VEGA VEGABAR 64 4 … 20 mA_HART User Manual
Page 49
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
64
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
VEGABAR
64 • 4 … 20
mA/HART
49
8 M
aintenance and fault rectification
27525
-
EN
-081209