Functional Safety Manual
for the Memosens transmitter Liquiline M CM42 SIL
Version: Page:
2.0
20 of 72
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Voltage supervision:
(The following statements can be used for a FMEDA of the complete safety function
including the PLC, etc.)
o If you are using the LO error current, you must use a voltage
supervision on both outputs and drive the system to a safe state, if
the voltage drops below 15,5V.
o If you are using the HI error current, you must use voltage
supervision on current output 2 and drive the system to a safe state,
if the voltage drops below 9V. The current output 1 is supervised by
the Liquiline M CM42 system and is reset if the voltage on output 1
drops below 9V.
o We recommend using two independent voltage supplies for
the two current loops. Then all errors lead to a safe state, except if
the voltage supply on current output 2 has an error and there is an
error current on current output 2 or a measurement signal (4-20
mA) on both outputs. For these two cases, the voter detects the
error with a DC of 90%.
o If you are using just one voltage supply for both current outputs, the
following applies:
If the voltage supply has an error, the voter detects all voltage errors
with a DC of 60%.
The following table gives an overview of the device status in SIL mode:
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