HBM Genesis series Technical Note page 18

GN610, GN611 Isolation and type testing
Figure 6.1: Input Overload protection - Schematic diagram
Thermal monitor of the input channels
Any overload condition has the same end result: extra heat generated within
the channel. Not only because of the extra current through the input resistance,
but also because internal amplifier sections will be driving their local output to
maximum levels creating excessive heating within the amplifier.
As a third protective mechanism every input is equipped with a thermal sensor
to monitor the local temperature. When the local temperature reaches
maximum levels the system will automatically start changing the user selected
input range to reduce the dissipated heat. As the heat dissipation will not
immediately start the auto ranging, short overloads will not results in auto
ranging. Longer overload conditions will lead to higher local temperature and
this will start the auto ranging process.
Whenever an overload condition pushes local temperature to above the
maximum level, the input range will be adapted to a factor 10 less sensitive
range. E.g. User selected ± 40 mV range, when required the system will change
the range to ± 400 mV. As this might not be enough due to an even higher
overvoltage, the system keeps on monitoring the local temperature. If the local
temperature doesn't reduce within the expected response time, the system will
automatically increase the input range with a factor of 10 for a second, third or
how many times required to reach a safe condition not to increase local
temperature anymore.
18 HBM public