Siemens SITRANS P DS III - Page 99

Operator control functions via PROFIBUS
7.1 Communications structure for PROFIBUS PA
SITRANS P DS III with PROFIBUS PA
Operating Instructions, 06/2013, A5E00053276-07
99
Functional principle
The
raw pressure value
first passes through a
calibration
. The resulting
cleaned-up pressure
value
is checked for
sensor limits
. Any violation of the limits results in status "Bad" and a
diagnostic error of "error collecting measured value". The cleaned-up pressure value is
stored in
SEC 1
.
Then, it is subjected to a
normalization
, where the input signal is expressed in the range 0 to
10 (percentage/100). The
normalized pressure value
is stored in
SEC 2
.
Afterwards, depending on the measurement task, it is fed through one of four different
linearization types
.
Scaling
uses the preset
working range
(minimum and maximum values)
to determine the normalized and linearized measured value (pressure, height, or volume) of
the actual process variable. This is stored in
PRIM
.
By means of a
multiplication
with the
density
the volume is used to compute the
mass
. This
is stored in
SEC 3
.
The
temperature value of the pressure sensor
is available in the "
temperature
" parameter.
See also
Acyclic data transfer (Page 164)