protected above 2 amps. If the fuse blows, refer to
fuse replacement information given earlier in this
section.
2
-
31a. In high electrical noise environments (near
ignition systems, fluorescent 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/kfl/nS connector to the mA connector. This will
ensure an accurate measurement.
CAUTION
To avold possible Instrument damage
and/or
erroneous measurements remove the
temporary
V/kn/nS-to-mA Jumper before
attempting voitage or resistance measure
-
ments.
WARNING
instrument damage and operator injury may
result if the fuse
blows while current is being
measured In a clrcult which exhibits an open
circult voitage
>250 volts. To prevent this
possibility, place a suitable mounted and
insulated 1.5A fuse of the proper voitage
rating
(>250V) in serles wlth the high (mA)
input lead.
2
-
32.
Full scale burden voltage (voltage drop across
the fuse and current shunt) for all ranges except 2000
mA
is less than 250 mV. The 2000 mA range has a full scale
burden voltage of less than 700
mV. These voltage drops
can affect the accuracy of a current measurement, if the
current source is unregulated and the shunt plus fuse
resistance represents a significant portion
(11 1000 or
more) of the source resistance. If burden voltage does
present a problem, the percentage of error can be
calculated using the formula in Figure 2
-
4. This error can
be minimized by using the highest current range that
gives the necessary resolution. For example, if 20
mA is
measured on the 2000
mA range the burden voltage is
approximately 5
mV.
2
-
33.
Conductance
2
-
34. The conductance ranges, 200 nS and 2 mS,
are included on the 8020A for making both conductance
and resistance measurements. When either range is
selected the display reads the measurement results in
terms of conductance
(]/a). If resistance readings are
required, refer to the conductance
-
to
-
resistance
conversion information given in Figure 2
-
5.
AMMETER SHUNT
ES
=
Source voltage
RL
=
Load resistance
+
Source resistance
IM
=
Measured current (display reading in amps)
EB
=
Burden voltage (calculated), i.e.
Display reading expressed as a
%
of full scale (100 x
]times full scale burden voltage for
FULL SCALE
selected range. See table.
RANGE
F.S.
BURDEN VOLTAGE
2
mA to 200 mA
0.25V
2000 mA
Current error due
to
Burden Voltage
IN AMPS
=
EB IM
E~- E~
Example: ES
=
14V. RL
=
9R,
IM
=
1.497A.
497
x 0.7 (from Table)
=
EB
=
100
X-
2000
74.9%
of
0.7
=
0.524V
Error in
%
=
100
.524
=
.524
=
100
14-.524 13.48
3.89%
Increase displayed current by 3.89% to
obtain true current.
.524 x 1.497 .784
Error in amps
=
-
-
--
-
.058A
14-.524 13.48
increase displayed current by
0.058A to
obtain true current
2
-
35.
The 200
nS range is intended for use in making
Figure
2-4.
Current Measurement Error
fast, accurate, high
-
resistance measurements from
5
Mfl
Calculatlons
To Next Page
Loading...
