Model3490A

STEPINPUT

-F U L L SCALE

SAMPLE/HOLD

T R I G G E R

APERTURETIME>

ACOUISITIONTIME

Figure3-15. Measurementof a StepInput.

The step input voltagemust remain stablefor at leastthe duration of the Acquire/Hold aperature time shown in Table 1-2.

3181. MeasuringPulse Height. hcquire/Hold may be used to measure the height of a pulse or squarewave. The width of the pulse (or one-half of the squarewave) must be greater than the aperture time shown in Table l-2. Triggering may be applied coincident with the leadingedgeof eachinput pulse.

3-182Using.50Hz or 60Hz PowerSource(Options 050or060).

3-183. The 3490A has the capabilityof operatingfrom a 50 Hz or 60 Hz power source.Option 050 is available

for 50 Hz operation and consistsof usinga 3.333 MHz crystal(Y2) in the clock and AlR207 = 100 kSr.Option 060 provides for 60 Hz operation and usesa 4 MHz crys-

tal CYI) in the clock and AlR207 = 84.5 kQ. SeeTable 2-1.

$184.RATIOlf'leasurements(0ption080).

3185. Instructionsfor makingratio measurementswith

the Model 3490A, Option 080, are contained in the following paragaphs. DC-to-dc and ac-to-dc ..three-

wire" ratio measurementscan be made;that is, the EXT REF input Low terminal and the INPUT Low terminal are connectedintemally. Becausethe sameterminalsare

used for Ohms measurementsand for Ratio measure- ments, thesetwo functions aremutually exclusive.

$186.ExternalBeferenceVoltages.

3187. The front panel Ratio switch selectseither the lntemal Referenceor the I V or l0 V External Reference range. If the I V range is selected,the external

SectionIII

Figure3-16. RatioInput Connections.

reference voltage may be either a positive or negative voltagebetween0.1 V and 1.2Y. On the l0 V range,the referencemay be positiveor negative,I V to l2 V.

3-188lnput.Connections

3-189. The dc external referenceand unknown input voltageshouldbe connectedasshownin Fizure3-16.

Extemal Reference Low and Input Low must be at the same potential; these terminals are connected intemally. Connect Guard to Input Low.

3-190Ratio.Display.

3-191. Ifthe I V External Referencerangeis selected, the display reads the ratio directly, but if the 10 V referencerangeis used,multiply the displayby 0.1. In dc/dc ratio measurements,the polarity symbol is + vshsn the external reference and input voltagesare the same polarity, and - if they are oppositein polarity (seeTable 3-ll). In ac/dc measurements,no polarity symbol is displayed.Any ratio measurementis limited to l2O % of

the input range selected. If autoranging is selected, 'upranging

occurs at l2O % of rcngeand downrangingat lO% of range. Overloadindication is the same as in voltagemeasurements.

Table3-11. Ratio PolarityDisplay.

External

 

 

Reference

Input

Displayed

I nput

Signal

Polarity

+

+

+

+

 

 

 

+

 

 

 

+

+ac none

ac none

3-192. RatioMeasrementProcedure.

a.Set RATIO switch to I V or l0 V EXT REF range.If the externalreferencevoltageis between1.0V

3-21

tu