Siemens MS Series, Инструкция по эксплуатации, Страница: 77 / 130

SITRANS P, MS series
77
C79000-B5674-C40-04
Technical Description
1.2.2 How it works
The following section describes how the transmitter works up to block diagram level.
The pressure p
e
is fed through the process connection (2, Figure 5, p. 77) of the mea-
suring cell (1). The pressure is transmitted to a silicone pressure sensor (5) through
the diaphragm (3) and the liquid filling (4) which distorts its measuring diaphragm.
The resistance of four piezo-resistors in bridge circuit in the measuring diaphragm
changes as a result. This change in resistance generates an output voltage in the
bridge circuit that is proportional to the input pressure. This voltage is converted into
a digital signal by a measuring amplifier (6) in an analog-digital converter (7). A mi-
crocontroller (8) evaluates the signal, corrects it with respect to linearity and temper-
ature before passing it on to a digital-analog converter (9) which converts it into the
4 to 20 mA output current.
Data specific to the measuring cell and transmitter parameters are stored in a non-
volatile memory (10).
The transmitters with measuring spans < 63 bar measure the input pressure against
atmosphere, the transmitters with measuring spans
≥
160 bar against vacuum.
The transmitter can be parameterized at the measuring point conditionally by the two
pushbuttons (12) on the inside. The HART® modem (11) enables parameterization
by a protocol according to HART® specifications. The digital indicator (13) is option-
al.
Figure 5 SITRANS P, MS series transmitter for pressure, function diagram
A
D
5
2
3
4
6 7
8 9
12
13
D
A
1
10
11
p
e
14
1 Measuring cell
2 Process connection
3 Diaphragm
4 Liquid filling
5 Silicone pressure sensor
6 Measuring amplifier
7 Analog-digital converter
8 Microcontroller
9 Digitalanalog converter
10 Non-volatile memory (EEPROM)
11 HART® modem
12 Two inside pushbuttons
13 Digital indicator (option)
14 Connection for external ammeter
I
A
Output current
U
H
Auxiliary power
p
e
Input variable pressure