8021
B
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
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