Current Measurement Accuracy Limits - Keithley SourceMeter 3A 2420 Service Manual

1-14 Performance Verification
3A range accuracy
NOTE
1.
2.
3.
4.
NOTE
5.
6.
NOTE
Table 1-6

Current measurement accuracy limits

Model 2420 source
and measure range*
*Measure range coupled to source range when simultaneously sourcing and measuring current.
**As measured by precision digital multimeter. Use closest possible value, and modify reading limits
accordingly if necessary.
***Current calculated as follows: I = V/R, where V is the DMM voltage reading, and R is the character-
ized value of the 1Ω resistor.
The 1 Ω resistor should be characterized to within ±300ppm before verifying the 3A
current measurement range. Use the 4-wire ohms function of the DMM to measure the
resistance value, and then use that measured value to calculate the current during the
measurement procedure.
With the power off, connect the 1Ω resistor and digital multimeter to the Model 2420
INPUT/OUTPUT jacks, as shown in Figure 1-3.
Select the multimeter DC volts function.
Set the Model 2420 to both source and measure current by pressing the SOURCE I and
MEAS I keys, and make sure the source output is turned on.
Verify measurement current accuracy for the 3A range as follows:
• Select the 3A source range.
• Set the Model 2420 source output to the correct 3A value as measured by the digital
multimeter.
• Note the DMM voltage reading, and then calculate the current from the voltage reading
and characterized 1Ω resistance value as I = V/R, where V is the DMM voltage reading
and R is the characterized resistance value.
• Verify that the Model 2420 current reading is within the 3A limits given in the Table 1-6.
It may not be possible to set the current source to the specified 3A value. Use the clos-
est possible setting, and modify reading limits accordingly.
Repeat the procedure for a negative 3A current.
Repeat the procedure using the rear panel INPUT/OUTPUT jacks. Be sure to select the
rear panel jacks with the front panel TERMINALS key.
Test currents above 105mA cannot be maintained longer than 1 minute without
affecting accuracy. See derating information in Note 1 under Table 1-5.
Source current**
10µA 10.00000µA
100µA 100.000µA
1mA 1.00000mA
10mA 10.0000mA
100mA 100.000mA
1A 1.00000A
3A 3.00000A
Model 2420 current reading limits (1
year, 18°C-28°C)
9.9966 to 10.0034µA
99.969 to 100.031µA
0.99967 to 1.00033mA
9.9959 to 10.0041mA
99.939 to 100.061mA
0.99883 to 1.00117A
2.99673 to 3.00327A***