Node-RED Client Instructions

Nodes

OpcUa-Item Node

An Item node represents an object inside the information model. It is used to query the server for the object that is defined with in the item field.

Properties#fig:item-node[1.1]:

The Item field: Used to define which object/node from the Information Model on the Server we are querying. It can be set in two ways:
- ns=int;s=string - where ns is the namespace in which the object resides and s is the name of the object in the information model.
- ns=int;i=int - where i is the index of the object (the index of the information model node) in the information model.
The Type field: Used to define the type of the object we are querying.
The Value field: Can be left blank, as it is only used when creating an OPC-UA Server.
The Name field: Used to set a custom name.
- NOTE: the name that we set in the Name field will be part of the msg object that is used on Node-RED. It it set in msg.browseName field. This can be useful when filtering for a specific msg that carries the value of the item we are looking for.

OpcUa-Client Node

A Client node is used to connect to a OPC-UA Server. Client nodes work in tandem with Item nodes. Normally, an Item Node is connected to a Client node, and afterward, the Client node preforms an action with the node.

Properties#fig:client-node[1.3]:

The Endpoint field: Used to configure an connection to an endpoint that is used in the Client Node. This can be done by pressing the pen icon.
- Properties#fig:endpoint[1.2]:
  - The Endpoint field: The URL of the server in the format opc.tcp://<IP>:<PORT>.
  - Other fields: Can be left at their default values.
The Action field: Used to define what action the client node will be performing.
Other fields can be left at their default state.

NOTE: Every Client Node creates its own connection to the OPC-UA Server, this can potentially consume a significant number of connections. To avoid this, group the Item nodes that are used in for the same action and connect them to a single Client node that preforms that action.

Tomorro [fig:client-node]

OpcUa-Browser Node

The Browser node is used to query the information model, just like the Client Node. It requires the Inject Node to run and is used for browsing the information model.

Properties#fig:browse-node[1.4]:

Endpoint field : Same as Endpoint field in the Client node.
Topic field : If left empty, it queries the top root nodes in the information model. Otherwise, it can be set in the same way as the Topic field in the Item node.
Name field : This is an optional field for naming the node.

It is normally chained with a Inject node to run it and a Debug node to read the output (this can be done by opening the debug tab on the right of the Node-RED page)#fig:browse-link[1.5]. It outputs an array of JSON objects.

MQTT-out Node

The MQTT out node is used to publish to an MQTT broker.

Properties#fig:mqtt-node[1.7]:

The Server field: Used to set up the MQTT broker.
- Properties#fig:mqtt-broker[1.6]:
  - The Name field: Provides a custom name for the node.
  - The Server field: Configures the IP and Port of the broker.
  - Other nodes can be left at their default values.
The Topic field: Used to specify the MQTT Topic to which the information is published.
The Name field: Provides a custom name for the node.
Other fields can be left at their default values.

Dashboard Nodes

Dashboard nodes are used to visualize the information received from the server. After setting up the dashboard, you can access the dashboard UI at <NODE-RED URL>/ui.

There are various types of dashboard nodes, including text and value nodes, as well as nodes for charts and gauges. For more information on the types of nodes available and how to use them, you can visit HERE or refer to the manual/help that is included as part of Node-RED..

Example of Setting Up a Client Configuration

This step-by-step example will explain how to configure a Node-RED client-side for an OPC-UA Server. The information model for this example contains two objects: the TempSensor and LightSensor.

Both objects contain four variables :

SensorID - ID of the sensor.
VendorID - ID of the vendor of the sensor.
CurrentTemp or CurrentLight - Current temperature or Current light intensity.
Active - Is the sensor active and operating.

The end goal is to create a Node-RED Client side, that reads the active status and CurrentTemp/CurrentLight from the respective sensors.

Step 1: Reading From The Server

Setting Up The Inject Node

First, we need an Inject Node, which is a basic node that is part of Node-RED and can be found under the common tab.

Most of the Inject node’s properties can be left at their default values. Optionally it can be named and the two fields that are generated by default can be removed. What needs to be set-up is the Repeat field., which should be configured to interval from the dropdown list and set to 0.1 seconds#fig:inject-node[2.1].

