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13
Using the Multimeter
Measuring AC Voltage
Riding on a DC Source Bias
To measure AC voltage superim-
posed on a DC voltage source bias
while ignoring the DC voltage, you
must first measure the AC and DC
voltages separately, then compute
the peak voltage using this formula:
Peak voltage = DC voltage + AC volt-
age/0.707
WARNINGS:
• TO AVOID INJURY OR DAM-
AGE TO YOUR MULTIMETER,
NEVER TRY TO MEASURE AN
AC VOLTAGE THAT IS RIDING
ON A DC SOURCE BIAS
WHERE THE PEAK VOLTAGE
EX-CEEDS 100V WITH
RESPECT TO EARTH
GROUND.
• TO AVOID INJURY OR DAM-
AGE TO YOUR MULTIMETER,
NEVER TRY TO MEASURE
ANY VOLTAGE MORE THAN
30V AC ON A DC SOURCE
BIAS.
Follow these steps to measure an AC
voltage superimposed on a DC volt-
age source bias.
1. Set the function selector to one
of the
DCV
positions. Then touch
the test leads to the circuit you
want to test and note the reading
on the upper or lower line of
ACVA/DCVA
on the multimeter.
2. Disconnect the test leads from
the circuit.
3. Remove power from the circuit
under test and discharge all
capacitors.
4. Set the function selector to one
of the
ACV
positions. Then con-
nect a 0.1 microfarad/100V poly-
ester film capacitor in series with
the positive terminal of the volt-
age source and the red test lead.
5. Connect the
–
(common) test
lead to ground and note the read-
ing on the upper or lower line of
ACVA/DCVA
on the multimeter.
The multimeter shows the AC
voltage.
Warning:
To avoid electric
shock, never touch the circuit
and test terminals while testing.
6. When you finish measuring the
AC voltage, disconnect the
power from the circuit under test
then disconnect the capacitor
you connected in Step 4.
MEASURING CURRENT
Measuring DC Current
WARNING:
DO NOT APPLY VOLT-
AGE TO THE TEST LEADS WHILE
THE FUNCTION SELECTOR IS SET
TO
150mA
DC
mA
. THE CONNEC-
TION MUST BE IN SERIES WITH
THE CURRENT.