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5.4.2
Measurement error/measurement deviation/measurement
uncertainty, output uncertainty
Analog output
The following information also applies analogously to the output end value of analog output devices.
The relative measuring error as a specification value of a Beckhoff analog device is specified in % of the
nominal FSV (output end value) and calculated as the quotient of the numerically largest probable deviation
from the true measured value (output value) with respect to the FSV (output end value):
It should be noted here that the "true measured value" cannot be determined with infinite accuracy either, but
can only be determined via reference devices with a higher expenditure of technology and measuring time
and thus a significantly lower measurement uncertainty.
The value therefore describes the result window in which the measured value determined by the device
under consideration (Beckhoff analog device) lies with a very high probability in relation to the "true value".
Thus, colloquially, this is a "typical" value (typ.); this expresses that the vast statistical majority of values will
be within the specification window, but in rare cases there may/will be deviations outside the window.
For this reason, the term "measurement uncertainty" has become established for this window, since "error" is
now used to refer to known disturbance effects that can generally be systematically eliminated.
The uncertainty of measurement must always be considered in relation to potential environmental influences:
• invariable electrical channel properties such as temperature sensitivity,
• variable settings of the channel (noise via filters, sampling rate, ...).
Measurement uncertainty specifications without further operational limitation (also called "service error limit")
can be assumed as a value "over everything": entire permissible operating temperature range, default
setting, etc.
The window is always to be understood as a positive/negative span with "±", even if occasionally indicated
as a "half" window without "±".
The maximum deviation can also be specified directly.
Example: measuring range 0...10 V (FSV = 10 V) and measurement uncertainty < ± 0.3%
maximum usual deviation is ± 30 mV in the permissible operating temperature range.
Lower measurement uncertainty possible
If this specification also includes the temperature drift, a significantly lower measuring error can
usually be assumed in case of a constant ambient temperature of the device and thermal
stabilization after a user calibration.
EL3692
Version: 3.1
Commissioning
→ the expected
FSV
123
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