Tektronix 1A5 Instruction Manual page 24

Operating Instructions — Type 1A5
Fig. 2-12. Effect of external load connected to Comparison Volt ­
age (Vc) MONITOR jack. (Does not apply when VOLTS/CM con ­
trol is set to 5 V, 10 V or 20 V positions.)
Overdrive Recovery Time
In an/ oscilloscope, when a signal causes the trace to
deflect off the CRT face, a certain amount of recovery time
is required before the trace will return and waveform obser-
vation/measurement can continue.
Method Advantages
Simplicity.
1. Open test leads.
2. Unterminated Full sens i t i vity.
coaxial cable.
3. Terminated Full sens i tvity.
coaxial cable. Ter ­ Total
width.
mination at 1A5
flat-response resis ­
input.
tive loading. Long
cable with uniform
response.
Less reflection from
4. Same as 3, with
20 pF at termina ­
coaxial attenuator
tion.
at termination.
2-16
This is annoying and
TABLE 2-3
Passive Signal Coupling Methods
Limitations
Limited frequency
response. Subject
to stray pickup.
Limited frequency
response. High ca ­
pacitance of cable.
Presents R O (typi ­
cally 50 Ω) loading
1A5 band ­
at end of coaxial
Rela ti vely
cable. May need
blocking capacitor
to prevent DC
loading or dam ­
age to termination.
Sensitivity is
duced (increased
deflection factor).
time consuming. The operator can minimize this problem
by using the following procedure:
1. AC operation. Use the precharge/discharge procedure
outlined earlier in this section.
2. AC single ended operation.
nal, set the VOLTS/CM control to allow all of the maximum
expected AC waveform to appear on the CRT viewing area.
3. DC single ended operation.
nal, set the VOLTS/CM control to allow all of the maximum
expected AC + DC waveform to appear on the CRT view ­
ing area.
4. Differential Comparator operation.
signal Input AC-GND-DC switch at GND and the Vc POLAR ­
ITY switch at 0 until the signal and a comparable value of
Vc are inserted. Simultaneously switch the signal Input AC-
GND-DC switch to DC and Vc POLARITY switch to the
polarity of the signal being common-moded.
of the signal amplitude, only the difference between Vc
and the signal will appear as trace deflection.
5. Differential Amplifier Operation. Place both AC-GND-
DC switches at GND before connecting signal sources to
the Type 1A5. After connections have been made, simultane ­
ously switch both AC-GND-DC switches to either AC or DC
as desired. Regardless of the amplitude of the signals, only
the difference between the two will cause trace deflection.
6. Active Differential Probe operation. Keep Vc POLARITY
at 0 and Differential Probe lamp off until both contacts
of the active Differential Probe are connected. Then press
PUSH ON/OFF button to accept active probe signals.
Accessories
Source Loading
Required
BNC to Binding 1 Mf2
Post adapter (103 ­ at input, plus test
0033-00). Two test leads.
leads.
Coaxial cable with 1 MΩ
BNC connector(s). plus cable capaci ­
tance.
R O plus 20 pF at
Coaxial cable with
BNC connectons) 1 A5 end of coaxial
R O termination at cable
1A5 input. (BNC reflections.
50 ft Termination
011 -0049-00).
R O only.
re ­ BNC coaxial atten ­
uators.
Before inserting the sig ­
Before inserting the sig ­
Keep the selected
Regardless
Precautions
S tra y pickup.
and 20 pF
s er t a 47-ohm re ­
s i s t or in series with
the leads.
High capacitive
and 20 pF
loading.
Reflection from 20
pF at input.
and AC load on
can cause
test point. Power
limit of termina ­
tion.
DC and AC load ­
ing on test point.
Power limit of at ­
tenuator.
In ­
DC