60
9 Supplement
WIKA Operating Instructions - Process pressure transmitter IPT-2x
This applies for a digital signal output through HART, Profibus PA or Foundation Fieldbus.
With a 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
9.3 Practical example
Data
Level measurement in a small vessel, 500 mm height corresponds to 0.049 bar (4.9 KPa), superim-
posed pressure 0.35 bar (35 KPa), medium temperature 40 °C
IPT-2x Master and slave sensor each with nominal measuring range 0.4 bar (40 KPa), deviation
< 0.1 %, process fitting G1 (piezoresistive measuring cell)
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 = 0.4 bar/0.049 bar, TD = 8.2 : 1
2. Determination temperature error F
T
The temperature error F
T
consists of the basic temperature error F
TBasis
, the additional factor meas-
uring cell F
MZ
and the additional factor Turn Down F
TD
.
(TD 1:1)
T / °C
50 °C
40 °C
20 °C
10 °C
-40 °C
100 °C
150 °C
0,15
-0,15
-0,3
-0,45
-0,6
-0,75
-0,9
0,3
0,45
0,6
0,75
0,9
F/
%
TBasis
Fig. 34: Determination of the basic temperature error for the above example: F
TBasis
= 0.15 %
