Siemens SITRANS P - Manual (Page 29)

SITRANS P measuring instruments for pressure
Transmitters for food, pharmaceuticals and biotechnology
SITRANS P300 for gage and absolute pressure
2/29 Siemens FI 01 · 2009
2
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Design
The device comprises:
• Electronics
• Housing
• Measuring cell
Perspective view of the SITRANS P300
The housing has a screw-on cover (3), with or without an inspec-
tion window depending on the version. The electrical terminal
housing, the buttons for operation of the device and, depending
on the version, the digital display are located under this cover.
The connections for the auxiliary power UH and the shield are in
the terminal housing. The cable gland is mounted on the side of
the housing. The measuring cell with the process connection (5)
is located on the underside of the housing. Depending on the
version of the device, the measuring cell with the process con-
nection may differ from the one shown in the diagram.
■
Function
Operation of the electronics with HART communication
Function diagram of electronics
The input pressure is converted into an electrical signal by the
sensor (1). This signal is amplified by the measuring amplifier (2)
and digitalized in an analog to digital converter (3). The digital
signal is analyzed in a microcontroller (4) and corrected with re-
gard to linearity and thermal characteristics. In a digital to ana-
log converter (5) it is then converted into the output current of 4
to 20 mA. A diode circuit provides reverse voltage protection.
You can make an uninterrupted current measurement with a low-
ohm ammeter at the connection (10). The data specific to the
measuring cell, the electronic data and parameter settings are
stored in two non-volatile memories (6). The first memory is
linked with the measuring cell, the second with the electronics.
The buttons (8) can be used to call up individual functions, so-
called modes. If you have a device with a digital display (9), you
can use this to track mode settings and other messages. The ba-
sic mode settings can be changed with a computer via the HART
modem (7).
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
© Siemens AG 2008