Operating Instructions— Type M
VOLTS/CM (All channels)
.02
MODE (channel A)
DC NORM.
MODE (channels B, C and D)
OFF
VAR. GAIN (all channels)
CALIB.
POSITION (all channels)
Centered
ALTERNATE/CHOPPED
ALTERNATE
1. Position the trace to about + 2 cm with the channel A
POSITION control.
2. Set the channel B MODE switch to the DC NORM, posi
tion and position the B trace to about +1 cm with the
channel B POSITION control.
3. Set the channel C MODE switch to DC NORM, and posi
tion the C trace to about —1 cm with the channel C POSI
TION control.
4. Set the channel D MODE switch to DC NORM, and
position the D trace to about —2 cm with the channel D
POSITION control. This makes a total of four traces which
appear on the crt screen. For each sweep cycle one channel
is conducting and the others are cut off. The channels are
switched alternately at the end of each sweep cycle, during
retrace intervals.
5. To observe the alternate trace switching cycle at a
slower rate, decrease the sweep rate to 0.1 sec/cm.
6. To observe the CHOPPED mode of operation set the
ALTERNATE/CHOPPED switch to the CHOPPED position.
7. Set the oscilloscope triggering controls for +lnternal
triggered-sweep operation. Notice that all four traces seem
to start simultaneously and continue on across the screen.
8. Increase the sweep rate to 10
fi
sec/cm. Adjust the oscillo
scope Triggering Level control to obtain a stable display.
Notice that each trace is composed of several short-
duration elements with switching-transient traces existing
between the channels. [To blank out the switching tran
sients, set the CRT Cathode Selector switch (located at the
rear of most Tektronix oscilloscopes) to the Dual-Trace
Chopped Blanking position.]
All four channels are being switched successively at a
rate of approximately 1 me. Increase the sweep rate to 1
/Asec/cm. Observe that each channel conducts for about
1
fisec
and then is cut off for 3 ^isec while the three other
channels each conduct for 1
/xsec.
Chopping rate of each
channel is 250 kc (1 me divided by the number of channels
in use). Approximate switching time between channels is
0.1
fisec
(see Fig. 2-2a).
9. Now set channel B and D MODE switches to OFF.
Notice that the M Unit switches between channels A and C
only. Each channel conducts for about 1
fisec
and then is
cut off while the other channel conducts for an equal time
(see Fig. 2-2b). Chopping rate for each channel is now
approximately 500 kc.
GENERAL OPERATION
Any of the four amplifier channels can be used inde
pendently by rotating the appropriate MODE switch to
one of the DC or AC positions and connecting the signal
to be observed to the appropriate input. The following
remarks apply equally to each channel.
=
1 /Asec..
■*- = 3 /xsec.—
= 0.1 /xsec
H
(a)
= 1 fA sec.^
—►
-
I
I
I
:
( ♦ s O . l
/usee.
' \
1
’
(b)
Fig. 2 -2 . (a ) Chopping rate of each channel is approximately
25 0 kc, and
(b)
the chopping rate is about 5 0 0 kc.
Switching
rate is approximately 1 me.
Sweep rate of the oscilloscope is
1 /zse c/cm.
Signal Connections
The signal(s) to be displayed is applied to the appropri
ate input connector on the front panel of the M Unit. For
best results, following are some precautions you should
observe when making the connections.
1. It is often possible to make signal connections to the
M Unit with short-length, unshielded test leads. This is
particularly true for high-level, low-frequency signals. When
such test leads are used, you must also use a ground con
nection between the M Unit or oscilloscope chassis ground
and the chassis of the equipment under test. Position the
leads away from any stray electric or magnetic field source
to avoid erroneous displays.
2. In many low-frequency applications, however, unshielded
leads are unsatisfactory for making signal connections be
cause of unavoidable pickup resulting from magnetic fields.
Whenever possible, use shielded (coaxial) cables. Be sure
that the ground conductors of the cables are connected to
the chassis of both the oscilloscope and the signal source.
3. In broadband applications, it may be necessary to ter
minate the coaxial cable with a resistor or an attenuator
equal to the characteristic impedance of the cable, to pre
vent resonance effects and ringing. It becomes more neces
sary to terminate the cable properly as the length of the
cable is increased. The termination is generally placed at
the oscilloscope end of the cable, although many sources
require an additional termination at the source end of the
cable as well.
4. As nearly as possible, simulate actual operating condi
tions in the equipment under test. For example, the equip-
2-2
