Test Report from Engineers at Smar

Thursday, April 07, 2005



Q3 2002 — MDS iNET 900™ Meets Requirements of FOUNDATION™ Fieldbus HSE and Modbus/TCP
A test to verify Microwave Data Systems (MDS) iNET 900 wireless Ethernet access point connectivity for industrial communication protocols was carried out successfully. The test was conducted jointly between engineers from Smar and MDS. The test was carried out at a short distance. However, the test was not to verify distance, but to ensure that the radio link meets the requirement of FOUNDATION Fieldbus HSE and Modbus/TCP.

Background
The MDS iNET 900 is a long range, industrial wireless IP/Ethernet solution. It allows customers to gather information and operate the process and devices over radio using Ethernet. This includes mission-critical, revenue-generating data from fixed assets such as oil and gas wells, compressor stations, pipelines, fluid storage tanks and unmanned platforms. In addition to process control equipment, security cameras for surveillance and security, and other device using Ethernet and IP can be connected at the remote site.

Modbus/TCP
Modbus/RTU is the original Modbus communication that runs on RS232 and RS485. Modbus/TCP is the successor of Modbus/RTU that runs over Ethernet media on top of a TCP/IP stack. Communication is still master-slave. The function codes and register scheme is the same. In addition to standard function codes for reading and writing I/O and memory, specific function codes permit configuration download etc. Simple bridges exist for converting Modbus/RTU to Modbus/TCP. Many users are therefore putting Modbus/TCP in the place of Modbus/RTU on an enterprise wide scale. This test was carried out using a Smar LC700 hybrid controller fitted with an ENET700 Ethernet module. Identification, configuration download, monitoring and operation from the CONF700 software and OPC server was tested successfully.

FOUNDATION Fieldbus HSE
H1 Fieldbus is used at the field-level among instrumentation. HSE Fieldbus is a sophisticated protocol at the host-level of the FOUNDATION Fieldbus system architecture. HSE runs over Ethernet media on top of a UDP/IP stack. Apart from simple process monitoring, HSE provides transparent access to field device diagnostics and configuration etc. HSE linking devices take the place of RTUs. Asset management and remote maintenance from a central location becomes possible. This open solution eradicates proprietary protocols specific to only one vendor and allows hardware to be freely selected. The protocol is rather sophisticated but the user is isolated from this complexity through the use of OPC for data integration at the host end. This test was carried out using a Smar DFI302 linking device. Identification, firmware upgrade, configuration download, monitoring and operation was tested successfully the FBTools, Syscon and OPC server.

Setup and Network Configuration
The network setup is extremely simple. The wireless Ethernet is completely transparent. The Remote device is simply connected to the Access Point. For the test a direct cable was used between device and radio, but it could just as well be a hub in between. The workstation also connects to the access point. For the test a direct cable was used, but it could just as well be a hub in between.

IP addresses were assigned to the access points using the management tool embedded in the access point running as web server, using Internet Explorer as the user interface. The access point automatically detects the remote Ethernet devices connected and displays them in an endpoint list.

Others
The MDS iNET 900 is a frequency hopping radio that requires no license. The transmission scheme is slightly different from IEEE 802.11b WiFi making it hard to detect thus preventing spying or overriding of data. Moreover, several internal settings for the frequency hopping makes it very difficult to eavesdrop or even detect the radio.

It cannot be stressed enough how much simpler using Ethernet is compared to traditional RS232 serial. With Ethernet, there is no need to configure baud rate, parity, stop bits, flow control and timeouts etc., plus all the DTE/DCE and wiring doubts. Addressing is greatly simplified too, particularly if DHCP is used. In a chain that is typically at least four devices long, eliminating these configuration requirements greatly reduce the number of things that can go wrong. There is really not much left you can do wrong.