Siemens SITRANS TH100, Руководство по эксплуатации

Страница: 13 / 50

Description
3.4 Mode of operation
SITRANS TH100
Operating Instructions, 06/2010, A5E00331168-02
13
3.4 Mode of operation
The following function block diagram clarifies the transmitter's mode of operation:
(0&B
3W
08;
$'
'$
w&
8 ,
8
UHI
(0&B P$
8
UHI
,F
8
DX[
,
out
①
Pt100 resistance thermometer
②
Input stage with protection components
③
Constant current source
④
Multiplexer
⑤
Analog-to-digital converter
⑥
Microcontroller: arithmetic functions and
saving of all parameters
⑦
Digital-to-analog converter
⑧
Auxiliary power supply (U
aux
)/ output
current (I
out
)
⑨
Output stage with protection components
⑩
Voltage converter, current converter,
constant voltage source, and reference
voltage source
Figure 3-2 Function block diagram SITRANS TH100
Mode of operation of the transmitter
The signal delivered by a Pt100 resistance thermometer (two-wire, three-wire, four-wire
system) is amplified in the input stage. The voltage proportional to the input variable is then
converted into digital signals by a multiplexer in an analog-to-digital converter. These are
converted in the microcontroller in accordance with the sensor characteristic and further
data, e.g. measuring range or damping.
The signal prepared in this manner is then converted in a digital-to-analog converter into a
load-independent direct current of 4 to 20 mA.
The input and output circuits are each protected against electromagnetic interference
through the use of EMC filters.