VEGA VEGABAR 66 Profibus PA - Manual (Page 48)

48
8 Maintenance and fault rectification
VEGABAR 66 • Profibus PA
36739-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
Level measurement 1500 mmWs
Product temperature 40 °C, reference temperature 20 °C
VEGABAR 66 with measuring range 0.2 bar
Deviation < 0.1 %
Calculation ΔT: ΔT = 40 °C - 20 °C = 20 K
Calculation of the set Turn Down:
TD = 200 mbar/147 mbar, TD = 1.4
Basic accuracy digital output signal in percent:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 )
F
T
= 0.05 %/10 K x TD
F
Kl
= 0.1 %
F
perf
= √((0.05 %/10 K x 20 K x 1.4) 2 + (0.1 %) 2 )
F
perf
= 0.17 %
Total deviation digital output signal in percent:
F
total
= F
perf
+ F
stab
F
stab
= 0.1 %/year x TD
F
stab
= 0.1 %/year x 1.4
F
stab
= 0.14 %
F
total
= 0.17 % + 0.14 % = 0.31 %
Total deviation digital output signal absolute:
F
total
= 0.35 % x 147 mbar/100 % = 0.46 mbar = 4.7 mm
Basic accuracy analogue output signal in percent:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 + (F
a
) 2 )
F
T
= 0.05 %/10 K x TD
Total deviation
Example