Amprobe LCR55A Inductance-Capacitance-Resistance-Meter - Manual (Page 6)

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Overload Indication
Range overload is indicated by a “OL” in the display with all
other digits blanked. Overload indication is normal in the
OHMS range with open circuit or too high a resistance.
Preparation for Use – Unpacking
Your shipping carton should include the LCR55A, one test lead set (one black,
one red), one pair of alligator clips, one 9V battery (installed), one spare
0.1A/250V fuse (inside the case), one holster, a warranty card and this manual. If
any item is damaged or missing, return to the place of purchase for an exchange.
Measuring Procedures
General Procedures
1. When connecting or disconnecting test leads to/from a circuit, always first
turn off power to device or circuit being tested and discharge all capacitors.
2. If the magnitude of a signal to be measured is not known, set selector switch
to highest range first and reduce until satisfactory reading is obtained.
3. Strictly observe the max input limits.
Resistance Measurement (Fig. -1-)
1. Turn off power to the resistance to be measured and discharge any
capacitors. Any voltage present during a resistance measurement will cause
inaccurate readings.
2. Connect red test lead to +Rx Input and black test lead to -Rx Input.
3. Set Function/Range Switch to the desired Ω position.
4. Connect test leads to resistance or circuit to be measured.
5. Read resistance value on Digital Display. Open circuits will be displayed as an
overload condition.
Note: On the 20Ω range, an adjustment potentiometer (ZERO ADJ.) allows you
to zero out the test lead resistance. Short test leads and adjust the knob until the
display reads zero.
Diode and Transister Test (Fig. -2-)
The diode test measures the voltage drop across the diode junction.
4. Connect the red test lead to the +Rx Input and the black test lead to the –Rx Input.
5. Set the Function/range switch to � or to � M.W. position (to test diodes
found in microwave ovens).
6. Apply probe tip of red lead to the anode and black lead to the cathode
of the diode. The meter’s display indicates the forward voltage drop
(approximately 0.7V for silicon diode or 0.4V for germanium diode). Meter
will display overload condition for an open diode.
7. Reverse test lead connections to the diode to perform a reverse bias test.
Overload indicates a good diode.
Note: Overload condition for both reverse and forward bias tests indicate an
open diode. A low voltage reading for both bias tests indicates a shorted diode.
If the diode is shunted by a resistor of 1000 ohms or less, it must be removed
from the circuit before taking the measurement. Bipolar transistor junctions may