19
NORM:Th e NORM switc h provid es no rma l trig gered sw eep o pera tion.The swee p re main s at r est u ntil the s elect ed trigge r sou rce
sign al cr osses the thres hold leve l set by the TRIG L EVEL contro l.Th e trig ger caus es one sweep to be generate d,after which
swee p ag ain r ema ins a t rest unti l trig gere d.In the N ORM po sitio n,the re will b e no trace unle ss an ade quate trig ger signa l is
present.I n the ALT mo de of dual trac e op erati on with NORM sweep s elec ted,t here will be tr ace u nless bot h ch annel 1 an d 2
sign als a re ad equa te fo r trig gering.
TV-V:Setting th e MO DE swit ch to the TV-V pos ition permits selec tion of ve rtical sy nc pu lses for sweep trig geri ng w hen
viewing c omp osite vid eo w aveforms .Ver tical sync pulses a re selecte d as trigg er to permit vi ewing of vert ical field s
and fram es of vide o.A swee p tim e of 2 ms /DIV is a ppro priate for view ing field s of vide o and 5ms /DIV for complete
fram es(tw o interlaced field s)of vide o.
T V H:Setting the MODE swi tch t o the TV-H po sitio n pe rmits sele ctio n of horiz onta l syn c pulses for s weep trig gerin g wh en
viewing comp osite vid eo waveforms . Ho rizon tal sync puls es ar e selected as t rigge r to perm it vi ewin g of horiz onta l fie lds o f
vide o.A swee p tim e o f abo ut 1 0us/DIV is ap prop riat e for disp layi ng lines of video.The SWP VAR co ntro l can be set to
disp lay th e ex act n umb er of wav eforms d esire d.
This oscillosc ope sync hronizes with only (-)p olari ty,th at is,the sync pulse s are neg ative and the video is p ositi ve as sho wn in
Figu re 4- 6.
(2 )Fun ctio ns of SOU RCE switch:
T he d ispla yed signal its elf o r a trigger sig nal w hich has a tim e
r elati onsh ip wi th th e displayed si gnal is re quire d to be a pplie d to the
trigg er cir cuit to displa y a st ation ary signa l on the CRT scree n.
T he S OURCE switc h is used for selec ting such a triggering s ourc e
CHl/ CH2 : The inte rnal trigg er method wh ich is use d mo st co mmonly. The sign al ap plie d to t he v ertic al inp ut te rmin al is
bran ched off f rom the p reamplif ier a nd is fed to the trig ger circu it thr ough the VERT MODE switch. S ince the triggering
signa l is the m easu red signal itse lf, a stab le wa vefo rm c an b e rea dily displayed on t he CRT s cree n. W hen in the DUAL o r
ADD operation, th e sig nal s elected b y the SOURCE switch is us ed as the trigg ering sou rce s igna 1.
-
.
Figure 4-6
20
Line: T he AC po wer line frequ enc y sig nal i s used as the t rigg ering signal. This meth od i s eff ectiv e wh en the m easu red
sig nal has a relation ship with the AC line frequ ency,esp ecia lly for me asur eme nts o f low lev el AC no ise o f au dio
eq uipment, thyr istor circ uits, etc.
EXT: T he sweep is tr igge red with an e xtern al s ignal app lied to the ex ternal trigger input ter minal. An external sig nal
wh ich has a peri odic rela tions hip with resp ect to the mea sure d sig nal is use d.Since the m easu red s igna l is n ot u sed
as the trigge ring sign al,th e wa vefo rms can b e di splay ed more independ ent t han the measu red s igna l.
(3)Fu nctions o f TRIG L EVE L co ntro l and SL O PE switch:
A swe ep trigger is d eveloped whe n the trig ger source sig nal cross es a prese t threshold le vel.Rotation o f the TRI G LE VEL
con trol v aries the thre shol d lev el.In the "+"d irection,the trigger ing threshold shif ts to a mo re po sitiv e va lue,a nd in the "-"
dire ctio n,the trig gerin g thr esho ld sh ifts to a more neg ative valu e.W hen the c ontrol is c ente red, the thresh old level is se t at
the appr oxim ate a vera ge o f the sign al used as the trigg ering source.
T he T RIG LEV EL c ontr ol adjusts the start of th e sweep t o almost any desired po int o n a wave form .On sine wav e sig nals,
the pha se at whic h sweep begin s is varia ble.Note that if th e TRIG L EVE L control is ro tated toward i ts ex treme+o r-setting,
no swee p will be developed in the NORM trigger mod e bec ause the trigg ering thr esho ld ex ceed s the peak amplitu de of the
sync sig nal.
When the TRIG SL OPE switch is set to the (+)posit ion(up), the s weep is d evelo ped from the trigg er so urce wav eform as it
cro sses the thres hold leve l in a pos itive -goin g direction.W hen the T RIG SLOPE cont rol is set t o the(-)p ositi on (d own ),a
sweep t rigg er is deve lope d fro m th e trig ger sourc e wavefo rm a s it c rosses th e thresho ld level in a ne gati ve-g oing direc tion .
Th is switch sele cts th e slo pe (polar ity) trigg erin g sig nal a s shown i n Fig ure4 -7.
TRIG LE VEL LOCK
Adjust leve l(28 )to fu lly c lock wise ,the trigg erin g level is lock ed a t a fi xed
v alue ,and stab le triggering is ma de witho ut requiri ng level a djus tmen t.
Th is Trigge r lev el lo ck fu nctio n is effec tive whe n the sign al amplitude
o n th e scr een o r the inpu t vo ltage of th e ex terna l triggeri ng s ignal is with in
the fo llowing r ange :
620 B/5 620NF/620BF/620 R:
640 B/65 0B/6 40BF/65 0BF /640 R/65 0R:
50Hz -- 2MHz:
1.0DIV
50Hz-- 20MHz:
1.5DIV
2M Hz -- 20MHz : 2DIV
20MHz-- 50M Hz :
3D IV
≥
≥
≥
≥
Slope
"-"Range
Figure 4-7
Level
+
-
Slope
"+"Range
