Section V

PERFORMANCECHECKS

Model3490A

the 3490A accuracy.In this case,a correction factor

chart should be used to adjust the calibrator output. -hp- '745A1746A

Such a chart for themay be derived during routine periodic calibration of the instrument, and can be used to set the 745A controls for a precise output. For example,if the 745A output is known to be 0.04% high at I V, 20H2, the 745A can be set for a precise 1 V output. by setting the 745A voltage set controls'to1.000000V and adjustingthe error measurement control to +0.04%. The corrected voltage will then be sufficiently accurateto test the 3490A at I V, 20H2. To determine the length of time that the correction factor chart will be valid, refer to the latest 745A1746AOperatingand ServiceManuals.

t.

5-13. To verify the ac voltageaccuracyof the 34904 at frequencies above I l0 kHz, the ac to dc transfer measurementtechnique may be employed. Using the test setup shown in Figure 5-1, apply an accuratedc voltage to the thermal converter and adjust the dc differential voltmeter for a null indication. Remove the dc input from the thermal converter and apply the ac signal to both the thermal converter and the 349OA input simultaneously.Adjust the test oscillator output level to return the differential voltmeter to a null indication. This results in an rms value of the ac signal equalto the rms valueof the dc standardoutput.

5-14. Table 5-3 lists the voltageand frequency points which should be checked to verify the ac voltage accuracy of the 349OA, together with the test equipment neededfor eachcheck.If the equipmentrequired for some checksis not available,a good indication of performancecanstill be obtainedby checkingthe points

for which suitableequipment is available.

r-..

t-,,,-----l ( O ) @ u o

@ \ : d o - o o o

Connect Guard to Input Low or damageto the instrument may result.

5 . 15OHMMETER.ACCURACYTESTS .5-l6. PreferredMethod.

5-17. A resistancedecadewith settingsfrom 100Oto

10 MO is requiredfor this test.A correctionfactor chart for the decade is necessary to achieve the accuracy

required to check the performance of the 34904 'Ohmmeter function. Select the 3490A ranges and

resistancedecade settings shown in Table 54. The algebraicsum of the 34904 readingand the resistance decadeerror indicated by the correction factor chart should be within the limits given for each setting listed.

5-l 8. AlternateMethod.

5-19. If a suitableresistancedecadewith an appropriate correction factor chart is not available,resistorswithin the valuesshown in Table 5-5, whosevalueis known to within the tolerancesgiven, may be used to check performance of the 3490A ohmmeter function. The 3490A display should be within the number of counts shownfrom the valueof the resistorused.

5 . 20DC.COMMON - MODEREJECTIONTEST .

5-21. Effective common-moderejection is the ratio of the peak common-modevoltageto the resultanterror in

MULTIMETER h p 3 4 9 0 4

o @ o o @

DC OIFFERENTIAL VOLTMETER/ RATIOMETER

h p 5 4 2 O 8

OUTPUT

C A E L E

Figure5-1. AC VoltmeterHighFrequencyAccuracyTest.