Analog modules
9.2 SM 336; AI 6 x 13 Bit
Fail-safe signal modules
188
Installation and Operating Manual, 01/2010, A5E00085586-10
WARNING
The stability of the external sensor supply must conform to the desired safety requirement
class SIL 2, 3. To ensure that the sensor functions problem-free, we recommend one of the
following options:
Use of a redundant external sensor supply
or
Monitoring of the external sensor supply for undervoltage/overvoltage, including
shutdown of the sensor supply when a fault is detected (single-channel for SIL 2; two-
channel for SIL 3)
Recommendation: Internal sensor supply
You are strongly advised to use the short circuit-proof internal sensor supply of the module.
This internal sensor supply is monitored and its status is indicated at the Vs LED (see Figure
Front view of SM 336; AI 6 x 13 Bit).
Isolated transducers
The isolated transducers are not bonded to local earth potential. These transducers can be
operated with floating potential. Local conditions or interference may cause potential
differences U
CM
(static or dynamic) between the measuring lines M- of the input channels
and the reference point of the measuring circuit M
ANA
.
It is advisable to wire M- to M
ANA
to prevent common mode voltages in excess of the
permitted value for U
CM
when operating the equipment in areas subject to heavy EMC
interference.
Non-isolated transducers
The non-insolated transducers are bonded to local earth potential. Always interconnect M
ANA
with earth potential. Local conditions or interference may cause potential differences U
CM
(static or dynamic) between the locally distributed measuring points.
If common mode voltage exceeds the permissible value for U
CM
, you must provide for
equipotential bonding conductors between the measuring points.
