VEGA VEGABAR 54 Profibus PA - Manual (Page 39)

39
8 Maintenance and fault rectification
VEGABAR 54 • Profibus PA
36729-EN-130321
Depending on the reason for the fault and the measures taken, the
steps described in chapter "Set up" may have to be carried out again.
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 50 °C, reference temperature 20 °C
Calculation ΔT: ΔT = 50 °C - 20 °C = 30 K
VEGABAR 54, with measuring range 25 bar, version 0.2 %
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
= (0.1 %/10 K x ΔT)
F
Kl
= 0.2 %
F
perf
= √((0.1 %/10 K x 30 K) 2 + (0.2 %) 2 )
F
perf
= 0.36 %
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
= 0.36 % + 0.31 % = 0.67 %
Total deviation digital output signal absolute:
F
total
= 0.67 % x 8 bar/100 % = 53.6 mbar
Basic accuracy analogue output signal in percent:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 + (F
a
) 2 )
Reaction after fault recti-
fication
Total deviation
Example