Measuring Inductances - Philips PM 6302 Instruction Manual

12
2.2.3.
1.
Searching the correct measuring
range in case
of
unknown
capacitance
value
—
Depress push-button
"SEARCH"
—
Switch over the measuring
ranges
—
The
correct
measuring
range
is
found
when
the indicator
points to the "WV"-field
—
Pointer deflection too
small
—*
select
a
lower measuring range
—
Pointer deflection too
large
—
*•
select a higher measuring range.
2.2.
3. 2.
Measuring the capacitance
and
the
loss
factor
D
in case
of
a
known
measuring range
—
With the
vernier adjust the
pointer deflection
to
a
minimum.
—
With potentiometer
"Q/D"
adjust the
loss
factor
D
so that
a
better
minimum
is
obtained
—
Repeat
this
two
adjustments alternately for the lowest
minimum
—
If
no
clear
minimum
can be
reached, depress push-button
"D"
(D
<
1.4;
measuring frequency 100 Hz) and
repeat the
procedure
above.
—
Multiply the
scale reading
by the value selected with the range selector
to obtain the exact capacitance value.
—
To
obtain the
loss
factor
D =
tag 6
read the value adjusted with
potentiometer
"Q/D"
and
multiply
it
by
0.01 or
0.1
depending
on
the position of push-button
"D"
—
When
measuring smaller capacitances substract the
initial
capacitance of
this
instrument
from
the
measured
value.
The
initial
capacitance can
be measured,
when
no sample
is
connected to sockets "l-E".
Note:
If,
when
measuring smaller capacitances,
no
correct
minimum
can be adjusted,
eventually screen
the
sample
for external
mains
stray
fields.
2.23.3.
Measuring
capacitances with
formation
voltage
A
In
order to
form
electrolytic
capacitors
and
in
case
of capacitance
measurements
with
d.c.
bias voltage for
the
sample,
a
mains-independent
battery
can be connected
to
sockets
"DC-BI
AS"
at
the
rear.
The
short-circuit
plug
must then be removed.
Pay
attention for the polarity
of the sample:
"+"
—
*
"I";
"
» "E"
The
a.c.
internal resistance
of the battery
must
be low;
i.e.
under certain circumstances a
capacitor
C p must
be
connected
in parallel
with the
battery;
the value of
C
p
should be higher than
or
equal to the sample capacitance;
but
it
must be
at
least
lOOpF
(see Fig.
5).
In order to protect the
measuring bridge, the
d.c.
current
from the battery must
be
limited
by
a
resistor
Rv.
The
resistance
must be
at least
50
Q
per volt of
the supplied
d.c.
voltage (see Fig.
5).
For measuring the capacitance
and the
loss
factor of the
sample
see 2.2.3.
1.
and
2.2.3.2.
2.2.34. Measuring junction capacitances
In
order to
measure
the junction
capacitance
of a varicap,
proceed
as
follows:
-
Supply an adjustable
d.c.
voltage
from
a
mains-independent galvanic battery
and connect an
external
a.c.
voltage source to
the bridge supply
conform
to figure
6.
—
Connect the
sample with
the
cathode to terminal
I
and
the
anode
to terminal
E.
By stepwise changing
the
d.c.
voltage
and measuring
the
capacitance
of the varicap
in
accordance with
2.2.3.I.
and
2. 2.3.
2.,
the characteristic
of the
sample can be determined.
Note: The
voltage
of
the
external bridge
supply should not be higher than
1
V, in
order
to
avoid
faulty
measurement by
overloading the sample.
2.2.4.
Measuring
inductances
—
Depress push-button
"L"
—
Connect
the
sample
to sockets
"l-E"
2.2.4.
1.
Searching the correct measuring range
in
case of
unknown
inductance value
—
Depress push-button
"SEARCH"
—
Switch over the
measuring ranges
—
The
correct
measuring
range
is
found
when
the indicator points to the
"WV"fie!d.
—
Pointer deflection
too
small
*
select a
lower measuring range
—
Pointer deflection
too
large * select a
higher
measuring range
—
For inductances with
smaller
Q
«
1)
the searching procedure can
indicate
a
range
which
is
one
decade too
low.