Vega VEGADIF 85 - Calculation of the Total Deviation - Practical Example

89
11 Supplement
VEGADIF 85 • Modbus and Levelmaster protocol
53571-EN-230814
F
perf
=√((F
T
)
2
+(F
Kl
)
2
)
The thermal change of the zero signal and output span F
T
isspeciedinchapter"Technical data".
ThisappliesinitiallytothedigitalsignaloutputthroughHART,ProbusPA,FoundationFieldbusor
Modbus.
With 4 … 20 mA output, the thermal change of the current output F
a
must be added:
F
perf
=√((F
T
)
2
+(F
Kl
)
2
+(F
a
)
2
)
To provide a better overview, the formula symbols are listed together below:
•
F
total
: Total deviation
•
F
perf
: Basic deviation
•
F
stab
: Long-term stability
•
F
T
: Thermal change of zero signal and output span (temperature error)
•
F
Kl
: Deviation
•
F
a
: Thermal change of the current output
•
FMZ: Additional factor measuring cell version
•
FTD: Additional factor Turn down
11.8 Calculation of the total deviation - Practical example
Data
Dierentialpressure250 mbar(25KPa),mediumtemperatureonthemeasuringcell60°C
VEGADIF 85 with measuring range 500 mbar
The required values for the temperature error F
T
, deviation F
Kl
and long-term stability F
stab
are avail-
able in the technical data.
1. Calculation of the Turn down
TD=500mbar/250mbar
TD= 2 : 1
2. Determination temperature error F
T
Measuring range -10 … +60 °C / +14 … +140 °F -40 … -10 °C / -40 … +14 °F und
+60 … +85 °C /+140 … +185 °F
10mbar(1kPa)/0.145psi <±0.15%+0.20%xTD <±0.4%+0.3%xTD
30mbar(3kPa)/0.44psi <±0.15%+0.10%xTD <±0.2%+0.15%xTD
100mbar(10kPa)/1.5psi <±0.15%+0.15%xTD <±0.15%+0.2%xTD
500mbar(50kPa)/7.3psi
<±0.15%+0.05%xTD
<±0.2%+0.06%xTD
3bar(300kPa)/43.51psi
16bar(1600kPa)/232.1psi <±0.15%+0.15%xTD <±0.15%+0.20%xTD
F
T
=0.15%+0.05%xTD
F
T
=0.15%+0.1%
F
T
=0.25 %