Operating I nstructions-7844/R7844 Operators
2. Adjust the vertical and horizontal Position controls to
center the display on the graticule.
3. Release the B EA M FI N D E R switch; the display should
remain within the graticule.
Control I llumination
The CONT R O L I L LUMINATION switch sets the i l l um ina
tion level of the l ighted push button switches on the p l ug-in
units. The positions available are O F F , LOW and HIGH.
This switch is located on the rear panel of the 7844 and the
left side panel of the R7844. The CONT R O L I L LUMINA
TIO N switch does not affect the function indicator l ights
(such as TRIG'D lights or SIN G L E-SWEEP R EA DY lights) .
Calibrator Output
The internal calibrator provides a convenient signal for
checking basic vertical gain and sweep timing. The cali bra
tor signal is also very useful for adjusting probe compensa
tion as described in the probe instruction manual. I n addi
tion, the calibrator can be used as a convenient signal source
for application to external equipment. See Table 2- 1 in the
Specification section for cal i brator accuracy.
VOLTAGE.
The calibrator provides accurate output voltages
at the CALIB RATOR Output connector from 4 m i l l ivolts
to 4 volts in decade steps into loads of more than 1 00 kil
ohms. In addition, it provides from 0.4 m i l l ivolts to 0.4
volt into a 50 ohm load.
C U R R ENT.
The current loop provides a 40 m i l l iampere
output which can be used to check and calibrate current
measuring probe systems. The current output is selected by
the CALIBRATOR switch when set to the 40 mA position_
The current signal is obtained by clipping the probe around
the current loop. The arrow above the current loop ind icates
conventional current flow; i_e., from plus to m i n us. Forty
m i l l iamperes is available from the R7844 when the optional
current loop adapter is used (Tektronix part 0 1 2·0031-00)
and the CA LIBRATOR is set for a 4 volt output.
R EPETITION RATE.
The repetition rate of the cal ibrator
is 1 kilohertz. The calibrator circuit uses frequency-stable
components to maintain accurate frequency and constant
duty cycle. Thus, the cal i brator can be used for checking
the basic sweep timing of time-base units.
WAVE SHAPE.
The square wave output signal of the cal i
brator can be used as a reference wave shape when checking
1 - 1 4
or adjusting the compensation of passive, high-resistance
probes, The square wave has a flat top so any distortion i n
the displayed waveform is d u e t o improper probe compen
sation.
Probe Power
Two PROB E POWE R connectors on the rear panel of the
7844 and the front panel of the R7844 provide power for
accessories_ Current from these connectors is l i m ited, there
fore it is not recommended that they be used as a power
source for applications other than the compati ble probes or
other accessories which are specifical l y designed for use
with this system,
Horizontal Display Mode Combinations
The HORIZONTAL M O D E switch allows both beam 1 and
beam 2 to be controlled by either A H O RIZ or B HORIZ
compartments. When both beams use the same time-base
unit as a sweep source, the other unused horizontal compart
ment can be used for special purpose plug-in units such as a
counter, digital voltmeter, etc.
The H O RI Z SEP ( 1 ) control provides horizontal position
ing of beam 1 in addition to the Position control of the
horizontal plug-in unit selected by the BEAM 1 HORIZON
TA L MODE switch. When the same time base is selected
for horizontal deflection of both beams, the H O RIZ SEP ( 1 )
control can be used to align a n event on the beam 1 trace so
that the timing of both beams coincide,
Vertical Display Mode Combinations
The 7844/R7844 Option 2 1 model has dedicated vertical
plug-in compartments. The left vertical compartment is
directly connected to the beam 1 trace and the right vertical
compartment is directly connected to the beam 2 trace.
The 7844/R 7844 standard model has vertical crossover
switching. The V E RTICAL MODE switch allows both the
beam 1 and beam 2 traces to be controlled by either vertical
plug·in compartment. When both beams are being control led
by the same vertical compartment, the VERT SEP ( 1 ) con
trol becomes operational. The V E RT SEP ( 1 ) control wil l
position the beam 1 display above or below the beam 2
d·lSplay.
Beam
2
Display Characteristics
The readout display is produced on a time-shared basis with
the beam 2 crt display in both the PU LSE D and free-run
(non-pulsed) R EADOUT modes.
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