Endress+Hauser Liquiline M CM42, Руководство по функциональной безопасности

Страница: 15 / 72

Functional Safety Manual
for the Memosens transmitter Liquiline M CM42 SIL
Version: Page:
2.0 15 of 72
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This table includes all uncertainties (including EMI) except the precision of the slope,
zero point and temperature offset.
2.1.4 Safe calibration and adjustment (SAF3 and SAF4)
The safe calibration executes a safe calibration sequence, safe value computations and
safe interactions with the user for the calibration results using the display of the device.
The errors of all computations in the transmitter used for the slope and zero point of the
sensor are negligible, because they are well below the resolution used to store the
values in the sensor (slope
±
0.001pH/mV and zero point
±
0.001pH). This also refers to
the pH values needed for the used pH buffers at the given temperature.
The safe adjustment does store the results of the calibration in a safe manner into the
sensor interacting in a safe way with the user.
The safely calibrated and adjusted values in the sensor can then be used for the SIL
measurement of the pH value using SAF1 and/or SAF2.
Both safety functions can only be used in SIL mode and started in SIL measurement
mode. Both safety functions need the user to do some checks. To that end special
screens are used to communicate with the user in a safe way.
2.2 Safety-related signal and safe state
The safety-related signal is the analogue output (4..20 mA) on both current outputs.
There are no other safe outputs of the device.
The safe state is defined as either:
No current output at all (0mA) or
Low error current (3.6mA) on one of the outputs or
High error current (>21.0mA) on one of the outputs.
The safe signals have to be processed by a connected logical component PCS.
The voter can be a standalone voter realized in hardware and/or software or a software
voter integrated into a control system like a PLC.