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section 111
Resistance Range
.
c. Deenergize circuit to be measured.
OpenCircuit Volts
(at 1 on top scale)
d. Connect
412A
into circuit,
using
MA/OHMS
and
COM leads.
e.
Energize circuit,
set
POLARITY
switch for
up-scale indication, and read current.
NOTE
When making current measurements,
make
sure
there
is
no connection between
the circuit common
6)
and power line
ground (&)terminals on rear panel.
3-10.
RESISTANCE MEASUREMENT.
a.
Set FUNCTION switch to
OHMS.
b.
If resistance
to
be
measured is part of a circuit,
make sure power is turned off.
c. Connect 412A across circuit
or
component to be
measured, using MA/OHMS and COM leads.
XI
XI0
XI00
X1
K
XlOK
XlOOK
XIM
XlOM
XlOOM
Model
41 2A
d. Set RANGE switch
s o
that meter indication is as
near center scale as possible, and read resistance on
OHMS
scale.
3-1 1. When measuring the resistance
of non-linear devices
such as transistors and diodes, it is often desirable to know
what voltage and current were present in obtaining the
resistance measurement. Table 3-1 lists the open-circuit
voltage and shortcircuit current available at the
412A
leads
during resistance measurements. Voltage and current are
read on the top scale of the meter for all resistance ranges.
The meter reading is directly proportional to the voltage
across the device being measured, and inversely
proportional
to
the current.
As
an example, assume that
a
device being measured on the XI0 range gives a reading
of
.25
on
the resistance scale. The meter
also
indicates
.2
on
the top
scale. Since full-scale voltage for the XI0 range is
100
mV (Table 34), this indicates a voltage of 20 mV
across the device. To determine the current, subtract the
meter reading of .2 from the full scale reading of 1, and
multiply by the shortcircuit current listed in Table 3-1
.
Since the current shown for the X I 0 range is 10
mA,
this
indicates
a
current
of 8
mA through the device being
measured. The resistance measurement, then, indicates an
equivalent resistance of 2.5 ohms, with an applied voltage
of 20 mV, and a current of 8 mA.
Table
3-1.
Voltage and Current in Resistance Measurements
1
10
mV
100 mV
I V
1
v
1
v
I
V
I V
1 v
1 v
ShortCircuit Current
(at 0 on tot, scale)
10
mA
10 mA
10 mA
1
mA
l 0 0 p A
IO
pA
l P A
0.1
pA
0.01 p A
3-2
00
1
29-5
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