VEGA VEGABAR 65 Foundation Fieldbus - Manual (Page 48)

8 .3 Calculation of total deviation (similar to
DIN 16086)
The total deviation F
total
according to DIN 16086 is the sum of basic
accuracy F
perf
and longterm stability F
stab
. F
total
is also called
maximum practical deviation or utility error.
F
total
= F
perf
+ F
stab
F
perf
= √((F
T
)
2 + (F
Kl
)
2
)
With analogue output, the error of the current output F
a
is also added.
F
perf
= √((F
T
)
2 + (F
Kl
)
2 + (F
a
)
2
)
With:
l F
total
: Total deviation
l F
perf
: Basic accuracy
l F
stab
: Long-term drift
l F
T
: Temperature coefficient (influence of medium or ambient
temperature)
l F
Kl
: Deviation
l F
a
: Error current output
Pressure measurement in the pipeline 8 bar (800 KPa)
Product temperature 50 °C, hence within the compensated range
VEGABAR 65 with measuring range 25 bar
Calculation of the set Turn Down: TD = 10 bar/8 bar, TD = 1.25
Basic accuracy digital output signal in percent:
F
perf
= √((F
T
)
2 + (F
Kl
)
2
)
F
T
= (0.05 % + 0.1 % x TD)
F
Kl
= 0.075 %
F
perf
= √((0.05 % + 0.1 % x 1.25) 2 + (0.075 %) 2
)
F
perf
= 0.19 %
Total deviation digital output signal in percent:
F
total
= F
perf
+ F
stab
F
stab
= (0.1 % x TD)/year
F
stab
= (0.1 % x 1.25)/year
F
stab
= 0.125 %
F
total
= 0.19 % + 0.125 % = 0.315 %
Total deviation digital output signal absolute:
F
total
= 0.315 % x 8 bar/100 % = 25.2 mbar
Total deviation
Example
48 VEGABAR 65 • Foundation Fieldbus
8 Maintenance and fault rectification
28260
-EN
-090522