Measuring Voltage (Ac/Dc); Measuring Current - Fluke 87 TRUE RMS MULTIMETER User Manual

Measuring Voltage (AC/DC)

To measure voltage, connect the meter in parallel with the
load or circuit under test. Each of the five ac/dc voltage
ranges presents an input impedance of approximately 10
M in parallel with less than 100 pF. Ac voltage is ac-
coupled to the 10 M input.
To improve the accuracy of dc voltage measurements
made in the presence of ac voltages, measure the ac
voltage first. Note the ac voltage range and manually
select a dc voltage range that is the same or higher than
the ac voltage range. This method improves the dc
voltage accuracy by ensuring that the input protection
circuits are not being activated. A typical application is
measuring the dc offset voltage of an amplifier in the
presence of an ac signal.
Measurement errors due to circuit loading can result when
making either ac or dc voltage measurements on circuits
with high source impedance. In most cases, the error is
negligible (0.1% or less) if the measurement circuit source
impedance is 10 kilohms or less.

Measuring Current

Do not attempt an in-circuit current
measurement where the potential to earth is
greater than 1000V. You may damage the
meter or be injured if the fuse blows while
current is being measured in a circuit which
exhibits an open circuit voltage greater than
1000V.
To measure current, connect the meter in series with the
load or circuit under test. Press the BLUE button to toggle
between alternating and direct current.
If you do not know approximately what the current is,
connect the circuit to the A input terminal first to see if you
have a safe level for the mA A input terminal. Use the
mA A input terminal for current up to 400 mA.
When measuring current, the meter's internal shunt
resistors develop a voltage across the meter's terminals
called "burden voltage." This voltage drop is very low in
your meter, but it may affect precision circuits or
measurements.
Applications
Warning
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