4.4.7
How TF420 works
The functional principle is described below based on the function chart.
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①
LED
⑥
HART modem
②
Local display
⑦
Computer
③
Test terminals
⑧
Galvanic isolation
④
Feed splitter, e.g. SITRANS I100
⑨
Inputs
⑤
Load
A/D
Analog-to-digital converter
μC1
Microcontroller, on the secondary side
Figure 4-23
Function chart for SITRANS TF with SITRANS TH420
• Input
⑨
for connecting different signal sources. Section: Input (Page 201).
• This signal is converted to a digital signal in an analog-to-digital converter (A/D).
• The digital signal is evaluated in a microcontroller (μC1) on the secondary side and corrected
to match the input characteristic.
• The digital signal is transferred via the galvanic isolation
⑧
to the microcontroller (μC2) on
the primary side.
• The analog output value is calculated in the microcontroller (μC1) on the primary side. The
functional status is indicated by LED
①
and the communications data is prepared.
• The digital-to-analog converter (D/A) subsequently converts the signal into the output
current of 4 to 20 mA.
• The power supply source is located in the output signal circuit.
Description
4.4 SITRANS TF320/TF420
SITRANS TH100/TH320/TH420/TR320/TR420/TF320/TF420 with 4 to 20 mA/HART
Operating Instructions, 05/2020, A5E41864807-AB
57
