Active OPC Server—From Pull to Push. Moxa ioLogik E1510-T

ioLogik E1500 Series Active OPC Server Utility

OPC Client/Server creates a common interface to connect to different devices

Active OPC Server—From Pull to Push

When looking up an I/O device’s Modbus table, 19 or more steps are required to create a single tag. The steps include specifying the IP address, selecting the protocols, and defining the data type. The procedure is repeated over and over until all the devices and tags are created. It takes about 1 minute for a user with a technical background to create one tag. But what if there are 400 tags in an OPC system? Not only does it take a long time to configure such a large number of tags, it also puts a heavy load on the CPU.

OPC also requires the connected I/O devices to use fixed IP addresses. This type of architecture is sometimes referred to as “pull” technology, because the OPC server always needs to pull data (by “polling”) from the I/O devices for tag creation, IP connection, and tag status updates.

Moxa’s ioLogik Active Ethernet I/O products offer I/O status reports via TCP/UDP messaging, e-mail, and SNMP traps. In addition, they now support OPC technology. An ioLogik can automatically generate tags without requesting any data or even a device’s IP address. All the user needs to do is launch the Active OPC Server program, and the I/O channels selected by the user will be “pushed” from the ioLogik to the Active OPC Server.

5-3

ioLogik E1500 Series Active OPC Server Utility

The “push” technology also includes the update for the tags. When the I/O status changes, the ioLogik will send updates to the Active OPC Server. Compared to polling the status (the so-called pull-based method), this feature efficiently reduces network bandwidth usage and speeds up response time with event-driven, push-based status updates. At the same time, the heartbeat function monitors the system’s basic signs of life.

DI 1=ON

DI 1=OFF

DI 0=ON

DI 0=OFF ioLogik Tag Update ioLogik Idle

Push for tag updates

Heartbeat every X seconds

ioLogik

Active OPC Server

Check every 5 seconds ioLogik Alive ioLogik Not Alive

Heart Beat

5 10 15 20 25 30 35 40 Time (sec)

5-4