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Wolfgang Hottgenroth
2022-02-22 17:15:33 +01:00
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# OPC-UA to MQTT Bridge
## Installation
* Take the tarball from the Release area and unpack it in the desired location on the edge device
* The systemctl service script assumes to find the application at `/home/alarm/KROHNE/opcua2mqtt-bridge`, so it is a good idea to put it there
* Create a configuration directory `/etc/opcua2mqtt-bridge` and place the adjusted `config.json` into it
* Enable the service using `sudo systemctl enable /home/alarm/KROHNE/opcua2mqtt-bridge/opcua2mqtt-bridge.service`
* Start the service using `sudo systemctl start opcua2mqtt-bridge`
* Check the log messages using `journalctl -f`
## Configuration
``
{
"mqtt": {
"broker": "172.16.2.16",
"port": 1883,
"publishTopicPrefix": "opcua"
},
"stats": {
"topic": "statistics",
"period": 60
},
"opcua": [
{
"enabled": "true",
"type": "flat",
"url": "opc.tcp://172.16.3.60:4840",
"name": "apl",
"period": 1.0,
"timeout": 1.0,
"nodes": [
{ "ns": 0, "n": "i=345", "d": "pv" },
{ "ns": 0, "n": "i=348", "d": "sv" },
{ "ns": 0, "n": "i=351", "d": "tv" },
{ "ns": 0, "n": "i=354", "d": "qv" }
]
}
]
}
``
The configuration object consists of three parts: `mqtt`, `stats` and `opcua`.
In `mqtt` the access to the broker is configuration and the prefix for the topics used by the statistics module and the actual bridge are defined.
Besides the above shown attributes the `login` and `password` for authentication at the broker and `ca`, `cert` and `key` for TLS connections to the broker are available. `ca`, `cert` and `key` contain the filenames including complete path of the particular files.
In `stats` the topic suffix and the period of statistics messages are defined. The complete suffix will be `${mqtt.publicTopicPrefix}/${stats.topic}`.
The section `opcua` contains a list of OPC-UA servers to be queried. Each entry can be enabled/disabled using the attribute `enabled`. The attribute `url` obviously has the URL to connect the server, `period` is the period to repeat queries and `timeout` is the timeout when talking to a server.
`name` identifies the particular server, it becomes part of the topic of the published MQTT messages. The attribute `type` defines whether the individual variables of an OPC-UA server shall be communicated in individual MQTT messages (`flat`) or all variables of a server in a single message (`structured`).
The attribute `nodes` finally contains the list of variables to be queried. It contains the namespace index (`ns`), the node-id (`n`) and an optional descriptive name (`d`). Namespace index and node-id can be determined using for instance UAExpert when browsing the server and navigating to the relevant variables. The descriptive name - if given, otherwise the display name of the variable is used - becomes in `flat` mode part of the topic, in `structured` mode it becomes an attribute name within the message.
In `flat` mode the final topic will be `${mqtt.publicTopicPrefix}/${opcua.name}/${opcua.node.ns}/${opcua.node.d}`
An example for the MQTT messages according to the above configuration in `flat` mode is:
``
opcua/apl/0/pv {"serverName": "apl", "nameSpaceIndex": 0, "variableName": "pv", "value": 19.849281311035156}
opcua/apl/0/sv {"serverName": "apl", "nameSpaceIndex": 0, "variableName": "sv", "value": 1688.5152587890625}
opcua/apl/0/tv {"serverName": "apl", "nameSpaceIndex": 0, "variableName": "tv", "value": 22.574615478515625}
opcua/apl/0/qv {"serverName": "apl", "nameSpaceIndex": 0, "variableName": "qv", "value": NaN}
opcua/apl/0/pv {"serverName": "apl", "nameSpaceIndex": 0, "variableName": "pv", "value": 19.849281311035156}
opcua/apl/0/sv {"serverName": "apl", "nameSpaceIndex": 0, "variableName": "sv", "value": 1688.5152587890625}
opcua/apl/0/tv {"serverName": "apl", "nameSpaceIndex": 0, "variableName": "tv", "value": 22.574615478515625}
opcua/apl/0/qv {"serverName": "apl", "nameSpaceIndex": 0, "variableName": "qv", "value": NaN}
``
In `structured` mode the final topic will be `${mqtt.publicTopicPrefix}/${opcua.name}`
An example for the MQTT messages according to the above configuration in `flat` mode is:
``
opcua/apl {"pv": 19.844480514526367, "sv": 1689.9193115234375, "tv": 22.68524169921875, "qv": NaN}
opcua/apl {"pv": 19.844480514526367, "sv": 1689.9193115234375, "tv": 22.68524169921875, "qv": NaN}
opcua/apl {"pv": 19.844480514526367, "sv": 1689.9193115234375, "tv": 22.68524169921875, "qv": NaN}
opcua/apl {"pv": 19.844480514526367, "sv": 1689.93701171875, "tv": 22.620391845703125, "qv": NaN}
``