Every selected input range allows a 200% overload without any change of input
resistance or auto ranging. This 200% overrange is designed to allow for
smaller voltage overloads without affecting the measurement. Within this
200% overload, the amplifier is also able to respond with normal rise/fall times
and the signal is restored within the standard selected range.
When exceeding the 200% overload, the input impedance might start to
increase. The impedance increase lowers the input current. A positive side
effect of the lowered current is that the dissipated heat is lowered. It is the
excessive heat dissipation that typically damages the input channel.
The first action
of the system is to add an additional current load to the input
signal to create an extra voltage drop in the input series resistance. The
resulting additional current depends on several factors and is therefore
unpredictable. A negative side effect of this additional current is that the extra
power is dissipated in the input section, which in turn results in additional heat
dissipation.
Secondly,
the input section starts switching to disconnect itself from the input
signal to reduce the power dissipated within the lower ranges of the amplifier
(≤
±
5 V ranges).
+12V
-12V
Out
+12V
+12V
-12V
Compare
x3
u1
x2
x1
-12V
> ±5V
+
1 / 100
990
k
Ω
1
0
k
Ω
≤ ±5V
+12V
+12V
-12V
Compare
-12V
> ±5V
-
1 / 100
9
90
k
Ω
1
0
k
Ω
≤ ±5V
f(x1...xn)
x3
u1
x2
x1
f(x1...xn)
Figure 12.22:
Input overload protection
-
Schematic diagram
GEN3t
I3995-3.1 en HBM: public
275