Vega VEGADIF 85, Руководство по эксплуатации, Страница: 86 / 96

86
12 Supplement
VEGADIF 85 • Profibus PA
53569-EN-230814
pected in practice. It is also called maximum practical deviation or operational error.
According to DIN 16086, the total deviation F
total
is the sum of the basic deviation F
perf
and the long-
term stability F
stab
:
F
total
= F
perf
+ F
stab
The basic deviation F
perf
in turn consists of the thermal change of the zero signal and the output
span F
T
(temperature error) as well as the deviation F
Kl
:
F
perf
= √((F
T
)
2
+ (F
Kl
)
2
)
The thermal change of the zero signal and output span F
T
is specified in chapter " Technical data ".
This applies initially to the digital signal output through HART, Profibus 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
12.4 Calculation of the total deviation - Practical example
Data
Differential 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 %