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Stand-Alone Control

How to make it work with standard MMI software

Remote I/O hardware performs certain essential functions:

In many industrial control implementations, the remote I/O hardware does not participate in the actual control decisions-it merely passes control signals between the host and the process under control.

In some situations, the Control Engineer may elect to implement control decisions at the Remote I/O connection point. Considerations of safety, speed, or economic factors can influence this decision:

Such implementations are increasingly common as PC-based hosts displace special-purpose PLC or DCS controllers. Although a PC operating under conventional system software like Windows or Windows NT is extremely powerful, it was not designed to operate in a hard, deterministic, real-time mode. To bridge the gap, duTec Remote I/O products some useful and important features.

Local Control Functions

PID mailerAll current duTec Remote I/O products include standard firmware, called Local Control Function  (LCF) blocks. These logic blocks can connect to "real" sensors and actuators, and to one another, to perform a variety of data acquisition and control functions:

These functions can be specified, documented and installed in a duTec product using an intuitive, graphical configuration program called the LCF Program Generator. This Windows program makes it simple to program a fail-safe, responsive control scheme which can operate in parallel with a host MMI. If communications are interrupted, or if normal operation does not require host intervention, the process will continue to function, executing within the I/O controller itself.


In most implementations, Remote I/O operates in "speak when spoken to" mode-responding with a frame of data only when polled by the host device. In some cases, it may be desirable for the Remote I/O to initiate a scan based on an event, such as an alarm condition, detected in the process:

The duTec "Speak-on-Event" feature can be used to control such processes. During setup, one or more digital "events" (which may be derived from LCF Block logic) are designated to trigger a scan. When the duTec Remote I/O product detects one, it initiates a request to the host to intervene. If required, the Speak-on-Event firmware will even dial a phone modem and emit a "modem init" string to establish the connection with the host. A frame of current data can them be presented to the host software for analysis and response. The "Speak-on-Event" firmware is coupled to a DDE driver in the host, which in turn communicates with third-party MMI or SCADA software.

Dynamic Data Exchange (DDE)

Microsoft's Dynamic Data Exchange (DDE) feature allows separate programs, running simultaneously, to exchange data. The feature is part of application programs like EXCEL™, FoxPro™, and Lotus-123™. Most MMI software vendors now offer DDE-compliant modes of operation, opening up real potential for the Control Engineer. The DDE server (or driver) from duTec is the source of the data. A DDE client, such as an MMI or SCADA package, asks for and receives data from the server. More than one client can view data provided by a single DDE server.

In addition to providing a high degree of inter-operability, the duTec DDE driver responds to "Speak-on-Event" scan requests from the Remote I/O hardware.

Demonstration versions of the duTec LCF and DDE software are available for free downloading from the duTec website.

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