HP Car 3490A manual Tnputvoltageat, M Eo F S / Ht R I G G E R, Voltageactually, Measured

Model3490A SectionIII

TNPUTVOLTAGEAT

T I M EO F S / HT R I G G E R ,

VOLTAGEACTUALLY

tMEASURED .

/l

/l

I

I

I

I A r

A = ANALOG DELAY

T= SAMPLE/HOLDTRIGGER(TRACK/HOLDMODE) V = VOLTAGEMEASURED

S = SLOPE,SEEPARAGRAPH3 - 12FORMAXIMUMSLOPEPERMISSIBLE .

Figure3-12. Digitizinga Ramp.

shown in Table l-2 under the "Time ResponseChara- cteristics" heading. The shorter the time between mea- surement points, the greater the accuracyof the recon- structed waveform will be.

3-176. Digitizing a Sine Wave. The rules that apply

when-digitizing a ramp @aragraph3-174) also apply to measurement of a sine wave. Keep in mind that the

dV/dt and frequency limits givenin Paragraph3-158 and Table 3{ must be observed. The waveform may be reconstructed from the Track/Hold measurementinfor- mation asdiscussedin Paragraph3-175.

3-177. Ramp Linearity MeasurementAided by an Oscil- loscope. An oscilloscope with delayed sweep and a delayed gate output can be very helpful in making Sample/Hold measurementsof a repetitive waveform. For example, linearity of a ramp can be measured accurately,asin the following procedure.

a.Choosean oscilloscopewith delayedsweep,such as the {rp- Model l80C with the l82lA Time Base/ Delay Generator plug-in unit. Be sure the Delayed Gate output from the oscilloscopemeets the Sample/Hold

Tdry:. input signal requirements given in päragraph 3-l 60.

b.Connect the Delayed Gate output from the oscilloscopeto the S/H AC Triggerinput. lf the 3490A

has Option 020 installed, connect the S/H Stretched Pulse Output to the External Encode input (see Para- graph3-170).

c. Connect both the Main Gate and Delayed Gate

outputs from the oscilloscopeto an interval timer (such as the -hp-Model5300Al53O2A)to determinethe delay

time accurately.

d.Connect the ramp sigral to be measuredto both the 3490A input and the oscilloscopeverticalinput. The slope of the ramp must be within the limits given in Paragraph3-158 and Table 3-8. Triggerthe oscilloscope main sweepat the beginningof the ramp.

e.Set the SampleiHold control to TrackiHold. The measurementwill then be triggered at the point where the delayed-sweepintensified trace appears along the ramp.

f.Positionthe delayed-sweepintensifiedtraceat any number of sampling points (at least three) along the ramp,asshownin Figure3-13.

g.The slope of the ramp betweenvariousmeasure- ment points can then be compared to determine linearity. ln Figure 3-13, for example,slopeAB should be comparedto slopeBC asfollows:

3-r9