Setting Up The Item Node

The second step is to create Item nodes for the variables we want to query. Since we want to track the status and readings from the sensors, we will need four Item nodes: two nodes for the temperature sensor and two nodes for the light sensor.

The temperature sensor is in namespace 2 and the light sensor is in namespace 3. The first Item node will be for the current temperature#fig:currenttemp-node[2.2].

Item field: The CurrentTemp variable is in namespace 2 and has an index of 6011, so we set it to ns=2;i=6011.
Type field: CurrentTemp is of type Double.
Value field: This field does not need to be set up since it is only used when creating a Node-RED OPC-UA server.
Name field: The name can be set to anything, it will be set to CurrentTemp for clarity and future ease of use in other nodes.

This is repeated for the other three values we want to track.

Afterwards, we connect all four Item nodes to the Inject node#fig:inject-item[2.3].

Setting Up The Client Node

The third step is to connect the Item nodes to the Server node. Since all four Item nodes will be used to track the values of the four variables, we only need a single Client node#fig:client-node-properties[2.4].

Endpoint field: We set it to one of the IP:PORT URLs on which the server listens.
Action field: We decide to go with SUBSCRIBE, we could as well go with READ.
Interval field: We set it to 10 milliseconds.
Other fields are optional.

NOTE: In place of the IP, you can and should use a DNS name. In the Sandbox environment use base-opc-ua-server.

Now we connect the four Item nodes to the Client node. All four are connected to the same client node, so we save up the number of connections to the server#fig:item-client[2.5].

Step 2: Sending The Data Through MQTT

Setting Up The Function Node

This is an optional step. The Function Node is used to transform the ’msg’ object sent by the Client node. The MQTT node sends out the ’msg.payload’ field of the ’msg’ object. This means that it only sends the value it just read but doesn’t indicate which Item node this value is connected to. To address this, we will take the ’msg’ object and create a new one, where ’msg.payload’ contains four fields: timeStamp, topic (which corresponds to the item field in the Item Nodes), browseName and payload as seen in #fig:function-node[2.6].

Setting Up The MQTT Out Node

First, we need to set up the Server field. To do this, click the pen icon located to the right of the field#fig:mqtt-merge[2.7]. This action opens a tab for configuring the broker.

Setting up the broker:

Server field: Here, we enter the IP and PORT of the MQTT broker.
Other fields can be left at their default values.

Afterward, we configure the Topic field, to the topic which we wish to publish on. Other fields can be left at their default settings.

image::step2-mqtt.png[Left side: Properties of the MQTT Broker. Right side: Properties of the MQTT Out node]

Now we connect the Client node to the Function node and the Function node to the MQTT out node#fig:client-func-mqtt[2.8].

Client to Function to MQTT node connection

Step 3: Creating The Dashboard UI

Setting Up The Text Node

The Text node is used to visualize data on the UI. It will be displayed in the format TEXT VALUE. This will be used to display the respective sensor status. For the temperature sensor, create the node and set the value of the Label field to Temp Active.

Since all values from all item nodes will flow down this connection, we need to filter out the ActiveTemp item. To do this, we use the msg.browseName and the Fork node#fig:switch-text[2.9].

Switch node on the right and Text node on the left

We do the same for the ActiveLight value.

Setting Up The Chart Node

We use the same switch node for filtering out CurrentTemp and CurrentLight values, but this time connect them to Chart nodes. Also add a Text node for both values, to display the current values.

In the properties of the Chart node, we only set up the Label field.

We also add a Delay node, to delay the UI update times, if we wish to use it. The delay can just be set to zero or removed.

Finally, we connect all the switch nodes to the Client node and the switch nodes to the Dashboard nodes #fig:fin[2.10].

Deploying And The UI

By clicking the Deploy button located in the top right corner, it connects to the OPC-UA Server and the MQTT Broker, and starts reading data.

You can access the user interface (UI) at`<Node-RED IP>/ui`#fig:ui[2.11].

Afterwards use the client.py script to simulate posting data to the server and displaying it on the UI.

Example Of Writing To The Server

To write back to the server, we set the Client node Action field to write and connect the Item node to the Client. To send the payload, we add an Inject node and set the field to msg.payload and the value we want to write#fig:write[2.12].