Rosemount 1199, Справочное руководство

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Reference Manual
00809-0100-4002, Rev BB
November 2012
2-3
Rosemount 1199
Figure 2-3. Back pressure on
diaphragm causing error
NOTE
Seal temperature effects decrease as seal size increases.
Head Temperature
Effects (Ambient
Temperature Error)
Head temperature effect is due to the change in specific gravity of the fill fluid
caused by a change in ambient temperature. When installed, the weight of the
fill fluid will produce an initial pressure read by the transmitter, equalling the
height between the high and low connection taps multiplied by the fill fluid's
specific gravity. As ambient temperature changes, the fill fluid specific gravity
will change causing the weight of the fill fluid to change, thus changing the
pressure read by the transmitter. Head effect will be seen in both
Tuned-System
™
Assemblies and Balanced System Assemblies and will have
the same impact on the transmitter regardless of where the transmitter is
mounted.
System Time Response
The time response of a system is based on the type of transmitter, its sensor
range, the length and inner diameter (ID) of the capillary, and the viscosity of
the fill fluid (which is directly affected by the process and ambient
temperatures). These factors all play a role in the overall performance of any
seal system. Below is an example including 3 applications with the same
process and ambient temperatures. The difference is one system is balanced
(equal lengths of capillary),
the other two are tuned systems (high pressure
side is a direct mount with low pressure side connected via capillary) but one
has a 0.040 in. capillary ID size and the other has the 0.075 in. capillary ID
size.
HEAT
HEAT
HEAT
2 in.
1.7 inH2O
(43 mmH2O)
3 in.
0.5 inH2O
(13 mmH2O)
1 ½ in.
12.1 inH2O
(307 mmH2O)