section 111 Model 41 2A
.
c. Deenergize circuit to be measured. d. Set RANGE switch so that meter indication is as
near center scale as possible, and read resistance on
d. Connect 412A into circuit, using MA/OHMS and OHMS scale.
COM leads.
3-1 1. When measuring the resistance of non-linear devices
such as transistors and diodes, it is often desirable to know
e. Energize circuit, set POLARITY switch for
up-scale indication, and read current. 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
NOTE
during resistance measurements. Voltage and current are
read on the top scale of the meter for all resistance ranges.
When making current measurements, The meter reading is directly proportional to the voltage
make sure there is no connection between across the device being measured, and inversely
the circuit common 6) and power line proportional to the current. As an example, assume that a
ground (&)terminals on rear panel. device being measured on the XI0 range gives a reading of
.25 on the resistance scale. The meter also indicates .2 on
3-10. RESISTANCE MEASUREMENT. 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
a. Set FUNCTION switch to OHMS.
meter reading of .2 from the full scale reading of 1, and
multiply by the shortcircuit current listed in Table 3-1 .
b. If resistance to be measured is part of a circuit, Since the current shown for the XI0 range is 10 mA, this
make sure power is turned off.
indicates a current of 8 mA through the device being
measured. The resistance measurement, then, indicates an
c. Connect 412A across circuit or component to be equivalent resistance of 2.5 ohms, with an applied voltage
measured, using MA/OHMS and COM leads. of 20 mV, and a current of 8 mA.
Table 3-1. Voltage and Current in Resistance Measurements
1
Resistance Range OpenCircuit Volts ShortCircuit Current
(at 1 on top scale) (at 0 on tot, scale)
XI 10 mV 10 mA
XI0 100 mV 10 mA
XI00 IV 10 mA
X1 K 1v 1 mA
XlOK 1v l00pA
XlOOK IV IO pA
XIM IV
lPA
XlOM 1v 0.1 pA
XlOOM 1v 0.01 pA
3-2 00 1 29-5 |
ACEC
HEWLETT-PACKARD
