Tektronix 7000 Series Manual page 9

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. . .
. . .
.
. ι
.
the signal being measured, you have
, ., ,
_ _ _,
. . -
non-repetitive
nals, like gated bursts . As with time
interval measurements, the delayed
. display . -
sweep gate
. - oscilloscope . .
Intensified . .
.- . nvenient gating signal .
cates position of arming gate .
is generated each time the trigger an d
armi ng conditions are met. Α
t
h ird dis-
play, CH Β, is α conditio n ed signal that
6
is
d erived from the 7D15's C H Β trigger
circ uit . It is useful for setting up t h e
trigger conditions of chan nel Β.
Counter Gate Displays . B oth
t
h e 7D14
and the 7D15 provi de the ca pability of
displaying their internal measurement
interva l
gates,
w
h
ic
h
indicate th e
ac-
tual points of α meas urement. As is
shown in Fig . 2, these gates are
d
iffer-
ent from t he external or arming gates.
The counter gate
d is p lays
h
el p to re-
duce errors, s pee d set up time, and
provide you with greater trigger selec-
Selectable Resolution an d Accuracy .
tivity . Measurement averaging and selectable
Wh en the 7D14 an d 7D15 are in vertical
cloc k rates on the 7D15 allow you to
mainframe compartments, t h e gate d
select the amount of resolution an d th e
d is p lays are obtained by
p
ressing the
maxim u m accuracy possible fo r α par-
app ro priate main frame c hannel selec-
ticula r time meas ur ement. Th is feat u re
tion switch. In α
h
orizontal compart-
also
h
el ps you
p
revent readout over-
me nt, α ca ble m ust
b
e connecte d from
flow when measuring long time inter-
either the M ON ITO R co nn ector (7D14)
vals .
or the DISPL AY ED WAVEFORM OU T-
The CLOC K
p us h buttons set th e basic
PUT connector (7D15) to o n e channel resolution of the counter . Th e 7D15's
of α vertical am plifier. Wh en the coun- fastest cloc k rate is 10 ns, whic h is the
ter gate is
d is p laye d (see Fig . 2), you maximum resolution
p
ossible for α
can see the signal being measured single shot time measurement. Wh en
along with
t he actual i n terval in wh ic h measuring re petitive signals, resolution
th e meas u rement is being ta k en . Th e can be increase d using measurement
arming gate is generally not
d
isplayed.
averagi ng .
M
easu rement averaging is α
H
owever, if the
d
elayed swee p gate is
statistical method of increasing resolu-
bei n g used for trigger arming, its wi dth tion wh ic h involves ma king α number
an d position are i ndicate d
b
y the inten- of measurements and averaging the re-
sified zone on the
d
is play. sults . When measuring
p erio d, for ex-
The 7D15
p
rovides th ree ty pes of gates.
am ple, with th e Χ1000 AVER G
p
us hbut-
T h e TRUE GAT E is the actual gate
ton
p
resse d, the cou nter meas u res the
waveform ge n erated eac h time t he
time for 1000 cycles an d divides the
co unter ta kes α measurement . It ty p i-
result by 1000 to obtain t h e time of one
cally
h as α low re p rate and is difficult
period . Figs. 3, 4, an d 5 s how grap h s of
to use,
b
ecause it is
d epen dent on t h e
resolution vs .
p eriod, resolution vs . time
settin g of th e DISPLAY TIME control.
interval, an d resolution vs . freq uency
The PSEU DO GATE is α
h ig h re petition
for the various settings of the CLOC K
re p lica of the TRUE GATE, an d is the
an d AVERG
p
us h butto n s . Note that for
most useful of these two. The PSEU DO
period meas u rements, resolution is in-
GATE has α
h
ig h er re p rate, because it
crease d 1000 times from the Χ1 to the
Χ1000 AVER G setting .
F
or time interval
meas urements, the maximum resolution
is increase d from 10 ns to 2 ns (for the
10 ns cloc k rate)-an increase in reso~
lution of 5 times .
The resolution you select also deter-
mines the maximum time interval you
can measure wit h out overflowing t h e 8
d igit C R T reado u t .
F
or exam p le, if α
resolution of 10 ns is selecte d (10 ns
cloc k rate a nd Χ 1 measurement aver-
aging), t h e lo n gest time interval t h at
can be measure d before overflow oc-
curs is .99999999 secon d . T h e selecte d
resolution
d
etermines the u nits of the
least sign ificant digit of the
d
is play . For
α longer time interval, you m u st select
less resolution . T his is
p
rovi ding that
you care about the most significant
d igit of the meas u reme nt. If you are
merely trying to resolve α small time dif-
fere n ce,
and do not care about th e
actual time interval, you ca n overflow
t h e co unter and still obtain t h e maxi-
mum resolution
d
esired.
Accuracy is
d
efined as the ratio (in
p
er-
cent) of the worst case error for α mea-
su rement to the actual measurement,
an d is α fun ctio n of resol ution and the
accuracy of the crystal co ntrolle d cloc k
oscillator . As Figs. 3, 4, an d 5 illustrate, *
Ι
accuracy te nds to i ncrease with in-
creases in the perio d, time interval, or
freq uency being measured . T h e 7D15
cloc k oscillator
h as an accuracy of 0.5
pp m, whic h
p
rovi des time measurement
accuracies of up to 0.0001% on long
time intervals-muc h greater than
t
he
1 % accuracy of an oscillosco p e.