Explaining the Modbus Scanner - Health Scan Rate

The Modbus Scanner in Remote Connect is meant to simplify Modbus polling so that it does not have to be managed via logic. If a user finds the scanners too restrictive for their desired polling scheme, the MB_SERIAL_MASTER and MB_IP_MASTER function blocks can be used in logic and triggered as needed.

With RemoteConnect 3.5.3 and corresponding firmware 9.13.3, Health Scan Rate was added to the Modbus Server Device setup.  When the SCADAPack detects that a remote device has gone offline, the Health Scan Rate determines how long the controller will wait before attempting to communicate again to this device.

For the configuration above, the Modbus scanner is set to poll the remote device every 500 ms. If communications fail to this remote device (remote device powered off, problem with the communication path, etc...) , the Modbus Scanner will wait the Timeout period (1000ms) before re-sending the message.  The Modbus scanner will continue to timeout and retry until the Maximum Consecutive Timeout (3) is reached. At this point, the Remote Device status will become Offline and the Modbus Scanner will go about and continue polling other devices.

Once the Health Scan Rate period is reached (15000ms), the Modbus scanner will attempt once more to reconnect with this particular device. If it times out, the scanner will continue to use the Health Scan Rate to determine how often it will attempt to re-establish communications to this device. As soon as a poll to the Offline device is successfully completed, the status will be updated and the scanner will revert back to the default scan rate (500ms).

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