Agilent Technologies 34411A Especificações descarregar pdf (Página 10)

The 34411A level trigger is

specified in units of any mea-

surement function. In this case,

a DCV measurement is being

made at 50 k samples/s. With

1 million readings, 20 seconds

of data can be stored at this

rate. Pre- and post-triggering

allows you to create a scope-

like capture of the waveform

around an event. The DMM will

continuously make measurements

until the level trigger is met. It

will retain the pre-trigger count

of measurements and then begin

the count of post-trigger mea-

surements. This is an excellent

alternative to waiting for an

asynchronous event, and there

is no discontinuity of measure-

ments between pre- and post-

trigger counts.

Delayed sampling from occur-

rence of an external trigger

In many applications, you need

to wait a period of time before

actually making a measurement,

as illustrated in the example

where we discussed precision

DC measurements of pulses.

There are many reasons for

delaying a measurement. You

may need to wait for the signal

to settle – as is typical when

you are measuring large resis-

tances in the presence of stray

capacitance. In the ballast

application we discussed earlier,

a delay is needed to make the

instrument wait until after the

initial high-voltage discharge

has taken place, so the quies-

cent AC voltage level can be

measured.

Both the 34410A and 34411A

have a hardware-coupled

external trigger input. A delay

can be inserted between the

external event and the start

of any measurement. This

delay can be zero, and the

measurement engine starts its

measurement in less than 1 µs

from the external trigger (DC

measurement). The delay can

also be up to 3600 seconds

(with 20 µs resolution).

Both the 34410A and 34411A

have a precision sample timer

with very little jitter (<100 ns).

An external trigger event can

start a single measurement

or a burst of measurements

spaced by the sample timer.

Figure 5 illustrates the concept

of a separate trigger delay

and sample intervals. Sample

intervals can be as low at

100 µs for the 34410A and

20 µs for the 34411A.

10

Interval Interval Interval

Trigger

Trigger

Delay

Sample #1 Sample #2 Sample #3

Figure 5. Using a precision timer to sample signals

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 19 20

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