Tektronix 2445, Инструкция по эксплуатации

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Operating Inform ation—2445 Service
OPERATING CONSIDERATIONS
This part contains basic operating information and
techniques that should be considered before attempting to
make any measurements w ith your instrument.
GRATICULE
TIME AND VOLTAGE
MEASUREMENTS
The 2445 provides three basic ways to make time
measurements and tw o basic ways to make voltage measure­
ments. These methods require varying degrees o f time and
care and can result in varying degrees o f accuracy.
The graticule is internally marked on the faceplate of
the crt to eliminate parallax-viewing error and to enable
accurate measurements (see Figure 2-9). It is marked w ith
eight vertical and ten horizontal major divisions. In addition,
each major division is divided into five subdivisions. The
vertical deflection factors and horizontal tim ing are cali­
brated to the graticule so that accurate measurements
can be made directly from the crt. Also, percentage marks
fo r the measurement of rise and fall times are located on
the left side o f the graticule.
Figure 2-9. Graticule measurement markings.
Using graticule markings fo r determining voltage or time
values produces the least accurate measurement values.
This method should be used only fo r measuring very-low-
repetition-rate signals or for single-shot measurements
which require a photograph fo r viewing.
The A t and A V cursors provide fo r better accuracy and
easier operation than using the graticule, and they should
be used in most measurement situations. Use o f the cursors
avoids vertical- and horizontal-gain errors and crt-linearity
errors. Cursors also eliminate the inconvenience o f counting
and interpolating graticule markings.
The Delayed Sweep mode provides the highest accuracy
for making time measurements. This method avoids errors
introduced either by visual-resolution limits or by slight
mismatches between the sweep and the cursors.
More details relating to various measurement techniques
are contained in "Basic Applications," Section 6 of the
Operators Manual.
GROUNDING
The most reliable signal measurements are made when
the 2445 and the unit under test are connected by a com­
mon reference (ground lead) in addition to the signal
lead or probe. The probe's ground lead provides the best
grounding method fo r signal interconnection and ensures
the maximum amount of signal-lead shielding in the probe
cable. A separate ground lead can also be connected from
the unit under test to the oscilloscope ground receptacle on
the fro n t panel.
2-15