VEGA VEGABAR 54 Profibus PA - climate compensated - Manual (Page 41)

41
8 Maintenance and fault rectification
VEGABAR 54 • Profibus PA - climate compensated
36790-EN-130321
8.3 Calculation of total deviation (according 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 the analogue signal output there is also the error of the current
output F
a
.
F
perf
= √((F
T
) 2 + (F
Kl
) 2 + (F
a
) 2 )
With:
•
F
total
: Total deviation
•
F
perf
: Basic accuracy
•
F
stab
: Long-term drift
•
F
T
: Temperature coefficient (influence of medium or ambient
temperature)
•
F
Kl
: Deviation
•
F
a
: Error current output
Pressure measurement in the pipeline 8 bar (800 KPa)
Product temperature 10 °C, reference temperature 20 °C
Calculation ΔT: ΔT = 20 °C - 10 °C = 10 K
VEGABAR 54 climate compensated, with measuring range 25 bar
Calculation of the set Turn Down: TD = 25 bar/8 bar, TD = 3.1
Basic accuracy digital output signal in percent:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 )
F
T
= (0.02 + 0.03 x TD)%/10 K
F
Kl
= 0.25 %
F
perf
= √((0.02 + 0.03 x 3.1)%/10 K x10 K) 2 + (0.25 %) 2 )
F
perf
= 0.27 %
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 3.1)/year
F
stab
= 0.31 %
F
total
= 0.27 % + 0.31 % = 0.58 %
Total deviation digital output signal absolute:
F
total
= 0.58 % x 8 bar/100 % = 46.4 mbar
Basic accuracy analogue output signal in percent:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 + (F
a
) 2 )
F
T
= (0.02 + 0.03 x TD)%/10 K
F
Kl
= 0.25 %
F
a
= 0.15 %
Total deviation
Example