Tektronix 585 - Page 13

Operating Instructions — Type 585
impedance. This can be done by connecting the proper
termination resistor at the input to the probe. Special adapt 
ers are available which permit direct connections of the
probe to Type N, BNC, UHF, and GR TYPE 874 connectors.
See the Accessories section of this manual for part numbers
and ordering information.
Compensating Attenuator Heads
To prevent waveform distortion, attenuator heads must
be compensated for high frequency losses. The compensation
should be checked each time an attenuator head is used.
The adjustment is made by displaying a square wave with
a risetime of 03 microsecond or faster on the oscilloscope
and adjusting the compensation control to eliminate any
distortion occurring in the leading edge of the waveform.
The 50-1 attenuator head can be successfully compensated
using the oscilloscope calibrator with its 1.0 microsecond
risetime. The adjustment should be made with the probe
input selector in the DC position. The compensation control
is a small plastic screw located in the body of the attenu 
ator head near the tip end.
Attenuator compensation is sensitive to pressures applied
laterally at the tip. Be sure to apply the probe and attenu 
ator combination to any test point directly without side
pressure.
Input Selection
The Input Selector switch on
input waveforms to be applied
scope (d c coupled) or to be
the Type P80 Probe permits
either directly to the oscillo-
applied to the oscilloscope
Fig. 2-5. Oscilloscope in triggered sweep operation, waveform
ladder diagram showing sequence of operations from input signal,
triggering signal, the sweep, and the ert display.
through a .01  f 150 volt capacitor (ac coupled). The input
Selector switch should be placed in the DC position when
low frequency waveforms are observed, to prevent distortion
and attenuation. The AC position should be used to elimi 
nate large d c components from waveforms applied to the
probe. The AC position blocks the d c component of a wave 
form and permits the variable component of the waveform
to be applied to the oscilloscope.
HORIZONTAL DEFLECTION SYSTEM
The Type 585 Oscilloscope features two independent time
base units: Time Base A and Time Base B. Either of the
two time bases may be displayed on the c rt at any time.
Controls affecting Time Base A and Time Base B operation
are in the correspondingly labeled blocks on the front panel.
The HORIZONTAL DISPLAY switch determines which time
base is used and the type of display to be presented. Time
Base A is selected when the HORIZONTAL DISPLAY switch
is in position A; Time Base B is selected when the switch
is in position B.
Sweep Rates
Time Base A has 24 accurately calibrated sweep rates
ranging from 0.05 microsceond to 2 seconds per centimeter.
Calibrated sweep rates are obtained only when the VARI 
ABLE TIME/CM control is snapped in the fully clockwise
position. The VARIABLE TIME/CM control permits the sweep
rate to be varied continuously between 0.05 microsecond
and approximately 5 seconds per centimeter. All sweep
rates obtained with the VARIABLE TIME/CM controls in any
position but fully clockwise are uncalibrated. Uncalibrated
sweep rates are indicated when the UNCALIBRATED lamp
is lit.
Time Base B has sweep rates ranging from 2 microseconds
to 1 second per centimeter in 18 steps. There is no VARIABLE
TIME/CM control for Time Base B. The red LENGTH control
adjusts the sweep length between approximately 10 and 4
centimeters.
Triggered Operation
For most uses of the oscilloscope a stable display of some
waveform is required. To accomplish this the oscilloscope
can be operated so that the horizontal sweep starts at a
given point on the displayed waveform. This is known as
“ triggered ” operation. For the present, we will refer to the
starting of the sweep, at the left side of the graticule, as
"triggering" the sweep.
Triggered operation is useful for observing a waveform
which may occur only once, or which may occur at random
intervals. For any of these uses, the oscilloscope can be
used in such a way that each horizontal sweep is triggered
by some waveform other than the one being observed, but
which bears a time relationship to the observed waveform.
The waveform used to start the horizontal sweep is called
the “ triggering signal", whether it is the waveform being
observed, or some other waveform. The instructions that
follow tell you how to select this signal. They also contain
information on triggering according to various modes, de 
pending on the nature of the triggering signal.
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