Simpson 260-8XPI, Инструкция по эксплуатации, Страница: 23 / 28

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3.13 Measuring Resistance
Voltage applied to a resistance range will cause reading errors if low and damage
the Instrument if high. When making in-circuit measurements, make certain that
the circuit is completely de-energized before making connections to it.
When making in-circuit measurements, circuit paths in parallel with the resistance
being measured may cause reading errors. Check circuit diagrams for the pres-
ence of such components before assuming that the reading obtained is correct.
a. Before measuring resistance in a circuit, make sure the power is off to the
circuit being tested and all capacitors are discharged. Disconnect shunting
components from the circuit before measuring its resistance.
b. Set the range switch to one of the resistance range positions as follows:
1. Use R X 1 for resistance readings from 0 to 200 .
2. Use R X 100 for resistance readings from 200 to 20,000 .
3. Use R X 10,000 for resistance readings above 20,000 .
c. Set the function switch at either -DC or +DC position. The results are the
same in either position unless there are semiconductors in the circuit ((see
paragraph 3.14). Adjust ZERO OHMS control for each resistance range.
d. Observe the reading on the OHMS scale at the top of the dial.
NOTE: The OHMS scale reads from right to left for increasing values of resis-
tance.
e. To determine the resistance value, multiply the reading by the factor at the
switch position. (K on the OHMS scale equals one thousand.)
3.14 Resistance Measurement of Semiconductors
Make sure that the OHMS range being used will not damage any of the semicon-
ductors (refer to Table 1-1, item 8, Section I).
If there is a “forward” and “backward” resistance such as in diodes, the resistance
should be relatively low in one direction (for forward polarity) and higher in the
opposite direction.
Rotate the function switch between the two DC positions to reverse polarity. This
will determine if there is a difference between the resistance in the two directions.
To check a semiconductor in or out of a circuit (forward and reverse bias resis-
tance measurements) consider the following before making the measurement:
a. The polarity of the battery voltage will be as marked at the jacks when the
switch is in the +DC position and reversed in the -DC position.
b. Ensure that the range selected will not damage the semiconductor. (Refer to
Table 1-1, item 8 and review the specification limits of the semiconductor
according to the manufacturer’s ratings.)
c. If the semiconductor is a silicon diode or conventional silicon transistor, no