Your meter is designed to apply enough voltage, in the forward biased
direction, to allow current flow. All diodes use up or “drop” a small
amount of the supplied voltage when they are forward biased. When
they are reverse biased they drop nearly all of the supplied voltage. The
voltage drop is normally around 0.4 V for germanium diodes and 0.6 V
for silicon diodes. When the diode is reverse biased, the meter should
indicate the over-range symbol (OFL).
To determine the condition of semiconductor devices:
1. Insert the test leads into the meter (red to the multifunction port
on the right, and black to the common port on the left).
2. Select the diode test function on the rotary function switch.
3. Connect the red test lead to the anode side of the diode, and the
black to the other. There is normally a printed black band around
the anode of a diode.
4. Note the displayed value.
5. Reverse the red and black test leads. Again, note the displayed value.
6. If the digital reading in the first (forward biased) direction
indicates some measurable value, and the reading in the reverse
biased direction shows an over-range (OFL) the diode is good.
7. If the displayed value is low, or all zeros, in both directions, the
diode is probably shorted.
8. If the display indicated an overload (OFL) in both directions, the
diode is probably open. Some diodes, such as those used in
microwave ovens, require a higher biasing voltage than this
meter supplies. UEi has high-power diode test lead adapter sets
accessories available.
Measuring Temperature
Using the K-type thermocouple adapter and the thermocouple, this
meter will display temperatures from 40˚ to 750˚F.
To measure tempera t u r e :
1. Obtain the K-type thermocouple adapter and the thermocouple
from the accessories provided.
NOTE: A wide variety of optional temperature probes are
available from UEi.
2. Insert the adapter into the meter, observing polarity.
3. Insert the temperature probe into the adapter. Again, observe polarity.
4. Place the rotary function switch in the “TEMP” position.
5. Select either the Fahrenheit (˚F) scale or the Centigrade (˚C) scale
using the red “MODE” button.
6. If necessary, prepare a surface to place the hot temperature probe,
once the measurement is made.
7. Using the precautions the task warrants, place your temperature
probe, or thermocouple in position to measure the appropriate
surface, liquid or gas (probes are available for any of these), and
make your measurement.
DL250-MAN P. 6
The voltage or current applied during resistance measurements could
damage some devices. Typically, the voltages applied in the resistance
ranges vary from 3 volts in the lowest range to 0.5 volts in the highest
range. Current will typically vary from 800 µA at the lowest range to 30
µA at the highest range.
To measure resistance:
1. Insert the test leads into the meter, and turn off the power to the
circuit under test. Voltage across the circuit, from any source, will
cause an erroneous reading.
2. Set the rotary switch to the resistance/continuity function. The
meter defaults to the resistance measurement mode.
3. Touch the test probes to the test points and read the display. The
meter beeps as it seeks the correct range to measure the circuits
resistance. Be sure you have good contact between the test leads
and the circuit. Dirt, oil, solder-flux or other foreign matter alters
the reading value.
NOTE: During continuity or resistance measurements, polarity does not
matter. If may be preferable to use the manual range mode to test
some circuits that are susceptible to damage at low voltages/currents.
Measuring Continuity
Use this mode to make quick checks for continuity or electrical circuits,
such as wiring, speaker cables, connections, switches or relays. In the
continuity mode, an audible tone sounds when the value measured is
approximately 50Ω or less.
To test for continuity, follow these steps:
1. Set the rotary switch to the ohms/continuity function.
2. Press the red “MODE” button to bring the symbol up on
the top of the display, indicating that the continuity mode has
been selected. The range is preset to the 400Ω scale and can not
be revised.
3. Place one probe to each side of the circuit to be tested. If
approximately 50Ω or less resistance is in the circuit, the meter
sounds a continuous tone.
Testing Diodes
The diode test function allows you to check diodes, transistors and other
semiconductor devices for opens, shorts and normal operation.
CAUTION!
DO NOT connect the test leads to a source of voltage when the diode
test function is selected.
Diodes, and other P/N junction devices, allow current to flow easily in
one direction and prevent current flow in the other direction. When a
diode is forward biased, it allows current to flow. When it is reverse
biased, it prevents current flow.
