SFAM
34
Festo – SFAM – 2017-09c English
According to the specification the following apply for nominal conditions (6 bar, 0.6 MPa, 23 °C):
–
Accuracy range: ±3 %FS
–
Accuracy of zero point: ±0.3 %FS.
–
(in example: FS = 1000 l/min)
The overall error during nominal conditions is made up of both of these error variables, which in the
following will be considered separately.
a) Range error
A range error of the measurement signal (= error in the slope of the characteristic curve) has a stronger
effect the larger the measurement value is (
è
Fig. 12). A range error can be designated a sensitivity or
slope error.
z
x = measured variable (flow rate)
y = measurement value (display)
z = display value error sought
y
x
Fig. 12
Range error
The maximum error results from the largest full-scale measured value (in the example
FS = 1000 l/min). According to the specification, the error is specified at ±3 %FS.
The maximum error is calculated as follows:
±3 %FS = ±3 % x 1000 l/min =±3/100 x 1000 l/min = ±30.00 l/min
If a measurement value of 600 l/min is displayed, the maximum range error is calculated as follows:
±30 l/min × (600 l/min)/(1000 l/min)= ±18 l/min
Because of the range error, with a display of 600 l/min at the sensor, the actual flow rate through the
sensor values can have values in the range 582 … 618 l/min.
Along with the range error, the zero point error must still be taken into account.
b) Zero point error
A zero point error in the measurement signal affects every point of the characteristic curve equally,
which means that it is independent of the measurement value considered (
è
Fig. 13).
