4.1.3
How TH100 works
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
RTD Pt100
⑥
µC
Microcontroller: Arithmetic func‐
tions and saving of all parameters
②
EM
C_
1
Input stage with protection compo‐
nents
⑦
D/A
Digital-to-analog converter
③
Ic
Constant current source
⑧
Power supply (U
aux
)/ output current (I
out
)
④
MU
X
Multiplexer
⑨
EMC
_2
Output stage with protection compo‐
nents
⑤
A/D Analog-to-digital converter
⑩
U
ref
Voltage converter, current converter,
constant voltage source, and refer‐
ence voltage source
Figure 4-2
Function chart for SITRANS TH100
The signal delivered by an RTD Pt100 (two-wire, three-wire, four-wire system) is amplified in the
input stage. The voltage that is 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.
Description
4.1 SITRANS TH100
SITRANS TH100/TH320/TH420/TR320/TR420/TF320/TF420 with 4 to 20 mA/HART
Operating Instructions, 05/2020, A5E41864807-AB
33
