Simpson 270-5, Instruction Manual

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Note: The OHMS scale reads from right to left for increasing values of resistance.
e. To determine the actual resistance value, multiply the reading by the factor at
the switch position. (K on the OHMS scale equals one thousand.)
4.19 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 1).
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 internal ohmmeter battery voltage at the (+) positive jack is
identical to the function switch, polarity setting, and opposite to the (-) com-
mon jack.
Make sure that the OHMS range being used will not damage any of the
semiconductors (refer to Table 1-1, item 8, Section 1).
b. If the semiconductor is a silicon diode or conventional silicon transistor, pre-
cautions are not normally required.
c. If the semiconductor material is germanium, check the ratings of the device
and refer to Table 1-1, item 8.
NOTE: The resistance of diodes will measure differently from one resistance
range to another on the same VOM with the function switch in a given position.
For example, a diode which measures 80 ohms on the R x 1 range may measure
300 ohms on the R x 100 range. The difference in values is a result of the diode
characteristics and is not indicative of any fault in the VOM.