User manual

Front Panel Operation
2001-900-01 Rev. K/ August 2010 3-33
2. Highlight the desired mode and press ENTER.
NORMAL: This option is for normal current measuring,
where the meter is placed in series with the current path and
the voltage across an internal shunt resistor is measured. The
Specifications are derated by 50 ppm for currents over 0.5 A
because of the self-heating effects on the shunt resistor.
IN-CIRCUIT: In-circuit current is a calculation based on a
4-wire resistance measurement and a voltage measurement.
It is similar to an offset-compensated ohms reading.
A measurement overflow occurs for any of the following
conditions:
• The measured voltage exceeds |±200 mV|.
• The trace resistance is less than 1m or greater than
10.
• The in-circuit current is greater than 12 A.
The current in a low resistance conductor (e.g., a printed
circuit trace) can be measured without breaking the current
path. The Model 2001 can do this with a pair of Kelvin test
probes across the conductor. See Figure 3-12. The method
follows:
1. Using one set of the Kelvin probe tips, the instrument
sources a known current (I
SOURCE
) through the conductor
and simultaneously measures the resulting voltage
(V
MEAS1
) with the other set of probe tips:
or
2. The instrument then measures the voltage (V
MEAS2
)
across the conductor without sourcing an additional cur-
rent:
or
3. It then calculates the in-circuit current by combining the
equations and solving for I
IN-CKT
:
Because of accuracy considerations, in-circuit current
readings are limited to traces with a resistance of 1 m to
10 . If either of these limits is exceeded in the resistance
calculation, the in-circuit current cannot be calculated. The
bottom line of the front panel display will show and update
the trace resistance.
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DC in-circuit current measurements
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2001 MULTIMETER
SENSE
Ω 4 WIRE
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INPUTS
CAL
500V
PEAK
F
R
FRONT/REAR
2A 250V
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350V
PEAK
1100V
PEAK
Model 2001
Circuit
Under Test
Caution : Maximum Input = +200mV on (I
IN - CKT
+ I
SOURCE
) • R
TRACE
,
where I
SOURCE
= 10mA.
+00.207 ADC ICkt
Trace resistance: 1.0000Ω
Y
Y
x
Note: The distance
"X" must be greater
than 10 times the
distance "Y" or
additional errors will
be introduced.
V
MEAS1
I
IN-CKT
I
SOURCE
+R
TRACE
=
R
TRACE
V
MEAS1
I
IN-CKT
I
SOURCE
+
-------------------------------------------------=
V
MEAS2
I
IN-CKT
R
TRACE
=
R
TRACE
V
MEAS2
I
IN-CKT

----------------------=
V
MEAS1
I
IN-CKT
I
SOURCE
+
-------------------------------------------------
V
MEAS2
I
IN-CKT

----------------------=
V
MEAS1
I
IN-CKT
V
MEAS2
I
IN-CKT
I
SOURCE
+=
V
MEAS1
I
IN-CKT
-V
MEAS2
I
IN-CKT
V
MEAS2
I
SOURCE
=
I
IN-CKT
V
MEAS1
-V
MEAS2
=V
MEAS2
I
SOURCE

I
IN-CKT
V
MEAS2
I
SOURCE

V
MEAS1
-V
MEAS2

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