I started a OPC UA project using the Milo project to create a OPC UA Client. I am still very new to OPC UA. Right now I am stuck looking for the best practice to read values from several Nodes after a data change of one specific node.
The information model looks like this:
RfidSensorType
On my server i will have several objects of this RfidSensorType. The client creates a subscription on the CurrentAtTag Node to listen for data changes.
My Question:
When the value of CurrentAtTag is changed a callback function will be called in my client which contains the UaMonitoredItem and the DataValue of the CurrentAtTag.
In my application i need to process (at the same time) also the values of Station, IOLPort and CurrentValue which are changed at that moment too.
How can i access those values within the callback from CurrentAtTag?
My only solution is: Using a synchronous read request within that callback
-> Is that an legit approach?
My Research:
1) TriggeringService
I've seen that a TriggerigService exists, which monitors items will send reports only if one specific node changes it values.
Problem: This will call several callsbacks and noz just one..i need all the informations at the same time to further process them..
2) Event Monitoring
In event monitoring one can select "Event fields" which will be returned for each Event notificaiton. I am not sure if i could select the CurrentAtTag, Station, IOLPort and CurrentValue...
Just like you can subscribe to the server's ServerStatus (nodeid "i=2256"), you should be able to subscribe to the nodeid corresponding to 'RfidSensor_Station1'. The server will send PublishResponse with data of type 'RfidSensorType' encoded as an ExtensionObject. The trick is decoding the ExtensionObject.
As Kevin corrected, because 'RfidSensor_Station1' is not node class 'Variable' then it doesn't have a value attribute and you can not monitor the node for data changes. If you are using a PLC, I might combine all properties of the sensor into a string, or byte array. Then I monitor the new variable, and parse the string in the client.
Or you could make ReadRequest as you describe. That will work just fine.
Related
I have a task that is create an opc server and instantaneously read data from an injection molding cnc machine with opc client. I have read a lot of documentation and came to a conclusion which I need a model information xml file and create c# classes with a compiler according to the model information file.
I have come across with OPCFoundation/UA-Nodeset repository which has Node Id's that plastic rubber devices shares.(I assume that) There is also a Opc.Ua.PlasticsRubber.IMM2MES.NodeSet2.xml file which is the final ingredient that model compiler produces.
Also I assume when I point my opc server address to the molding cnc device, I will read or machine push data with those spesific nodeIds.(I might be awfully wrong here)
Now the confusion begins here; In the Opc.Ua.PlasticsRubber.IMM2MES.NodeSet2.xml, there are some nodeIds presented. Is the data presented by the molding device published with that nodeIds or those id's are just a unique key for model file? Also when I try to create model information file, nodeId's are different. Is nodeIds should match with the nodeset2.xml?
In the end, I want to read lets say machine status data which nodeId is 5006, should match the model information file which I created in order to get data?
Thank you.
The nodeset in the Companion Specification usually contains only Types (such as ObjectTypes, VariableTypes, etc.) and sometimes an object that serves as an entry point (e.g. DeviceSet of DI). To use these types, you need to create an instance of an object in the address space of your OPC UA server. For example, in your case, the instance might be of the IMM_MES_InterfaceType. The nodes of your instance will have different nodeIds than the types.
As an OPC UA client, you should use the BrowsePath (and the browse service) to locate the correct node in the address space. Once you have the nodeId, you can read or write data from it. In the first step, you can use a generic OPC UA client such as UaExpert for browsing, but it is recommended to implement browsing in your own application. This will allow you to connect to other machines with the same interface.
In think your BrowsePath for the MachineStatus should something like this:
Objects.DeviceSet.IMM_<Manufacturer>_<SerialNumber>.MachineStatus
An example of an plastic rubber devices should be here
there is a OPC UA service TranslateBrowsePathsToNodeIds.
How volatile or stable are the NodeIDs results returned by the service ---
Is it possible that NodeIDs resolved by the service alter while server runtime?
In our Case we are running our client against a server, which enumerates NodeIDs differently on every server restart. So we decide to resolve IDs by BrowsePath once after each (re)connect to the server. So far so good. But now there is a Problem when the server is restartet and after the first client reconnect no paths can't resolved.. it seems the server is not ready for the job (...).
