Tektronix 455, Instruction Manual, Page: 29 / 246

Operating lnstructions-455/A2/B2
20
AC-GIMD-DC-Selects the method for
coupling the
input signal to the vertical input amplifier.
signals at sweep rates slower than 0.5 m s/di
sweep rates o f 0.5 m s/div o r faster, the chof.
ments become visible. Use the alternate moc
faster sweep rates.
AC: Signals are coupled capacitively. Any dc
signal component is blocked. Low frequencies
are
attenuated (3 db down-0.707 X input
amplitude
at about 10 Hz directly or
1 Hz using a 10X probe).
Ac coupling causes tilting of square wave below
about 1 kHz.
GND: Disconnects the input of the vertical ampli­
fier from the input signal and connects it to ground
to provide a ground reference display. Connects
the input signal to ground through the input coup­
ling capacitor and a 1 Mf2 resistor to allow the
input coupling capacitor to be precharged by the
input signal.
DC: All components of the input signal are passed
to the vertical amplifier.
Do not use normal triggering because the display triggers o
the chopping transients. To obtain the best triggering re­
sults, set trigger source to channel 1 and trigger coupling to
high-frequency reject. If the input signals are not time
related, the channel 2 display will be unstable, and alternate
(A LT) mode should be used.
ADD: Displays the algebraic sum o f the signals
applied to the CH 1 and CH 2 input connectors.
V E R T M O D E—Selects the vertical amplifier operating
mode.
NOTE
When using the A d d m ode, keep both vertical
position controls as near m idrange as possible. i
CH 1: Displays only signals applied to the CH 1
input connector.
CH 2 (or X -Y ): Displays only signal applied to the
CH 2 input connector. This button must be de­
pressed for X-Y operation.
A L T (Alternate): The display switches between
the signals applied to the CH 1 and the CH 2 input
connectors. This switching occurs at the end o f
each sweep during retrace. This mode is u seful f o r
viewing both input signals at sweep rates of 0.5 ms/
div or faster. A t sweep rates slower than 0.5 ms/
div, the display flickers. Use the CHOP mode at
slower sweep rates.
T o o b ta in the best trigg ering results f o r non tim e-re late d
signals, set trigg er c o up lin g to low -freq ue ncy reject, trigger
source to norm al, and c a re fu lly adjust the trig g e r level. F or
tim e-related signals, set trigger coupling to low -freq ue ncy
reject and trigger source to channel 1.
01
The channel 2 IN V E R T switch allows display o f channel 1
plus channel 2 (IN V E R T button-out) or channel 1 minus
channel 2 (IN V E R T button-in). The channel 1 minus
channel 2 mode is useful for common mode rejection or dc
offset measurements.
I
© U N C A L Lamps— L ig h t u p to in d ic a te u n c a lib ra te d
d e fle c tio n fa c to rs w hen th e V A R c o n tro ls are m ove d
o u t o f th e ir d e te n t p o s itio n s .
I
© T R IG V IE W —This sw itch, w hen pressed, causes a
sample o f the signal present in the A Trigger A m p lifie r
to be displayed on the c rt. P a rtic u la rly useful fo r
view ing external triggers.
f
CHOP: The display switches between the signals
applied to the CH 1 and the CH 2 in p u t connectors. ___
This sw itching occurs at a fixe d rate o f about 250 [ 2 4 / IN V E R T -T h is sw itch, when set to the in position,
kHz. This mode is useful fo r viewing b oth in p u t inverts the channel 2 display.
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