VEGA VEGABAR 66 Profibus PA - climate compensated - Manual (Page 49)

49
8 Maintenance and fault rectification
VEGABAR 66 • Profibus PA - climate compensated
36792-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 1.5 mWs
Ambient temperature 40 °C, product temperature 10 °C
VEGABAR 66 with measuring range 0.2 bar
Deviation < 0.1 %
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
= (0.15 + 0.4 x TD) %
F
Kl
= 0.1 %
F
perf
= √((0.15 % + 0.4 % x 1.4) 2 + (0.1 %) 2 )
F
perf
= 0.72 %
Total deviation digital output signal in percent:
F
total
= F
perf
+ F
stab
F
stab
= (0.1 % x 1.4)/year
F
stab
= 1.4 %
F
total
= 0.72 % + 1.4 % = 2.12 %
Total deviation digital output signal absolute:
F
total
= 2.12 % x 147 mbar/100 % = 3.11 mbar = 31.77 mm
Basic accuracy analogue output signal in percent:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 + (F
a
) 2 )
F
T
= (0.15 + 0.4 x TD) %
F
Kl
= 0.1 %
F
a
= 0.15 %
Total deviation
Example