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Operating Instructions— Type M
menf should work into a load impedance equal to that
which it will see in actual use.
5. Consider the effect of loading upon the equipment under
test due to the input circuit of the M Unit. The input circuit
can be represented by a resistance of 1 megohm (± 1 % )
shunted by a capacitance of approximately 47 picofarads.
With a few feet of shielded cable, the capacitance may
well be 100 picofarads. Where the effects of these re
sistive and capacitive loads are not negligible, you might
want to use a probe in the manner described next.
Use of Probes
An attenuator probe having a standard length cable
(42" long) lessens both capacitive and resistive loading,
but at the same time reduces sensitivity. The attenuation
introduced by the probe permits measurements of signal
voltages in excess of those that can be accommodated by
the M Unit alone. When making amplitude measurements
with an attenuator probe, be sure to multiply the observed
amplitude by the attenuation of the probe (marked on the
probe).
An adjustable probe capacitor compensates for variations
in input capacitance from one plug-in unit to another. To
assure the accuracy of pulse and transient measurements,
this adjustment should be checked frequently.
To make this adjustment, set the oscilloscope calibrator
controls for a calibrator output signal of suitable ampli
tude. Place the MODE switch for the channel in use to
DC NORM. Touch the probe tip to the calibrator-output
connector and adjust the oscilloscope controls to display
several cycles of the waveform. Adjust the probe variable
capacitor for best square-wave response, as shown in the
right-hand picture of Fig. 2-3.
Deflection Factor
The amount of vertical deflection produced by a signal
is determined by the signal amplitude, the attenuation factor
(if any) of the probe, the setting of the VOLTS/CM switch,
and the setting of the VAR. GAIN control. Calibrated
deflection factors indicated by the settings of the VOLTS/CM
switch apply only when the VAR. GAIN control is set to
the CALIB. position. Serious errors in display measurements
may result if the setting of this control is unintentionally
moved away from this position.
The range of the VAR. GAIN control is approximately
2.5 to 1 to provide continuously variable (uncalibrated)
vertical-deflection factors between calibrated settings of the
VOLTS/CM switch. The VAR. GAIN control can be manu
ally rotated continuously in either the clockwise or counter
clockwise direction, thus permitting the control to be set
quickly to any desired position. The control has one detent
position (CALIB.), which is the calibrated deflection factor
setting.
Voltage measurements may be made directly from the
oscilloscope screen by noting the calibrated VOLTS/CM
switch setting for the applicable channel and the amount
of vertical deflection on the crt. Multiply the deflection on
the screen by the setting of the VOLTS/CM switch and the
attenuation factor, if any, of the probe.
MODE Switch
The MODE switch has five positions: DC NORM., AC
NORM., OFF, DC INV. and AC INV. To display both the
ac and dc components of an applied signal, set the MODE
switch to one of the DC positions; to display only the ac
component of a signal, set the MODE switch to one of the
AC positions.
In the AC positions of the MODE switch, the dc com
ponent of the signal is blocked by a capacitor in the input
circuit. The lower frequency limit (3-db point) of the M
Unit is about 2 cps (0.2 cps if using a 10X attenuator probe).
Therefore, some low-frequency distortion of signals with
components below this frequency will result if the AC posi
tions are used.
It may be desirable, at times, to invert the displayed
waveform, particularly when using the multi-trace feature
of the M Unit. With the MODE switch you can choose
either a normal or inverted display, and either dc or ac
coupling. In the DC- or AC-NORM. positions the displayed
waveform has the same polarity as the input signal. In
the DC- or AC-INV. positions the displayed waveform is
inverted.
Placing the MODE switch to the OFF position turns the
channel “ off” , disconnects the input signal, and excludes
the channel from the electronic switching cycle.
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2-3
Fig. 2 -3 . Probe compensation waveforms.
Содержание M 531
Страница 43: ...RIGHT SIDE Parts List Type M http manoman sqhill com...
Страница 45: ...Parts List Type M LEFT SIDE 0 0 0 IP 6 6 http manoman sqhill com...
Страница 56: ..._____________ CHANNEL A __________ SIGNAL OUTPUT AMPLIFIER 1 t y p e m p l u g i n u n i t AI...
Страница 64: ...TYPE M TENT SN 9660 CHANGE TO Q5344A B ELECTRICAL PARTS LIST CORRECTION 151 0232 00 Silicon Dual M15 594 170...