Slower sweep speeds produceslower readings
The Delta Time function
measures
the actual time co\'ered by
the intensified
area
of the CRT beam. The displa)' updates ever)'
third s
.....
eep.
At
higher sy,;eep speeds, the display updates
at
a
constant
rate
determined by tbe microcomputer processing
time.
At
lo
.....
er
s
.....
eepspeeds, ho
.....
e\·er. you may notice a slightly
slower update time
as
the microcomputer must wait for the end
of
~
s
.....
eepsto pnxluce
accurate
readings.
Measuring
rue
time
or
fon
time
Rise
or
fall time is
the
amount of time it
Lakes
a
.....
aveform to
change from
1000
to
90%
amplitude. The Delta Time function is
used v.itb the special markings on the left side of the CRT
to
measure
rise
or
fall time, The wa\'eform is adjusted until it
just
fills the CRT from the
0%
to the
100%
marks.
and
the Delta
Bar
is then adjusted to
CO\'er
tbe
area
from
10%
to
90%.
To measure rise time:
1. Adjust the
VOL
TSIDIVISION switch VERTICAL POSITION
control
and
vertical vernier conteol until the
.....
aveform extends
between the
0%
and
100%
CRT markings.
2.
Press
the
lJ.
TIME bulton.
3.
Adjust the ABEGIN and
lJ.E~'D
controls until the Delta
Bar
covers the portion
of
the
.....
aveform between tbe
10$
and
90$
marks
(the
dotted lineson theCRT screen).
"'.
Readthe rise timefrom thedigital display.
.
..
•
(
(
t.I
DEI
•
.-
:-.:..
..
Fig,
58 - To measure risetime, Intensify the area from
'0
to
90
on the
CRT
with the waveform extending from 0 to
100.
To
measure
faU
time:
The procedures
are
the
same
as
measuring rise time except the
Delta
Bar
is
usedto highlitethe falling
edgeof
thesignal.
Using
the
Delta
functions
to
measure
frequenC3/
The 1/
lJ.TIME
function calculates the equi\'alent frequency of
any signal
based on the period of one of its cycles. The applica·
tions of
this function
are
different than the frequency functions
covered
earlier
because the resulting frequency reading is only
an
approximation
based
on the period
of
one c)'cle.
It
is. there-
fore,
less
aceurate
than using the frequenc)' function on a
periodic signal.such
as
a sine
.....
ave
or
square
.....
ave.
The main application of the
11
ATIME function
is
to determine
39
the approximate frequency
of
a signal
that
is
part
of
some other
signal. such
as
interference. The results
are
faster
and
more
accurate
than making a frequency
measurement
using analog
oscilloscope procedures because there
are
fey,;er
chances
of
introducing interpretation
error
into the calculations. The test
is.
ho
.....
ever. based on the
same
concept
of
measuring a time
period to
calculate frequency. The microcomputer simply
dhides
the lJ.Time results into ··one" to pnxluce the I/lJ.TDoIE
reading.
The
accuracy
of the results
depends
on
how closely the Delta
Time
Bar
can
beset
tocoverexactlyone cycle
of
the signal.This
requires
estimating thebeginning and end
of
thewaveform to be
measured.
When
measuring a sinewa\·e. for example. it is
generally
easier
to
adjust
the Delta Measurement
Bar
from one
peak of
thesignal to the folloy,ing peak than it is to approximate
the
midpoint. Both methods
are
shown
in
Fig.
59
for comparison.
Fig.
59 - n is usualfy
easier
to mark the waveform from
one peak to the next (B) than to try to accurately estimate
the midpoints when meBsurinf/ equivalent frequency.
It
is
often
easier
to
measure
the period of two c)·cles.
and
then
multiply
the resulting frequency by two. on fast signals. This is
especially
true
if
the signal being measured has a frequency
O\'er
20
MHz.
or
if the period of the signal is very small
compared to the time of one
c)'cle
of
the main waveform.
Remember
that
~
..
ou multipl)' the resulting frequency by two
because having
the period ty,;ce
as
long results in a calculated
frequency
that
is
one-half the correct frequency.
To
measure
tbefrequency of a signal v.;th tbe Delta function:
1.
Expand thelocked w3\'eform until the detail of
the
signal to
be
measured
can
beseen
on
theCRT,
2..
Press
the
l/
1I.
TL\1E button.
3.
Adjust the lJ.BEGIX and 6
E~l)
controls until the intensified
Delta
Bar
exactlycoversone cycleof thesignaL
-I. Read the equivalent frequency from thedigital display.
NOTE:
The display
annunciators
indicate
.....
hether
the
results
are
in
H:. KH:.
or
MH:. The decimal is
always
correctly
placed
by the microcomputer for the displayed
range.
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