Operation Principle - Siemens SITRANS T3K PA 7NG3213 Manual

7NG3213
1.4

Operation principle

The measuring signal supplied by a resistance based sensor (two, three or four
wire connection), voltage based sensor or thermocouple is amplified in the input
stage. The voltage proportional to the input variable is then converted into digital
signals in an analog/digital converter. They are converted according to the sensor
characteristic in the microprocessor. Furthermore, the microprocessor interprets
the bus commands, initiates device-internal actions and provides measured
values, status and device data by electrical isolation on the bus.
Sensor
RTD
TC
¡
I
Analog-digital converter
¡
Microprocessor
©
Electrical isolation
¢
PA interface
£
Power supply
¤
DP/PA coupler or DP/PA link
¥
Bus master
¦
Figure 1 Block diagram function of the SITRANS T3K PA
The SITRANS T3K PA contains the following integrated device protection
functions:
D Electrical current limiting:
Avoids bus overloading in the event of a fault; the data traffic of the other,
undisturbed users is maintained
D Reverse polarity protection:
Enables any conenction of the bus lines
D EMC filter
Prevents malfunctions in the case of electromagnetic interference
70
SITRANS T3K
©
¢
μP
#
Power Supply
¤
£
PA-
Inter-
PROFI-
face
BUS-PA
Instruction Manual
Power
supply
Coup--
PROFIBUS-
ler
DP
¥
¦
Bus
master
SITRANS T3K PA
C79000-B7174-C55-03