Some tests when learning OPC UA

Tools

Python libs: pip install opcua paho-mqtt

Prosys OPC UA simulation server: https://downloads.prosysopc.com/opc-ua-simulation-server-downloads.php

mosquitto (the MQTT broker): https://github.com/eclipse/mosquitto

Tests

Test 1. Hello world: with an online OPC UA server

Run helloworld_milo.py to connect with milo OPC UA server

Test 2. Hello world: with a local OPC UA server (Prosys)

1. Run Prosys OPC UA simulation server
2. Run helloworld_prosys.py

Test 3. Read data: with a local OPC UA server (Python)

1. Run server_test.py
2. Run client_test.py

This is to retrieve data by calling get_value() periodically. The followings are to retrieve data using Sub/Pub mode.

Test 4. Sub/Pub: over opc.tcp

1. Run server_test.py
2. Run client_subpub_opctcp.py

ChatGPT: The opcua library primarily supports the client-server model over TCP, so for Pub/Sub over UDP, additional steps and potentially different libraries are needed. Using OPC UA Pub/Sub over UDP in Python requires either specific support in your chosen library or the use of a C library like Open62541 with appropriate bindings.

class SubHandler() is from python lib opcua, for Sub/Pub over TCP.

Test 5. Sub/Pub: over MQTT, using mosquitto_pub and mosquitto_sub

1. Run in shell: mosquitto
2. Run in shell: mosquitto_sub -t "test/topic" -v
3. Run in shell: mosquitto_pub -t "test/topic" -m "hello world"

See: eclipse/mosquitto: Eclipse Mosquitto - An open source MQTT broker (github.com). It is better to use " instead of ', as it seems they can make differences.

Test 6. Sub/Pub: over MQTT, using paho.mqtt and mosquitto_sub

1. Run in shell: mosquitto
2. Run publisher.py
3. Run in shell:

mosquitto_sub -t "sensor/data" -v

In this test, paho.mqtt.client.publish() as publisher, mosquitto_sub as subscriber.

Test 7. Sub/Pub: over MQTT, using paho.mqtt

1. Run in shell: mosquitto
2. Run publisher.py
3. Run subscriber.py In this test, paho.mqtt.client.publish() is used as publisher, subscribe() as subscriber.

Test 8. Sub/Pub: over MQTT, using Prosys simulation server

1. Run in shell: mosquitto
2. Run Prosys simulation server, and set up in the PubSub tab,
   1. Key settings include address, encoding.
   2. The queue name is the topic name.
   3. Test it with mosquitto_sub -t "prosysopc/json/data/urn:BGO-1043.ad.norceresearch.no:OPCUA:SimulationServer/WriterGroup1/VariableDataSetWriter" -v
3. Run subscriber.py

In this test, Prosys simulation server is used as publisher, subscribe() as subscriber.