Tektronix 516 series Instruction Manual Download Page 15

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O perating Instructions — Type 5 1 6

Selecting the Trigger Source

CAL. OUT

D isplay several cycles of C a lib ra to r w aveform on crt screen.

Hold probe barrel and loosen locking sleeve.

Hold probe

base and adjust probe barrel fo r fla t-to p p e d square waves.

Hold probe barrel and carefully tigh ten locking sleeve.

Fig. 3-2. Probe compensation adjustment.

An adjustable capacitor in the probe body compensates

for  variations  in  the  input  capacitance  from  one  instrument
to  another  or  between  two  input  connectors  of  one  instru
ment.  To  insure  the  accuracy  of  pulse  and  transient  measure
ments,  this  adjustment  should  be  checked  frequently.  Fig.
3-2  illustrates  the  method  of  adjusting  the  compensation  of
the  probe.

TRIGGERED OPERATION

For most uses of your oscilloscope, you will need to get a

stable  display  of  some  recurrent  waveform.  In  order  to  ob
tain  a  stable  display,  it  is  necessary  to  start  the  horizontal
sweep  consistently  at  the  same  time  relative  to  recurring  cy
cles  of  the  input  waveform.  The  sweep  therefore  must  be
triggered  by  the  input  waveform  itself  or  by  some  waveform
which  bears  a  fixed  time  relationship  to  the  input  waveform.

The following instructions tell you how to select and use the
proper triggering signal for various applications of the oscil
loscope.

For most applications the sweep can be triggered by the

input waveform. The only requirement is that the input

signal be large enough to provide at least one-fifth of a

major graticule division of deflection on the screen at the

sensitivity  level  for  which  the  VOLTS/DIV.  control  is  set.  To
obtain  triggering  of  the  sweep  from  the  input  waveform,  set
the  black  TRIGGER  SELECTOR  control  to  either  the  +  INT.
or  the  —INT.  position  (the  significance  of  the  +   and  —  will
be  explained  in  a  later  paragraph).

For dual-trace operation, it is usually advantageous to

trigger  the  sweep  with  some  external  trigger.  In  this  way,
the  true  phase  relationship  of  the  two  waveforms  can  be
shown  and  triggering  is  obtained  more  easily.  In  order  to
obtain  a  stable  display,  it  is  necessary  that  the  external  trig
gering  waveform  bear  a  fixed  time  relationship  to  the  input
waveforms.  The  external  triggering  signal  must  be  at  least

0.2 volt in amplitude to assure proper triggering. To use an

external  waveform  for  triggering  the  horizontal  sweep,  con
nect  the  signal  to  the  TRIGGER  INPUT  connector  and  set  the
black  TRIGGER  SELECTOR  control  to  the  +EXT.  or  —EXT.
position.  External  triggering  may  also  be  used  with  single
trace  operation  where  desired.

When you are observing a waveform which bears a fixed

time  relationship  to  the  ac  line  frequency,  you  may  wish  to
trigger  the  sweep  from  the  line-frequency  waveform.  To  do
this,  place  the  black  TRIGGER  SELECTOR  control  in  the

+LINE or —LINE position.

When the black TRIGGER SELECTOR control is set to one

of the

positions (+INT., +EXT., -+ LINE), the sweep is trig

gered  on  a  positive  slope  of  the  triggering  signal.  When  the
control  is  set  to  one  of  the  —  positions  (—INT.,  —EXT.,
—LINE),  the  sweep  is  triggered  on  a  negative  slope  of  the
triggering  signal.  In  most  cases,  selection  of  the  triggering
slope  is  not  critical.

Selecting the Triggering Mode (HF SYNC,
AUTO., AC, DC)

The most useful triggering mode is the automatic mode,

obtained by setting the red TRIGGER SELECTOR control
to the AUTO, position. The automatic mode of triggering

provides a stable display with virtually any triggering signal

from  about  50 Flz  to  2 MFlz  in  frequency.  No  adjustment
of  the  STABILITY  or TRIGGERING  LEVEL  controls  is  necessary
since  these  two  functions  are  automatically  set  to  their  op
timum  values  internally.  (In  the  other  triggering  modes,  it

is necessary to set one or both of these controls to obtain

a  stable  presentation.)  In  addition,  the  automatic  mode  of
triggering  provides  a  free-running  trace  on  the  screen  in
the  absence  of  any  triggering  signal.  This  trace  may  be
used,  under  certain  conditions,  as  a  base  line  from  which  to
make  dc  measurements.  It  also  gives  a  constant  indication

of the readiness of the oscilloscope to accept a triggering
signal for the display of a stable waveform.

In the ac triggering mode, obtained by setting the red

TRIGGER SELECTOR control in the AC position, suitable
triggering can be obtained with signals from about 16 Flz

to 5 MFfz. When the ac triggering mode is used, it is usually

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