Calibration and Verification
Performance Verification Tests
3
3-51
Loop Until (Len(response) <> 0)
capdata(x) = Val(response)
Print #CapChan, Val(response)
Next x
Close #CapChan
’ throw out first and last reading, compute delta v
deltav = capdata(no_samples - 1) - capdata(2)
’ dci() is the current; multiply by the charge time and divide product by change in
voltage
’ charge time is (10 seconds - 2*100mS samples - 100mS for 0th sample)
result = (dci(stp) * 9.7) / deltav
End Sub
Figure 3-19. Example Visual Basic Program (cont)
3-29. Measurement Uncertainty
An example of how to compute measurement uncertainty for a 3 mF verification is
shown below.
Error Analysis Example: 3 mF tested at 800
A
• 5700A DCI, 2.0 mA range: 50 ppm + 10 nA; at 800
A: 62.5 ppm.
• HP 3458A DCV, 10 V range: 4.1 ppm of reading + 0.05 ppm of range.
• HP 3458A time base uncertainty: 100 ppm.
• UUT (Fluke 5520A) 3.0 mF: 0.44%
While the HP 3458A dc volts accuracy is not specified for sample rates other than NPLC
of 100, Fluke testing indicates the DMM is within 25 ppm for the fast sample rate.
Adding the error terms yields (62.5 ppm + 25 ppm + 100 ppm) = 187.5 ppm, or 0.0187%,
for a test uncertainty ratio (TUR) > 20:1. The DMM has a number of other error sources:
linearity, uncertainty on the 10 V range at 2% of full scale, uncertainty in fast sample
mode and internal trigger timing uncertainty are all of concern. Furthermore, the current
source accuracy is not independent of the continuously changing compliance voltage.
Fluke tests were performed to quantify each of these error sources, and none were found
to contribute more than 0.02%. This is not significant relative to the 5520A capacitance
verification. See Table 3-28 in this chapter for capacitance verification tests.
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