Siemens SITRANS P Brochure & Specs page 156
Measuring instruments for pressure
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- Operating instructions manual (280 pages) ,
- Compact operating instructions (94 pages) ,
- Compact operating instructions (98 pages)
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SITRANS P measuring instruments for pressure
Remote seals for transmitters and pressure gages
Technical description
Calculation of the temperature error
The following equation is used to calculate the temperature er-
ror:
dp = (
–
) f
RS
Cal
RS
2
dp
Additional temperature error (mbar)
Temperature on remote seal diaphragm (generally
RS
corresponds to temperature of medium)
Calibration (reference) temperature (20 °C (68 °F))
Cal
f
Temperature error of remote seal
RS
Ambient temperature on the capillaries
Cap
l
Capillary length
Cap
f
Temperature error of capillaries
Cap
Ambient temperature on pressure transmitter
TR
f
Temperature error of the oil filling in the process
PF
flanges of the pressure transmitter
Example of temperature error calculation
Existing conditions
SITRANS P pressure transmitter for
differential pressure, 250 mbar, set
to 0 ... 100 mbar, with DN 80 remote
seal diaphragms without tube, dia-
phragm made of stainless steel,
mat. No. 1.4404/316L
Capillary length
Capillaries fitted on both sides
Filling liquid silicone M5
Process temperature
Temperature on the capillaries
Temperature on pressure transmit-
ter
Calibration temperature
Required
Additional temperature error of
remote seals
Calculation
in mbar
dp = (100 °C – 20 °C) 0.1 mbar/10 K + (50 °C – 20 °C) 6 m
0.07 mbar/(10 K m) + (50 °C – 20 °C) 0.07 mbar/10 K
dp = 0.8 mbar + 1.26 mbar + 0.21 mbar
in psi
dp = (212 °F – 68 °F) 0.0014 psi/10 K + (112 °F – 68 °F) 19.7 ft
0.001 psi/(10 K 3.28 ft) + (112 °F – 68 °F) (0.001 psi/10 K)
dp = 0.012 psi + 0.018 psi + 0.003 psi
Result
dp = 2.27 mbar (0.033 psi) (corresponds to 2.27% of set span)
Note
The determined temperature error only applies to the error resulting
from connection of the remote seal.
The transmission response of the respective transmitter is not included
in this consideration.
It must be calculated separately, and the resulting error added to the
error determined above from connection of the remote seal.
2/156
Siemens FI 01 · 2009
+ (
–
) l
f
+ (
Cap
Cal
Cap
Cap
TR
f
= 0.1 mbar/10 K
RS
(0.0014 psi/10 K)
l
= 6 m (19.7 ft)
Cap
f
= 0.07 mbar/(10 K m
Cap
(0.001 psi/(10 K m
f
= 0.07 mbar/10 K
PF
(0.001 psi/10 K)
= 100 °C (212 °F)
RS
= 50 °C (122 °F)
Cap
= 50 °C (122 °F)
TR
= 20 °C (68 °F)
Cal
dp
© Siemens AG 2008
Dependence of temperature error on diaphragm material
The temperature errors listed in the previous table are based on
the use of stainless steel as the diaphragm material. If other dia-
phragm materials are used, the temperature errors change as
–
) f
Cal
PF
follows:
Diaphragm material
Stainless steel
Hastelloy C4, mat. No. 2.4610
Hastelloy C276, mat. No. 2.4819
Monel 400, mat. No. 2.4360
Tantalum
Titanium
PTFE coating on stainless steel dia-
phragm
ECTFE coating or PFA coating on
stainless steel diaphragm
Gold coating on stainless steel dia-
phragm
Maximum temperature of medium
The following maximum temperatures of the medium apply de-
pending on the material of the wetted parts:
)
Cap
Material
))
Cap
Stainless steel, 316L
PTFE coating
ECTFE coating
PFA coating
Hastelloy C4, mat. No. 2.4610 200
Hastelloy C276, mat. No.
2.4819
Monel 400, mat. No. 2.4360
Tantalum
Maximum capillary length for diaphragm seals (guidance
values)
Nom. diam.
DN 25
(1 inch)
DN 32
(1¼ inch)
DN 40
(1½ inch)
DN 50
(2 inch)
DN 65
(2½ inch)
DN 80
(3 inch)
DN 100
(4 inch)
DN 125
(5 inch)
Change in temperature error of
remote seal
Increase in values by
See previous tables
50%
50%
60%
50%
50%
80%
100%
40%
p
< 1 bar
p
> 1 bar
abs
abs
(14.5 psi)
(14.5 psi)
°C
(°F)
°C
(°F)
200
(392)
400
(662)
200
(392)
260
(500)
100
(212)
150
(302)
200
(392)
260
(500)
(392)
260
(500)
200
(392)
400
(662)
200
(392)
400
(662)
200
(392)
300
(572)
Max. length of capillary
Diaphragm seal
Clamp-on seal
m
(ft)
m
2.5
(8.2)
2.5
2.5
(8.2)
2.5
4
(13.1)
6
(19.7)
6
(19.7)
10
8
(26.2)
10
10
(32.8)
10
(32.8)
10
(32.8)
10
(32.8)
10
(32.8)
-
-
(ft)
(8.2)
(8.2)
(32.8)
(32.8)
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