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EP31xx 71Version: 2.4
4.5 Notices on analog specifications
Beckhoff I/O devices (terminals, boxes) with analog inputs are characterized by a number of technical
characteristic data; refer to the technical data in the respective documents.
Some explanations are given below for the correct interpretation of these characteristic data.
Full scale value
An I/O device with an analog input measures over a nominal measuring range that is limited by an upper and
a lower limit (initial value and end value); these can usually be taken from the terminal/box designation. The
range between the two limits is called the measuring span and corresponds to the equation (end value -
initial value). Analogous to pointing devices this is the measuring scale (see IEC61131) or also the dynamic
range. For analog I/O devices from Beckhoff the rule is that the limit with the largest value is chosen as the
full scale value of the respective product (also called the reference value) and is given a positive sign. This
applies to both symmetrical and asymmetrical measuring spans.
Fig.58: Measuring range
For the above examples this means:
• Measuring range 0 to 10V: asymmetric unipolar, full scale value = 10V, measuring span = 10V
• Measuring range 4 to 20mA: asymmetric unipolar, full scale value = 20mA, measuring span = 16mA
• Measuring range -200 to 1370°C: asymmetric bipolar, full scale value = 1370°C, measuring span =
1570°C
• Measuring range -10 to +10V: symmetric bipolar, full scale value = 10V, measuring span = 20V
This applies equally for analog output terminals/boxes.
± Measuring error [% of the full scale value] (also: measurement error)
The relative measuring error is referenced to the full scale value and is calculated as the quotient of the
largest numerical deviation from the true value (‘measuring error’) referenced to the full scale value.
The measuring error is generally valid for the entire permitted operating temperature range, also called the
‘usage error limit’ and contains random and systematic portions of the referred device (i.e. ‘all’ influences
such as temperature, inherent noise, aging, etc.).
It always to be regarded as a positive/negative span with ±, even if it is specified without ± in some cases.
The maximum deviation can also be specified directly.
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