Yokogawa Standalone MW100 - Manual (Page 45)

7 - Device Communication Watchdog Example
7.0 DX Advanced / SLC 5/05 Watchdog Example
For any control application, communications validity is a key factor, especially when utilizing I/O devices. If the PLC is
utilizing a DX Advanced for analog input data with which the process will use for output determinations, it is critical that
should communication between the PLC and DX Advanced be lost, the situation be detected and the appropriate actions
taken to insure the application’s proper steps, whether it be to shut down the process or compensate in anot her manner.
In this example, an SLC 5/05, IP address 192.168.001.010 is communicating with a DX Advanced, IP address
192.168.001.100. Using Math Channel 110 in the DX Advanced, an equation is set up to toggle the channel value
between 1 and 0 on a time interval determined by the DX Advanced Scan Interval (1 Second in this example). When
using an MW100, if a faster scan interval is being used, take steps to insure that the interval selected allows for a
complete communication cycle between the MW100 and PLC so that each Watchdog Value transition (Math Channel 110
in this example) is successfully transmitted to the PLC on each communication cycle.
The equation in Math Channel 110 is as follows:
When the channel is first scanned, it will be equal to ―0‖. Since it is not equal to Math Constant K11(1), the value will be
set to equal K11 (1). On the next scan, since the value is equal to K11 and the equal statement is true, the channel value
will be set to equal K10 (0). The channel will continue to toggle at 1-second intervals.
Below is an example of logic used to determine the SLC 5/05 and DX Advanced Communication status……
Scan Interval setting in DX Advanced “Basic Setting” area
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