Model3490A

3-26.0verrangeMeasürements.

3-27. Measwementswithin rated accuracy are possible up to 120 7oof rungeon all except the 1000 Vac or dc ranges.Overrangeinputs on theserangeswould exceed the maximum allowable input voltage. The display includesthe overrange"1" asthe sixth digit.

3-28.OverloadIndication.

3-29. lf the measurementis 120% of nnge or geater, the Overload "OL" annunciator will light. The numerical displaywill read 120000to 120005.

3-30.BangeIndication.

3-31. The 349OA display always reads in volts or kilohms (except in Ratio measurements), with the decimal point and range switch indicating the range selected. In autorange mode, the decimal point alone indicatesrange.

3-32.FunctionIndication.

3-33. In the standard 3490A, function is indicated only by the function switch position. If optional Remote control is in use, the "REM" annunciator lights to indicate that the front panel switches are disabled.An available special display assemblyadds V, AC, Kfl and TST annunciatorsto indicate the function selected.

3-34.Autoranging.

3-35. In the autorangemode,uprangingoccursat l2O% of rangeand downranglngat lOVoof range.Ameasure- ment sequenceis not completed unlessthe readingis on the proper range. For example, if the Sample Rate control is set to Hold and the Manual Trigger pushbutton depressedonce, the 3490A will continue to sampleuntil one readingis taken on the correct range. When the 3490A is changedto the autorangemode from a voltage range, the first reading in autorange is not valid.

3-36.ManualTrigger.

3-37.Manual triggering is availableon all instruments. When the Sample Rate control is set to Hold, one measurementresultseachtime the Manualpushbutton is depressed.If the pushbutton is depressedwhile the instrument is not in the Hold condition, automatic samplingwill stop until the button is released.

3.38.SELF.TESTOPERATION.

3-39. The Intemal Test function of the 3490A verifies proper operation of most of the dc circuits, logic circuits, and the ohmmeter reference.Use the following procedureto perform the Intemal Tests.If TestNo. I ii

not correct, refer to the TroubleshootingsectionIfany.

of the other tests are not correct, refei to the perfoi_ manceChecks.

SectionIII

a.Set Function to TEST. If instrument has Ratio or Sample/Hold options, set RATIO to INT REF and SAMPLE/HOLDto OFF.

b.Set SAMPLE RATE control one position clock- wise from HOLD.

c.Select RANGE l, which is Logic Test. The display

should _followthe sequencebelow, starting at any point in the list. All readings should be in the order ih-own,

with the polarity sign, numbers, and decimal points ai shown. The last reading listed displays all digiis as the count accumulates, then stops at the number shown. The,last two digits in the last number arenot significant to the test. If these displaysare correct, most of the logic circuits areoperating correctly.

+080.024

+o4.oo24+0.20024+.0too24+0.09032+to.oo24+200.024+4000.24+80002.4+6000.xxOL

d.SelectRANGE2. Thedisplayshouldbe .000000 t 2 countsThis.verifiesthe l0 V rangezero.

e.SelectRANGE 3. Differencebetween+ and - readingsshouldbe (8 counts.

f.SelectRANGE4. Usinga dc standardhavingan accuracyof t 0.01% or better, apply an input of

-10.0000V. Displayshouldbe + 09.9990+ (16 counts

+dc standarderror).Thischecksthe+ ReferenceIfthe. 3490A hasthe ratio option,set RATIO to EXT REF l0 V and short EXT REF input terminals.Display shoüldbe r 00.0000.This checksthe Ratio Reference

dmplifier zero. Return RATIO switch to INT REF positionandremoveshortfrominput.g. SelectRANGE5. Displayshouldbe000.000t t5 'counts,verifyingthe0.1V rangezero.

h.SelectRANGE 6. Usinga dc standardhavingan accuracyof t 0.01% or better, apply an input of

-10.0000V.Displayshouldbe - 1000.00I (35 counts

+dc standarderror). This ehecksthe dc input 0.01 attenuationandthedcamplifierxl00 gain.

i.SelectRANGE 7. Short fl SIGNAL terminals. Dsplayshouldbe- 09700.01 7000countsThis.verifies properoperationof theOhmsConverter.

3-40.DCVOLTAGEMEASUREMENTS.341.For optimum accuracyof measurementson the.l V range,first shorttheinput terminalswith a copper

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