Fluke 8021B Instruction Manual page 34

8021
1.
DC
VOLTAGE MEASUREMENTS
Loading
Error
in
% =
100
x
Rs-f (Rs
+-10 7
)
Where: Rs
=
Source
resistance
in
ohms
of
circuit
being
measured.
2.
AC
VOLTAGE MEASUREMENTS
First,
determine input impedance, as
follows:
'
Z
in
=
Where:
Zin
=
effective input
impedance
Rin
=
10
7
ohms
Cin
=
100
x
10
-
'
2 Farads
F
=
frequency
in
Hz
Then, determine source loading
error as follows:'
Zs
Loading
Error
in
%
=
100
x
Zs
+
Zin
Where: Zs
=
source impedance
Zin
=
input
impedance
(calculated)
* Vector algebra
required.
10
7
'1
4-
(2
7T
F Rin- C) 2
Figure
2-11.
Voltage
Measurement Error Calculations
(Loading Error)
2-37. Four ac and four dc current ranges are included on
the
802
i
B: 2
mA,
20
in
A, 200
mA
and 2000
mA.
Each range
is
diode
protected to 2
amps
and
fuse protected
above
2
amps.
If
a fuse blows, refer to fuse
check and replacement information given
earlier in
this
section.
2-38.
In
high
electrical
noise
environments
(near
ignition
switches, fiourescent
lights,
relay switches,
etc.)
unstable or erroneous readings (exceeding specifications)
may
occur.
The
effect
is
most obvious when measuring low
level
current
on
the 2
mA
range.
If
an
erratic or
erroneous reading
is
suspected, temporarily
jumper
the
V/n
connector to the
mA
connector. This
is
recommended
for the 2
mA
and 20
mA
ranges only.
CAUTION
To
avoid possible instrument
damage
and/or erroneous
measurements
remove
Ihe
temporary V/fi-to-mA jumper before attempting voltage or
resistance
measurements.
2-18