Function Description - WAGO I/O-SYSTEM 750 Manual

WAGO-I/O-SYSTEM 750
750-484 2AI 4-20mA HART Ex i
7

Function Description

HART (Highway Addressable Remote Transducer) is an established variant of
digital field communication, which has been introduced as an industry standard
and which also enables multivariable field devices to be supported and used in
systems with conventional 4 mA to 20 mA technology. Typical applications are
transducers for the measurement of mechanical and electrical variables.
The HART protocol works using the FSK process (Frequency Shift Keying) in
accordance with the Bell 202 communications standard. Here, the digital signal,
which is made up of the two frequencies 1200 Hz (logic 1) and 2200 Hz (logic 0),
is sinusoidally superimposed on the analog current signal. By coding the digital
signal with zero mean value, additional information can be transmitted at the
same time without affecting the analog signal transmission. This information can
come from the field device and be intended for the process control system or for
maintenance (e.g., process variable, device status). However, information can
also be written to the field device – acyclically – for parameterization or
configuration.
Along with the simplex channel for the current signal (analog controller  field
device), the HART protocol therefore also provides a half-duplex channel for two-
way communication.
Further advantages of HART are simple construction, maintenance and
application as well as flexible data access via up to two operator control units (PC
and hand terminal). HART field devices and also HART masters are compatible
with 4-20 mA technology. HART field devices can therefore be used with non-
HART-compatible masters and vice-versa. This provides the great advantage
that the user can upgrade his system with HART modules step-by-step.
In the as-supplied state of the HART I/O module; i.e., in the default operating
mode, the HART device can be accessed directly from an IEC61131-3 program
via the I/O module. In this case, HART communication is achieved very easily by
means of the pre-prepared PLC library "WagoLibHART_0x.lib", which is provided
by WAGO as a free download.
With the simple parameterization of the HART I/O module via GSD (device
master data) or WAGO-I/O-CHECK, 4 operating modes can be selected specially
for using the HART I/O module in PROFIBUS systems, in which up to 4 HART
dynamic variables (PV, SV, TV, QV) can be incorporated in the cyclic process
image.
When using the PROFIBUS DP/V1 Coupler 750-333 or Controller 7509-833, FDT
tool routing to the DTM of the connected HART device is likewise possible in a
further operating mode in conjunction with the 759-360 PROFIBUS/HART
Gateway DTM.
Function Description
Manual
Version 1.4.0
51