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5700A/5720A Series II Calibrator
Service Manual
3-38
Note
The input impedance at INPUT 2 of the 5790A on the millivolt ranges is 10
M
Ω
shunted by 83 pF and the cable used to connect the shunt resistor to
the 5790A has 40 pF capacitance, for a total of 123 pF.
The reactance of 123 pF at 10 kHz is 129 kΩ, and using formula (1), in the case where
R=2 kΩ, the network impedance Z = 1.999760 kΩ. This produces an error of 120 PPM.
The allowable error at 10 kHz is reduced to account for this error.
Using formula (2) we get a result of Xc = 88 kΩ, and a network impedance of Z =
1.9995 kΩ. This produces an error of approximately 250 ppm, or 0.025%. However, if
we are making a measurement of 0.21% uncertainty (as in the present case), the ratio of
measurement uncertainty is about 10:1 and is not of concern. It is easy to improve
measurement uncertainty if desired, though, by measuring the actual input capacitance of
the detector and any stray capacitance from input leads, etc. and making corrections. In
this discussion, the UUT is assumed to be a high-impedance current source (like the
5700A), which can easily be verified by the manufacturer’s specifications, i.e., a
specified voltage adder for current outputs above a given burden voltage.
3-26. Wideband Frequency Accuracy Test
Use Table 3-30 for the test record. Proceed as follows to test the Wideband module
frequency accuracy:
1. Connect the Philips PM 6669 to the Calibrator wideband output and measure the
output frequency at the frequencies listed in Table 3-30.
2. Verify that the frequency counter indicates frequencies within the 0.01% limits
shown.
3-27. Wideband AC Voltage Module Output Verification
The wideband tests are for units with the Option 5700A-03 Wideband AC Module only.
The verification test for the wideband module works as follows:
• Accuracy at 1 kHz: Output at 1 kHz is tested by comparing the wideband output at
the end of the cable and termination supplied with the instrument to the 5790A at
INPUT 2.
• Attenuator flatness: The attenuator flatness is tested using the 5790A wideband input
and using reduced spec limits when the TUR (Test Uncertainty Ratio) is less than
4:1.
Table 3-11 lists the equipment required for testing and calibrating the Wideband module.