Tektronix 323, Инструкция по эксплуатации

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Operating Instructions— Type 3 2 3
1/1 Oth of the source voltage available to the oscilloscope
vertical input connector.
The peak-to-peak measurement which can be made with
the P6049 Probe-Type 323 Oscilloscope combination is
500 V DC + peak AC. Other Tektronix probes which allow
measurement of voltages as high as 40 kV are available for
use with the Type 323 Oscilloscope.
CAUTION
Never apply voltages in excess of 500 V to the VERT
INPUT connector or to the P6049 Probe. Use a
high-voltage probe to reduce higher voltages to
an acceptable level.
Signal Source Resistance and Oscilloscope Input
Resistance
The oscilloscope input resistance (1 MO) and the signal
source resistance form a voltage divider. When the input
resistance is high with respect to the source resistance, dis­
play amplitude for DC and low-frequency AC signals is a
relatively accurate evaluation of the signal at the source.
See Fig. 2-9(A).
As the size of the oscilloscope input resistance compared
to the signal source resistance decreases, the display ampli­
tude decreases. See Fig. 2-9(B). In addition to providing
an incorrect display, such a situation loads a circuit to the
point where an evaluation is being made of a false circuit
performance.
The source-to-oscilloscope resistance ratio must therefore
be kept high. The 1 MO oscilloscope resistance is sufficient
for most applications. However, when the signal source im­
pedance is as high as 0.11 MO, approximately 10% error is
introduced. This error can be computed in DC and low-
frequency applications, and the display evaluation can be
corrected accordingly.
An easier method is to use a X 10 probe and a 10 times
more sensitive volts/div setting. The P6049 Probe and Type
323 Oscilloscope combination have a resistance of approx­
imately 10 MO. When used to evaluate the above-mentioned
0.11 MCI circuit, the ratio of oscilloscope resistance to sig­
nal source resistance is increased to approximately 91:1 and
display amplitude error is reduced to approximately 1%.
Another important consideration is that the loading effect on
the circuit becomes negligible and circuit performance is
not affected.
Signal Frequency Versus Signal Source
Capacitance and Oscilloscope Input
Capacitance
The 47 pF oscilloscope input capacitance is of little con­
cern when measuring DC or low-frequency signals. How­
ever, as frequency increases, the oscilloscope input capac­
itance in parallel with the signal source lowers the effective
load impedance. Parallel capacitance inserted by signal
transporting leads adds to the oscilloscope input capacitance
and further lowers effective load impedance, decreasing AC
and transient waveform display amplitudes. Signal trans­
porting lead capacitance must therefore be kept as low as
possible for AC or transient measurements.
When the signal source capacitance is high with respect
to the oscilloscope input capacitance, AC display amplitudes
are relatively accurate. The signal source capacitance to
oscilloscope capacitance ratio can be improved by insertion
of an attenuator probe in the signal path. Its effect upon
AC and transients will be essentially the same as was its
effect upon DC, both in increasing the effective range of
the oscilloscope and in reducing loading effects.
Circuit current can be monitored with the Type 323 Oscil­
loscope and a current probe. One type of probe uses a
device which can be clamped around or removed from the
current-carrying wire in a few seconds. It is especially use­
ful in working with current-driven transistor circuitry.
A summary of signal transporting information is provided
in Table 2-1. Additional information concerning all Tektronix
probes is contained in the Tektronix catalog.
PROBE ADJUSTMENT
Variations of total input capacitance and resistance occur
with different combinations of oscilloscopes and probes.
Therefore, many attenuator probes are equipped with ad­
justments to insure optimum performance. Explanations for
performing Tektronix Probe adjustments are contained in
the applicable probe manuals.
Because the P6049 Probe is a standard accessory for the
Type 323 Oscilloscope, that particular adjustment procedure
is repeated here.
P6049 Probe Adjustment Procedure
(a) Preset the Type 323 Oscilloscope controls as fol­
lows:
2-14
Fig. 2-9. Source resistance versus oscilloscope in p u t resistance.