VEGA VEGABAR 55 Foundation Fieldbus - Manual (Page 41)

41
8 Maintenance and fault rectification
VEGABAR 55 • Foundation Fieldbus
36736-EN-130321
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, hence within the compensated range
VEGABAR 55 with measuring range 10 bar
Calculation 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
Kl
) 2 )
F
T
= (0.05 % + 0.1 % x TD)
F
Kl
= 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
Basic accuracy analogue output signal in percent:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 + (F
a
) 2 )
F
T
= (0.05 % + 0.1 % x TD)
F
Kl
= 0.075 %
F
a
= 0.15 %
F
perf
= √((0.05 % + 0.1 % x 1.25) 2 + (0.075 %) 2 + (0.15 %) 2 )
F
perf
= 0.24 %
Total deviation analogue 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 %
Example