SectionIII

bar or a large solid copper wire, and adjust AlR429 (Thermal Adj) for zero display. AlR429 is accessible through the rear panel.If the 3490A has the rear input connector, loosen the hinged cover to gain accessto

AlR429.

Be wre to connect the Guard Terminal and to observe the maximum voltage limitations noted on the front panel and in Table 3-1, or damage ta the instrument may rewlt.

3-42.DCSampleRateandResponseTime.

3-43. The samplerate and responsetime for dc voltage measurementsareshownin Table3-2.

Table 3-2. SampleRateand ResponseTime.

 

Minimum SamplePeriod*

Response

 

 

 

Function

Option 050

OptionO60

Time

DC Volts

2 4 0 . 2 m s + 5 m s

2 0 0 . 1m s + 4 m s

200.1ms

AC Volts

1 . 2 6 s + . 0 2 5 s

1 . 0 5 s + . 0 2 5 s

1 . 0 5s

Ohms

 

 

 

.1 k thru

 

2 0 0 . 1m s + 4 m s

2OO.1ms

100ko

2 4 0 . 2 m s + 5 m s

1,O00kf,,

3 0 0 . 2 m s + 6 m s

2 5 0 . 1m s + 5 m s

ms

25O.1

10,000ko

660.3ms+ 12 ms

550.2ms+ l0 ms

550.2ms

*Sample Rate Control set to FAST position and instrument not in overload. Each counterclockwise step adds 240 ms in Option 050 instruments,200 ms in Option 060 instruments.

3-44. Input Resistance.

345.Input resistancein the dc function is greaterthan 101o ohms on the .1 V, I V, and 10V ranges,and l0 megohmst 0.15 7oon the 100V and 1000V ranges.

3.46.ACVOLTAGEMEASUREMENTS.

Be sure to connect the Guard Terminal and to observe the maximum voltage limL tations noted on the front panel and in Table 3-1, or damage to the instrument may result, and high frequency measurements will be in enor-

341 . The display will NOT rcad zero on any ac range with the input shorted.The indicationon all rangeswith the input shorted should be less than 50 counts. The accuracyof ac measurementsbelow 1.0%of full rangeis not specified.

3-48.ACSampleRateandResponseTime.-3-49.The samplerate and responsetime for ac voltage measurementsareshownnTable 3-2.

Model3490A

3-50.FrequencyBange.

3-51. Frequencyrangeof the ac converteris 20Hz to 250kHz, r"itft u maximum volt-Hertz product of 107. That is, the frequencyrangefor the I V and l0 V ranges is 2OHz to 250 kHz, but the maximum frequency at 100V is 100kHz, andat 1000V it is l0 kHz.

3-52. Input lmpedance.

3-53. Input impedancein the ac function is the sameon all ranges,and is 2 MO t I % in panllel with ( 65 pF in instruments without rear panel input and (90pF in instrumentshavingtire rearpanelinput connector'

3-54.HarmonicDistortion.

3-55. The 3490A has an average-respondingac-dccon-verter circuit calibrated to display the rms value of a sinusoidalinput. Therefore,any distortion presentin the input signal will affect the accuracy of the measurements asshownin Table3-3.

Table3-3. Distortion Error.

 

 

YoError

 

 

{*Fundamental)

Harmonic

% Distortion

 

 

 

 

M a x .

M a x .

 

 

Positive

Negativr

Any

o . 1

0.000

 

even

0 . 5

0.001

 

 

1 . 0

0.005

 

 

2.O

0.020

 

Third

0 . 1

o.033

0.003

 

o . 5

0.168

o.167

 

1 . 0

0.338

0.328

 

2 . o

0.687

0.667

Fifth

0 . 1

0.020

0.020

 

o.5

0 . 101

o.099

 

1 . 0

0.205

0.195

 

2.O

o.420

1.380

*Depends on phaserelationship between harmonic and fundamental.

3.56.RESISTANCEMEASUREMENTS.3-57. When the 3490A is making resistancemeasure-

ments, movement of the instruction card will cause display readingsto jump. For optimum accuracy of mtusur.*ents on the .1 kO range'first set Rangeand Function to .1V dc, short the input terminalswith a copper bar or large solid copper wire, and adjust efn+zq (Thermal Adj) for zero display'A1R429 is accessiblethrough the rear panel.If the 3490A has the rear input connector, loosen the hinged cover to gain

accessto the adiustment.