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Model 3529A
15.
MEASUREMENTS
OF ALTERNATING
FIELDS.
16.
Measurements
of alternating
fields
can be per-
formed
only by measuring the output of the front-
panel
OUTPUT
jack
with
an
ac
voltmeter
or
an
oscilloscope since the meter on the instrument reads
only the steady-state
value
of the magnetic field.
The
OUTPUT
jack is a de coupled output that gives
one
volt
for
a full-scale
reading
of the field as
selected by the RANGE switch.
CAUTION
-. The signal resulting from the steady-state
value of the magnetic field plus the peak value
of the ac field must not overdrive the ampli-
fliers in the instrument. To check the steady
field
condition,
observe
the
meter;
if the
needle
is
offscale
the
amplifier
may
be
overdriven.
To
check
the ac pick-up,
con-
nect an oscilloscope to the front panel OUT-
PUT
jack
and
observe
the
waveform
for
clipping.
1f either
condition
is observed,
the amplifier is saturating and the instrument
must be switched to a higher range to give a
true
reading.
Because
of the magnitude of
the earth's field, generally ac measurements
must be made onthe 1 AMP or greater range.
SECTION HI
PRINCIPLES OF OPERATION
17.
DESCRIPTION.
18. The Model 35294A is a flux-gate type magnetometer
which operates
in the same
manner
as the standard
probe used with the Model 428A/B. Refer to Section
HI of the Operating and Service Manual for the Model
428A/B for a discussion of the flux-gate principle.
SECTION IV
MAINTENANCE
19. INTRODUCTION,
20. INSTRUMENT. Maintenance of the Model 428A/B
milliammeter
is the same whether the probe used is
the Current Probe Assembly (428A-21A) orthe Model
3529A
Magnetometer
Probe.
Maintenance
of the
Model
428A/B
is discussed in the Model 428A and
428B Operating and Service Manuais, Where differ-
ences between the Current Probe Assembly and the
Model 3529A make it necessary to modify the trouble-
Shooting techniques given in the manual, such modif-
ication
is discussed
below
under
troubleshooting.
21. PROBE,
The Model 3529A
is a simple device,
consisting
of two
drive coils, wound
around forms
containing
core
material,
and an output coil wound
around
both
drive
coils.
In general,
probably the
only troubleshooting technique that will be required
is the ohmmeter
check
described
in paragraph
27,
01364-2
Page 3
22.
MECHANICAL
ZERO-SET.
23,
When
the meter is properly zero-set the pointer
rests
over
the zero
calibration
mark
on the
meter
Scale
when
the instrument is (1) at normal operating
temperature,
(2) in
its
normal
operating
position,
and
(3) turned
off.
Zero-set
as
follows
to obtain
best accuracy and mechanical stability:
a. Allow
instrument
to operate
for
at least
20
minutes; this allows meter movement to reachnormal
operating temperature.
b. Turn
instrument
OFF
and allow 30 seconds for
all capacitors to discharge.
c, Rotate
mechanical zero-adjustment
screw clock-
wise until meter pointer is to left of zero and moving
upscale toward zero.
d. Continue
to rotate adjustment screw clockwise;
stop when
pointer
is right on zero. If pointer over-
shoots zero, repeat steps c and d.
e. When
pointer
is exactiy on zero, rotate adjust-
ment
screw
approximately 15 degrees counterclock-
wise.
This
is enough
to free adjustment screw from
the
meter
suspension.
If pointer
moves
during the
Step you must repeat steps c through e.
24.
TROUBLESHOOTING.
25, If you have another Model 3529A Magnetometer
Probe or another type of probe such as the 428A-21A
Current
Probe
Assembly
or
the
large
aperature
Model
3529A probe,
isolate the trouble to either the
instrument
proper
or to the probe,
by substitution.
If the trouble is in the instrument follow the trouble-
Shooting
procedure
given
in paragraph
29. If the
trouble
appears
to be
in the
probe
see
the next
paragraph.
26. PROBE.
27. If the trouble appears to be in the probe, discon-
nect the probe from the Model 428A/B, and measure
the resistance
across each of the two windings. Only
a few ohms should be measured across either winding
1-2 or winding 3-4 (terminalnumbers appear adjacent
to the pins,
on the face
of the probe connector).
There
shouid be no conductivity between winding 1-2
and winding 3-4,
a. If an examination of the connector indicates the
connector
is defective, note how the wires are con-
nected,
and
then
replace the connector.
This con-
nector is identical to the one used onthe Model 428A/B.
b. If the wires inside the probe or cable are de-
fective, probably the entire assembiy will have to be
repaced
as
the
inside
of the
probe
is filled with
Silastic compound to protect the leads from mechanical
damage.
28. MILLIAMMETER,
29. In general, instrument troubleshooting and main-
tenance
techniques are the same
whether the probe
used
in the 428A-21A
current probe or the Model
3529A magnetometer probe. However,
wherever
the
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