How Hart Works - Siemens SIMATIC ET 200SP HA Manual

HART function

6.1 How HART works

6.1 How HART works
Introduction
The HART protocol describes the physical form of the transfer: transfer procedures, message
structure, data formats and commands.
HART signal
The figure below shows the analog signal with the modulated HART signal (FSK method),
which consists of sine waves of 1200 Hz and 2200 Hz and has a mean value of 0. It can be
filtered out using an input filter so that the original analog signal is available again.
20 mA
1
4 mA
0
Figure 6-1
①
②
K
A
HART communication
The I/O module processes the HART communication in parallel operation, that is, all channels
simultaneously.
With enabled HART operation, the I/O module automatically sends HART commands to the
connected field devices. These commands always alternate with any pending external HART
26
+0,5 mA
-0,5 mA
K
A
K
The HART signal
Analog signal
Time (seconds)
Command
Response
0
1200 Hz 2200 Hz
"1" "0"
A
K
A
2
Analog Input Module AI 16xI 2-wire HART HA ( 6DL1134-6TH00-0PH1)
K
A
Manual, 11/2017, A5E39408968-AB