Tektronix 7844, Инструкция по эксплуатации

Страница: 18 / 50

Operating I nstructions-7844/R7844 Operators
2. Set the horizontal deflection factor to display 5 cycles of
the CALIBRATOR signal.
3. Adjust the FOCUS control so that the top and bottom
portions of the waveform are as thin as possible but not
elongated.
Trace Alignment
The TRACE ROTATION control allows the trace to be
aligned with the horizontal graticule lines.
Position both beams to the center horizontal line and adjust
the TRACE ROTATION adjustment so that the 2 traces are
parallel with the horizontal graticule lines.
Graticule
The crt graticule lines are internally marked on the face of
the crt. This feature eliminates measurement error due to
faceplate parallex. The crt faceplate is divided into 8 verti­
cal and 10 horizontal divisions. Each division is 1 centimeter
square, each major division is divided into
5 minor divisions.
The gains of the vertical and horizontal compartments are
calibrated to the crt graticule. Figure 1�3 illustrates the grati�
cule and defines the various measurement lines. The termi�
no!ogy defined here will be used in all discussions involving
graticule measurements.
NOTE
Two types of crt graticules have been used in some
Tektronix oscilloscopes. One graticule has
0% and
100% rise time reference points that are separated by
6 vertical graticule divisions. The other graticule has
the 0% and 100% rise time reference points separated
by 5 vertical divisions. In your manua/� illustrations
of the crt face or risetime measurement instructions
may not correspond with the graticule markings on
your oscilloscope.
Light Filters
The tinted filter provided with the standard instrument,
minimizes light reflections from the face of the crt to im­
prove contrast when viewing the display under high ambient
light conditions. This filter should be removed for waveform
photographs or when viewing high writing rate displays. To
remove the filter, pull outward on the bottom of the plas-
tic crt mask and remove it from the crt. Remove the tinted
filter (leave the metal light shield in place) and snap the
plastic crt mask back into place.
Do not remove the clear plastic implosion
shield.
An optional mesh filter is available at extra cost (included
with Option 3). This filter provides shielding against radiated
emi (electro-magnetic interference) from the face of the crt.
1-12
It also serves as a light filter to make the trace more visible
under high ambient light conditions. The mesh filter fits in
place of the plastic crt mask and the tinted filter. The filter
can be ordered by Tektronix Part 378-0603-00.
The apparent light output from the crt is reduced when
tinted and emi filters are used. Therefore, these filters
should be removed to obtain the best visible photographic
writing rate.
Graticule I llumination
The GRAT ILLUM control varies the illumination of the
graticule lines. The GRAT ILLUM can also be operated in
the PULSED mode. With the G RAT I LLUM control set to
the PULSED detent and the EXT/BEAM 2 GATED switch
set to the BEAM 2 GATED position, the graticule will be
illuminated momentarily after beam 2 completes a sweep.
With the EXT/BEAM 2 GATED switch set to the EXT posi·
tion, the graticule can be momentarily illuminated either by
depressing the GRAT I LLUM MANUAL push button or by
SECOND
CENTER
TENTH
VERTICAL VERTICAL VERTICAL
LINE
LINE LINE
t t
roo-, .
....
CENTER
HORIZONTAL +
LINE
r
,--
•
1675·7
Fig.
1-3.
Definition of measurement lines on the
7844/R7844
grati­
cule.
applying a remote signal to the GRAT/READOUT SINGLE
SHOT BNC connector, located on the rear panel (see Table
2-1 for signal requirements). When operating in the PULSED
mode, the level of illumination is controlled by the GRAT
I LLUM, PRESET screwdriver adjustment.
Readout Display
The Readout System displays alphanumeric plug-in unit
scale factors on the crt,in conjunction with the displayed
analog waveform. Each installed plug-in unit encodes the
readout information into a word. Up to 8 words of readout
information can be displayed on the crt (2 channels from
each of the 4 plug-in compartments). Figure 1�4 illustrates
readout word placement on the crt. Notice that the readout
REV. A, SEPT. 1975