Model3490A

Be sure to connect the Guord Terminal and to obserye the maximum voltage limitations noted on the front panel and in Table 3-1, or damage to the instrument may result.

3-58.InputConnections

3-59. Figure 3-3 shows the proper connections for making resistancemeasurements.All four terminals must be connected, since there is no internal connection between O Signal Low and Input Low. Maximum total O Signallead resistancepermissibleis 10 O.

O S I G N A L

Figure3-3. Ohmmeterlnput Connections.3-60.0hmsSignalVoltageandCurrent.

3-61. The maximum voltage acrossthe resistancebeing measuredis 13 V for valid measurementsand 25 V in overload. Table 3-4 lists the approdmate short circuit current for each range. Accurate voltage and current sourcesare not required,sincea resistancemeasurement is the ratio of the voltageacrossthe unknown resistance as a result of the reference current, to the reference voltage which determinesthe amount of the currenr.

Table34. OhmmeterCurrent.

 

Nominal

Range

Current

.l ko

1 m A

l k o

l m A

10 ko

l m A

100 ko

1 0 p A

1,000ko

1 0 p A

10,000ka

1 ttA

3-62.0hmmeterSampteRateandBesponseTime.3_-63.Ohmmetersample rates and responsetimes are shownin Table3-2.3-64.EXTERNALTRtcGER(Option020).

365.The BCD/Remote Expand Option 020 adds the capability of remotely rriggering the 3490A through either the Data Output or Remote Input connector.In order to remotely trigger the instrument, the Sample

SectionIII

Rate control must be set to Hold, or a continuousLow signalappliedto the Hold connectionat either rearpanel connector.The External Encode signallogic levelsand timing requirements are shown in Figure 34. The High to Low transition of ExternalEncodeandData Flaecan occursimultaneously.

HOLD

Pilä:::",----__1_ r

EXTERNAL,

ENCODE o

34904.81&

Tl - External Encode must be HtLiH at teast 16 ps before Data Flag goes LOW. This requirement rnay be met by changing External Encode to HIGH immediately after Data Flag goes HIGH indicating the start of a measurement sequenoe.

T2-ExternalEncode müSt be HIGH for at least 4gps before it goes Low to initiate a measurement. lf External Enmde was set HtGH immediately after Data Flag went HIGH, the T2 requirement rnay be met by holding External Encode HIGH until Data Flag goes LOW indicating completion of a measurement sequence.

T3 - External Encode must rernain LOW for at least 24O ps to be accepted and initiate a rEasurement.

T4 - Data Flag will go HIGH within 230 ps of receipt of a valid HIGH to LOW transition of External Enc,ode.

Figure3-4. ExternalTriggerSequence(Option 020).3-66.DATA0UTPUT(Option021).

3-67. The Data Output option providesten columnsof measurementdata, including polarity, range,function, and overloadinformation. A Data Flag(prini Commandj output is also provided, as are inputs for printer hold

and triggering. Figure 2-5 shows the Data Output

. connectorand signalsA. matingconnector,-hp part No. ". 1251-0086(Amphenol No. 57-30500-375)is supptied with Option 021. A cable terminated at each.nä'byu 50-pinconnector,-hp-562A-16C,is availablefor con-

nection to -hp-digitalrecorders.3-68.OutputSignalsandLevels.

3-69. If the Model 3490{is equippedwith Data Output Option 02l ,Ien columnsof l-24-8 codedBCDinformation are provided,In addition to 6 columnsof measurement magnitudeinformation, range,function, polarity, and overloadinformation are provided.The logic HIGH level= + 3.9 V r 1.5V, 400 pA max. The LOW level =0.3V + 0.3V, l5mA max. ColumnsI through 6 print the numericalmagnitudeof a measurementFigure. 2-5shows the print code for columns 7 through 10, using a standard -hp-print wheel, + or - 124g. The HIGH/LOW switch on the Outguard Data Output Assembly,Al0, must be set to correspondto the logic true level required by the digital recorderused.Figure 3-5 showsthe printout for Option 021.

3-5