Siemens SITRANS P - Manual (Page 65)

SITRANS P measuring instruments for pressure
Transmitters for gage, absolute and differential pressure, flow and level
DS III, DS III PA and DS III FF series
Technical description
2/65 Siemens FI 01 · 2009
2
■
Function
Operation of the electronics with PROFIBUS PA communica-
tion
Function diagram of the electronics
The bridge output voltage created by the sensor (1, Figure
"Function diagram of the electronics") is amplified by the instru-
ment amplifier (2) and digitized in the analog-to-digital converter
(3). The digital information is evaluated in a microcontroller, its
linearity and temperature response corrected, and converted in
a digital-to-analog converter (5) into an output current of 4 to
20 mA.
The diode circuit (10) protects against incorrect polarity.
The data specific to the measuring cell, the electronics data, and
the parameter data are stored in the two non-volatile memories
(6). The one memory is coupled to the measuring cell, the other
to the electronics. As the result of this modular design, the elec-
tronics and the measuring cell can be replaced separately from
each other.
Using the 3 input keys (8) you can parameterize the pressure
transmitter directly at the point of measurement. The input keys
can also be used to control the view of the results, the error mes-
sages and the operating modes on the digital display (9).
The HART modem (7) permits parameterization using a protocol
according to the HART specification.
The pressure transmitters with spans
≤ 63 bar measure the input
pressure compared to atmosphere, transmitters with spans
≥ 160 bar compared to vacuum.
Operation of the electronics with PROFIBUS PA communica-
tion
Function diagram of the electronics
The bridge output voltage created by the sensor (1, Figure
"Function diagram of the electronics") is amplified by the instru-
ment amplifier (2) and digitized in the analog-to-digital converter
(3). The digital information is evaluated in the microcontroller, its
linearity and temperature response corrected, and provided on
the PROFIBUS PA through an electrically isolated PA interface
(7).
The data specific to the measuring cell, the electronics data, and
the parameter data are stored in the two non-volatile memories
(6). The first memory is linked with the measuring cell, the sec-
ond with the electronics. This modular design means that the
electronics and the measuring cell can be replaced separately
from one another.
Using the three input keys (8) you can parameterize the pressure
transmitter directly at the point of measurement. The input keys
can also be used to control the view of the results, the error mes-
sages and the operating modes on the digital display (9).
The results with status values and diagnostic values are trans-
ferred by cyclic data transmission on the PROFIBUS PA. Param-
eterization data and error messages are transferred by acyclic
data transmission. Special software such as SIMATIC PDM is re-
quired for this.
I
A
, U
H
5
6
7
8
P
e
1
4 3 2
C m
M
10
0 0 00 0
0 0
9
6
1 Measuring cell sensor
2 Instrument amplifier
3 Analog-to-digital converter
4 Microcontroller
5 Digital-to-analog converter
6 One non-volatile memory each in the measuring cell and electronics
7 HART interface
8 Three input keys (local operation)
9 Digital display
10 Diode circuit and connection for external ammeter
I
A
Output current
U
H
Power supply
P
e
Input variable
Sensor
EEPROM
EEPROM
HART interface
Electronics
Measuring cell
6
8
pe
1
2
C m
M
0 0 00 0
0 0
EEPROM
EEPROM
9
6
3 4 5 7
10
12
11
1 Measuring cell sensor
2 Instrument amplifier
3 Analog-to-digital converter
4 Microcontroller
5 Electrical isolation
6 One non-volatile memory
each in the measuring cell
and electronics
7 PROFIBUS-PA interface
Sensor
Electronics
Measuring cell
PA
interface
Bus-
Master
Power
supply
unit
Coup-
ler
Power supply
PROF
IBU
S-DP
PROF
IBU
S-PA
8 Three input keys
(local operation)
9 Digital display
10 Power supply
11 DP/PA coupler or link
12 Bus master
p
e
Input variable
© Siemens AG 2008