Fluke 87 III - Manual (Page 21)

Making Measurements
13
The following are some tips for measuring voltage:
•
When you measure voltage, the meter acts
approximately like a 10 M
Ω
(10,000,000
Ω
)
impedance in parallel with the circuit. This loading
effect can cause measurement errors in high-
impedance circuits. In most cases, the error is
negligible (0.1% or less) if the circuit impedance is
10 k
Ω
(10,000
Ω
) or less.
•
For better accuracy when measuring the dc offset of
an ac voltage, measure the ac voltage first. Note the
ac voltage range, then manually select a dc voltage
range equal to or higher than the ac range. This
procedure improves the accuracy of the dc
measurement by ensuring that the input protection
circuits are not activated.
MIN MAX RANGE HOLD H
Hz REL
mA A
mV
V
V
OFF
!
!
1000V MAX 400mA MAX FUSED 10A MAX FUSED
PEAK MIN MAX
µ A
CAT II
V
87 TRUE RMS MULTIMETER
MIN MAX RANGE HOLD H
Hz REL
mA A
mV
V
V
OFF
!
!
A COM V mA µ A
A COM V mA µ A
1000V MAX
400mA MAX FUSED 10A MAX FUSED
PEAK MIN MAX 41/2 DIGITS 1 Second
41/2 DIGITS 1 Second
µ A
CAT II
Switch Box
V
+
AC Voltage
DC Voltage
III
87 TRUE RMS MULTIMETER III
iy2f.eps
Figure 2. Measuring AC and DC Voltage