Function Description
Operating Manual PNOZ m EF 4AI
1004650-EN-02
| 13
NOTICE
For SIL 3 applications, set a maximum permitted deviation between the
measured values of both input signals (tolerance) in the PNOZmulti Config-
urator. A tolerance is only entered to balance out the imprecision of the sig-
nal recording, the encoder and the analogue input module. To maintain
safety, the tolerance should be set as low as possible. Please note that the
maximum safety-related measurement error for the overall system
is
composed of the following measurement errors:
Error during signal recording
+ Sensor measurement error
+ Max. measurement error in the event of an error at the module
Measures
for achieving process safety [
13]
To ensure that your application switches off safely in the event of a critical
process variable, the configuration of the range limits/threshold values must
be increased/decreased.
4.1.1
Measures for achieving process safety
The module will detect internal module errors. Sensor errors and wiring errors can be de-
tected using the function
Working range monitoring
.
Please note that the overall accuracy must be considered when defining monitored limit val-
ues in the user program. The calculation of the overall accuracy is described in the follow-
ing examples
Example for calculating the overall measuring accuracy with 1-channel operation
The overall accuracy in % is calculated by adding the following values:
}
Module's safety-related accuracy of
1 %
(see
Technical details [
34]
).
}
Module's measuring accuracy
This value is calculated by adding all deviations from the measuring range limit value
(see
Technical details [
34]
).
The value
Greatest transient deviation during el. interference test
need only be con-
sidered in environments with strong EMC interference.
A measuring accuracy of
0.5 %
is assumed for this example.
}
Sensor's measuring accuracy
This value is taken from the sensor's technical details.
A measurement accuracy of
0.5 %
is assumed for this example (in relation to the overall
measuring range of 0 … 25 mA).
Calculation of the monitored limit values, taking into account the overall accuracy:
}
Overall accuracy in
%
:
1 % + 0.5 % + 0.5 %
= 2 %
.
The overall accuracy refers to the overall measuring range of 0 ... 25 mA
}
Overall accuracy in
mA
in relation to the overall measuring range:
25 mA * 2 % =
0.5 mA
