MULTIPLEXER AS THE PRIMARY I/O SYSTEM
PARALLEL MONITORING WITH A MULTIPLEXER
HART-compatible multiplexers are ideal for users who want to interface with a large number of HART devices. Multiplexers can be modular and are capable of supporting both point-to-point and all-digital (multidrop) HART communication modes. Communication between a multiplexer and a host application depends on the multiplexer capabilities (e.g., RS232C, RS485, Modbus, and TCP/IP Ethernet).
When installing
HART multiplexer systems, the following capabilities should be considered:
Number of HART channels supported
Number of HART channels that share a HART modem
Burst mode support
Multidrop support
Method of communication with the host computer or control system
HART multiplexers can be used as the primary I/O front end for a
HART-based control or monitoring system (Figure 10). Typically,
a PC acts as the host, providing the human-machine interface and performing other high-level functions. The multiplexer continuously monitors the field devices, reports the current readings and
instrument status to the host, and passes HART commands from the host computer to the field devices.
Figure 10: HART Multiplexer as the Primary I/O System
When a traditional 4–20mA control system is using the analog signals for measurement and control outputs, a HART multiplexer can be added to the network to gain access to the digital HART signal. Using a multiplexer enables a supervisory computer to monitor diagnostics and device status, access configuration information, and read any additional process inputs or calculations not provided by the 4–20mA signal.
