Keithley SourceMeter 2425, Руководство по обслуживанию

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Model 2425 Service Manual Performance Verification 1-5
1
Ω
resistor characterization
The recommended 1
Ω
resistor should be characterized to ±300ppm or better before veri-
fying the 3A current measurement range. (You need not characterize the resistor if you are
checking only the 3A current source range.) Use the 4-wire ohms function of the DMM
recommended in Table 1-1 to measure the resistance value. Then use that measured value
to calculate the current during the 3A current measurement range test procedure.
Verification limits
The verification limits stated in this section have been calculated using only the Model
2425 one-year accuracy specifications, and they do not include test equipment uncer-
tainty. If a particular measurement falls outside the allowable range, recalculate new limits
based on Model 2425 specifications and corresponding test equipment specifications.
Example limits calculation
As an example of how verification limits are calculated, assume you are testing the 20V
DC output range using a 20V output value. Using the Model 2425 20V range one-year
accuracy specification of ±(0.02% of 2.4mV offset), the calculated output limits
are:
Output limits = 20V ± [(20V
×
0.02%) + 2.4mV]
Output limits = 20V ± (0.004 + 0.0024)
Output limits = 20V ± 0.0064V
Output limits = 19.9936V to 20.0064V
Resistance limits calculation
When verifying the resistance measurement accuracy, it will probably be necessary to
recalculate resistance limits based on the actual calibrator resistance values. You can cal-
culate resistance reading limits in the same manner described above, but be sure to use the
actual calibrator resistance values and the Model 2425 normal accuracy specifications for
your calculations.
As an example, assume you are testing the 20k
Ω
range, and that the actual value of the
nominal 19k
Ω
calibrator resistor is 19.01k
Ω
. Using the Model 2425 20k
Ω
range one-year
normal accuracy specifications of ±(0.063% of reading + 3
Ω
), the recalculated reading
limits are:
Reading limits = 19.01k
Ω
± [(19.01k
Ω ×
0.063%) + 3
Ω
]
Reading limits = 19.01k
Ω
±15
Ω
Reading limits = 18.9950k
Ω
to 19.0250k
Ω