Smart device management

We know that many serial devices such as PLCs can be connected to a management or enterprise system using an OPC server. But what about communicating with serial devices using Simple Network Management Protocol (SNMP) over the internet? The answer is Smart Device Servers (SDS).

Devices are everywhere and are central to any application. Historically they were very basic and performed one task well but today they are flexible and intelligent so they can adapt to specific environments. They still have to be configured, monitored, diagnosed and maintained so device suppliers provide proprietary software tools together with connectivity to several types of fieldbus. Access to information held within devices is neither fast nor intuitive and this slows down decision-making in a highly competitive environment. End users would prefer to be able to get at all their information using a standard web browser and to have their control systems and enterprise applications as easy to use as the internet. However, the IT environment does not have direct access to devices and so users have to communicate with real-time control systems.

To achieve this, automation is moving fast into the IT domain, using 'open' standards based on Ethernet alongside standard infrastructure, protocols and tools. More control systems are being specified with management interfaces that use SNMP so that device control will be carried out at the IT level rather than the control level. Two types of management interface have now emerged: in materials handling, process lines and OEM machines, OPC and DCOM are dominant; in building management and retail the preference is for SNMP over an IP. In both cases the interfaces rely on Ethernet and use built-in operating system functionality. They also rely on a management software tool, OPC server or SNMP Manager. The most popular SNMP management software is HP Openview and IBM Trivoli, both of which are very powerful but also expensive. So suppliers are starting to put SNMP functions into their own products and these Smart Device Servers (SDS) are designed to deliver SNMP services to the IT community.

An SDS is an embedded PC located at the device to convert serial data into Ethernet packets. Physically an SDS is an interface adapter connected to Ethernet on one side and to a set of devices on the other side through a serial link, a fieldbus or, if necessary, a telephone line. It operates as a bridge between proprietary device data and an open environment so that standard IT tools can communicate directly with devices in the field.

The SDS generates alarms from temperature information read directly from the device and can also calculate the time of operation and raise maintenance alerts when thresholds have been reached. But connecting a device to Ethernet means it can be controlled remotely and there are dedicated web pages provided so it can be managed. Custom calculation or processing can be added so that raw data from the device is converted into more complex information when this is required by an IT application, something which real-time controllers would not normally be able to do. Finally, the SDS can emulate connection of the device to an SNMP Manager and will automatically generate traps when alarms occur, just as if the device was directly connected to Ethernet.

Smart Device Servers form an important bridge between the real-time control systems and conventional IT applications. They add value to legacy devices and Ethernet architectures by providing end users with better access using standard tools, which improves efficiency. The source of information is still on the plant floor embedded in devices. Some services will require custom development: of HTML pages or Script applications, but IAONA and IDA are developing standards to simplify this. With a clear definition of device profiles, which includes details of configuration, diagnosis, maintenance and management, the SDS will be able to automatically generate HTML pages or SNMP emulation so device control over Ethernet becomes more readily available.

Terry Price can be contacted on +44 (0)1892 785755 or at terryprice@lineone.net