Keithley 2002, User Manual, Page: 44 / 366

Front Panel Operation
2-27
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 read-
ings are limited to traces with a resistance of 1m
Ω
to 10
Ω
. If
either of these limits is exceeded in the resistance calcula-
tion, the in-circuit current cannot be calculated. The bottom
line of the front panel display will show and update the trace
resistance.
A procedure to measure in-circuit current follows:
1. Select the in-circuit current measurement mode from the
CONFIGURE DCI menu and place the instrument in
the DCI function. Note that the 4W annunciator lights to
indicate this is a 4-wire measurement.
2. Connect a set of Kelvin test probes, such as Keithley
Model 5805 or 5806, to the Model 2002 INPUT HI and
LO terminals and SENSE HI and LO terminals.
3. For R
TRACE
<50m
Ω
, or where the conductors are physi-
cally hot, rel out (zero correct) any thermal offsets that
are present before measuring in-circuit current. With
power to the test circuit removed, place the probes on
the desired trace and enable rel from the DCI function.
4. Turn on the power to the test circuit and read the in-
circuit current calculation. The speed of this
measurement is four readings per second at 1PLC. Its
range is fixed at 12A. The default filter for in-circuit
current is a moving average of ten readings. Additional
filtering may be needed at low current levels.
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
( )
+ =
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
( )
----------------------------------------------- =
A measurement overflow occurs for any of the following
conditions:
• The measured voltage exceeds |±200mV|.
• The trace resistance is less than 1m
Ω
or greater than
10
Ω
.
• The in-circuit current is greater than 12A.
COUPLING
This parameter selects the input coupling for the ACI
function.
AC:
With AC coupling selected, a DC block capacitor is
placed in series with the AC measurement circuit (note that
the current shunt resistors are always DC coupled to the
inputs. This removes the DC component from the RMS and
average ACI measurement.
AC+DC:
When AC+DC coupling is selected, the blocking
capacitor is removed. Subsequent RMS or average ACI
measurements reflect both the AC and DC components of the
signal.
Note that the coupling settings for ACI and ACV are discrete.
Thus, setting the coupling of ACI has no effect on the cou-
pling of ACV.
AC-TYPE
This parameter selects the measurement type for the ACI
function. The Model 2002 directly measures RMS and aver-
age AC current.
RMS: With this parameter selected, the instrument performs
RMS AC current measurements.
AVERAGE: When this item is selected, the signal path in
the instrument bypasses the RMS converter, and the average
ACI measurement is the filtered output of a full wave
rectifier.
Multiple displays
The multiple displays for AC current that show multiple
functions are shown in Figure 2-8. There are no multifunc-
tion displays for DC current.