VEGA VEGABAR 65 4 … 20 mA_HART - Manual (Page 50)

8.3 Calculation of total deviation (similar to
DIN 16086)
T he 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
K l
)
2
)
W ith analogue output, the error of the current output F
a
is also added.
F
perf
= √((F
T
)
2 + (F
K l
)
2 + (F
a
)
2
)
W ith:
l F
total
: T otal deviation
l F
perf
: B
asic accuracy
l F
stab
: L ong-term drift
l F
T
: T emperature coefficient (influence of medium or ambient
temperature)
l F
K l
: D eviation
l F
a
: E rror current output
P
ressure measurement in the pipeline 8 bar (800 KPa)
P roduct temperature 50 °C, hence within the compensated range
VEGABAR 65 with measuring range 25 bar
C alculation 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
K l
)
2
)
F
T
= (0.05 % + 0.1 % x TD)
F
K l
= 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
50 VEGABAR 65 • 4 … 20 mA/HART
8 M aintenance and fault rectification
27531
-EN
-081209