Tektronix 7a11 Instruction Manual page 105

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EK
T
R
O
N
IX®
cοm
m
lttι
d
to
tιc
hn
k
ιl
ικeΝ lιηα
C
HANGE:
M
A
N
UA
L
C
H
A
N
G
E
I
NF
O
RM
ATIO
N
PROD UCT
7Α 11
D
ESC R I P TION
ι
C
H A N G E REFEREN C E
C
l/874
DAT E
8-8-74
NOTE
D
amage to the input FET (field-effect transistor) Q23 in the 7Α 11 probe
i s possible under certain
s
ignal conditions
n
ot specified in
t
he
I
nstruction
Manual .
These conditions are as follows :
1 . The signal must be
n
egative and in excess of 100
V olts in magnitude
and
2 . The signal must be fast rise (less than .2
m
icroseconds) and,
3 . Sensitivity of t he 7Α 11 must be set at 5 mV, 10 mV, 20 mV, or 50 mV/div .
These conditions can occur by touching the probe tip to α
n
egative power
The act of switching the 7Α 11 sensitivity from 0 .1
V
/div to 50 mV/diν
to the FET α fast rise pulse almost equal in a mplitude to whatever
is applied at the probe tip . Thus, even if α
s
lowly
c
hanging
D
C
in
e
xcess of 100
V olts
h
as b een a pplied to the probe tip, damage to
may occur upon changing the 7Α 11 sensitivity from 0 .1 V
/div to 50 mV/
supply .
applies
v
oltage
v
oltage
the FET
div . Therefore
i
t
i
s
r
ecommended that the 7Α 11 sensitivity be
l
eft between
0 .1
V /div a nd 20
V
/div
w
hen voltages
m
ore
n
egative than -100
V
olts are
n
earby .
W hen using the AC Coupling Capacitor (011-0110-00)
i
t
i
s
r
ecommended that
the 7 Α 11 sensitivity be
l eft between 0 .1
V
/div
a
nd 20
V
/div until actual con-
nection to any high voltage circuit
h as been accomplished .
This allows the
A C Coupling Ca pacitor to charge up while the FET is protected by
o
ne or more
input attenuators .