degrees
of
accuracy
suffice
for
any
application, the specifications for
auxiliary
equipment
as
shown
in Figure 2-3
may be
reduced. For
additional
application
information
contact
your Fluke representa-
tive or
the
factory.
2-6
.
METHODS
OF OPERATION
2-7.
There
are many different
methods
of
making
accurate transfer measurements. The methods
outlined
in this
manual
are suggested as being
adequate.
Infor-
mation about transfer measurements, methods, theory,
etc. may be found in
the
following
references:
a.
THERMAL CONVERTERS
AS AC-DC TRANSFER
STANDARDS FOR CURRENT
AND
VOLTAGE
MEAS-
UREMENTS AT AUDIO
FREQUENCIES,
F. L.
Hermach, J. Research
48, 121
(1952}
RP2296.
b.
A
WIDE-RANGE
VOLT-
AMPERE
CONVERTER
FOR CURRENT AND VOLTAGE MEASUREMENTS,
AlEE Transactions, Communications
and
Elec-
tronics, Paper
No.
59-161 (1959}. F. L.
Hermach
and
E.
S. Williams.
c.
CALIBRATION OF VOLT-AMPERE
CONVERTERS,
National Bureau
of Standards
Technical
Note 188,
(1963} E.
S.
Williams.
2-8.
PRELIMINARY OPERATION
2-
9.
PRECAUTIONS
2-10.
High order
accuracy
can
be
obtained
with this
Transfer
Standard only if the
user is
aware
of
certain
limitations
and takes appropriate precautions as
follows
:
a.
Bead
type thermocouples,
like
that
used in the Model
540B, exhibit
a
small exponentially decreasing drift
of emf after a steady heater current
is initially
applied. Allow approximately 10 minutes
for
the
thermocouple element to stabilize. After the
stabi-
lization
time, the drift
should
be less
than
2 small
divisions
per minute
in the HIGH sensitivity
position.
When
changing
to different
levels
of input, after
the
stabilization
period,
a wait
of only a few minutes
is necessary
before
continuing
with
measurements.
Any observed drift should be evaluated
quanti-
tatively.
b.
Connection
errors
should be evaluated
and
mini-
mized
when the Transfer Standard
is
used to
cali-
brate other instruments. These errors can often
be
detected by changing the length and
position
of
the
leads.
Short coaxial
leads should
be used when
possible.
These errors
can be significant
at high
test frequencies.
2-3
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