Function Description
Operating Manual PNOZ m EF 4AI
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}
Sensor's measuring range: 0 ... 100 °C at 4 ... 20 mA.
Resolution of the sensor: 100 °C / (20 – 4 mA) =
6.25 °C per mA
.
The overall accuracy in °C is therefore: 0.5 mA * 6.25 °C per mA =
3.125 °C
.
This overall accuracy must be considered when defining monitored limit values in the user
program.
For example, if a hazardous situation should arise at a temperature above 80 °C, a safe re-
action must occur in the user program at a temperature above 80 °C - 3.125 °C =
76.875 °C.
Example for calculating the overall measuring accuracy with 2-channel operation
With 2-channel operation, two inputs and two sensors must be used, as well as the
Plaus-
ibility test
function.
The overall accuracy in % is calculated by adding the following values:
}
Empirically established tolerance
Instead of the module's safety-related accuracy, an empirically established tolerance is
used with 2-channel operation.
Enter in the PNOZmulti Configurator in the element
Plausibility
a percentage tolerance
at which availability is still maintained.
This tolerance value defines the maximum permitted deviation between the two analogue
input signals.
In the example, a tolerance of
2 %
has been determined.
If as set tolerance is exceeded, the analogue value is signalised as invalid. For availability
reasons we therefore recommend that you use a slightly higher value for the tolerance
than the empirically established deviation.
For the example, a tolerance of
3 %
was therefore set for the plausibility monitoring.
}
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
needs 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 value of
0.5 %
is assumed for
this example (in relation to the overall measuring range of 0 … 20 mA).
Calculation of the monitored limit values, taking into account the overall accuracy:
}
Overall accuracy in
%
:
3 % + 0.5 % + 0.5 %
= 4 %
.
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 * 4 % =
1 mA
}
Sensor's measuring range: 0 ... 500 mbar at 4 ... 20 mA.
Resolution of the sensor: 500 mbar / (20 – 4 mA) =
31.25 mbar per mA
.
The overall accuracy in mbar is therefore: 1 mA * 31.25 mbar per mA =
31.25 mbar
.
