HART bus (
Highway Addressable Remote Transducer) is designed for digital serial data transfer over a standard 4-20 mA analog current loop and is used to transmit measured values from intelligent sensors, and to adjust, calibrate and monitor them.
The
HART bus uses the master-slave method to access the communication channel. The master sends commands and data to (up to 15) slaves and processes their responses.
Examples of concrete meters:
HART Configurator, PRelectronic 5335
MH-02, JSP, spol. s r.o.
HART modems
The
HART protocol is used by meters via a special interface and therefore a hardware Modem is necessary to convert the communication from
HART to
RS232.
For example the following modems have been tested:
Modem MH-02, manufactured by JSP, spol. s r.o.
Modem Configurator, manufactured by JSP, spol. s r.o.
HART converter
- Converter
Pretop 5335, PRelectronic
The main task of the application layer is to define commands and responses.
HART commands are divided into Universal Commands, Common-Practice Commands and Device Specific Commands. Universal commands must be implemented in all
HART devices. Commonly used and specific commands are dependent on the type of the device and may not be available.
The universal commands are as follows:
0: reading a unique identifier
1: reading a primary variable
2: reading loop current and percentage of the range
3: reading dynamic variables and loop current
6: writing the polling address
7: reading the current loop settings
8: reading the classification of dynamic variables
9: reading the device variables with status
11: reading the unique identifier associated with the tag
12: reading the dynamic variables and loop current
13: reading the tag, descriptor and date
14: reading the converter information
15: reading the device information
16: reading the final serial number
up to 48.
Command 0 sends a short slave address with polling addresses zero to fifteen. If a response is received to the request, then a slave with that address exists. The response received from the slave contains a long (unique) address, which is further used to compose other messages.
See
Preconfiguration "PmChar Communication protocol HART".