I am wondering how often I have to update the resolved Node IDs (all or just the onces which was not resolved correctly?).
We are reading data by polling in this case.
I don't know your server, but it seems, you do address an OPC UA Server with a very dynamic behaviour, But I think, it's within the OPC UA spec.
It depends on the OPC UA objects, this server offers and what a client should or wants do with them.
Is it possible that NodeIDs resolved by the service alter while server runtime?
Yes!
Many servers do offer a static node set from the device configuration. In this case, the client will always get the same node ids from TranslateBrowsePathsToNodeIds, the client may use the node ids directly without translation (but has always to resolve the namespace index after connecting to the server). But obviously it's not your kind of server.
Another use case are dynamic objects, with a restricted lifetime, coming and going on any time they want to come an go. Imagine a warehouse in which goods are received and delivered. So a good will be representent with an individual OPC UA object instance, created on receive and removed on delivery. As long the good exists in the warehouse, you may browse to the object, translate its browse pathes to node ids and use them (reading, writing, monitoring). Of course, when the good delivers, the UA object will no longer be needed and could be removed by the server. The node ids removed now could be used later in an other context for another object instance.
Alternatively, the server could offer an interface to create or remove objects with a client.
The question is, how the server deals with the creation or removal of it's objects, how does it announce the changes? There should be a kind of configuration change event you want to monitor with your client. When your client receives an event, it may decide which actions to do, e.g. rebrowse the object and translate the browse pathes. Read the manual!
By the way: TranslateBrowsPathsToNodeIds is widly used to adress subnodes of object instances with a known object type. Once you know the node id for the entire object, you easily get the node ids for the subnodes with their browse pathes.
I want to retrieve data per Publishing Interval, even data changed or not. As I read OPC documentation, I can only get DateChangeFilter to retrieve the values on OnChange.
Is there any way to do that?
If creating your item with a DataChangeTrigger of StatusValueTimestamp doesn't get you all the changes you want there is nothing you can do.
Alternatives would be periodically calling the Read service instead of using a MonitoredItem or maybe calling the ResendData method every time you want to force the subscription to send the last value for all its items.
I am new to opcua. I have a simple python3 client that I want to use to monitor a few voltages and currents from the opcua server.
I can subscribe to them and when they change, I can see the changed value but I don't know what the value is for.
I am trying to figure out how to use the info I know I can get like the node.nodeid.Identifier and use that to somehow get the path which is associated with the the id. That should tell me what the value is(?)
I thought it might be in the browse_name but that got me nowhere.
Any push in the right direction would be greatly appreciated. Thanks!
When your OPC UA Client want to get notified of the value update of a Node, it actually subscribe to the Attribute Value of this Node. You could try to subscribe to the Attribute BrowseName or DisplayName of the Node to get notified for the name.
You should then send a CreateMonitoredItems and set the corresponding AttributeId for each iTemToMonitor.
However, not every OPC UA Server support this feature.
Most OPC UA Client use the Browse and Read Services just before sending a CreateSubscription/CreateMonitoredItems in order to get the BrowseName/DisplayName or other attributes values they want.
I want to send data generated by my application to OPC UA client using OPC UA Server. I have gone through Eclipse Milo Project which is great resource for the same. But I don't know how to integrate it in our Application.The Application produces output in JSON format. The data of multiple nodes is stored, processed and sent using JSON format like following.
{"deviceId":"36860","timestamp":"2019-03-07 10:37:20+05:30","1":"228.6","2":"237.65","3":"237.21","4":"0.13","5":"0.0","6":"0.11","7":"-2.95","8":"0.0","9":"4.03","10":"22.2","11":"0.0","12":"16.43","13":"-21.83","14":"0.0","15":"-15.72","16":"-0.13","17":"1.0","18":"0.25","19":"262.35","20":"0.0","21":"284.18","22":"234.49","23":"703.47","24":"0.08","25":"0.24","26":"0.36","27":"1.08","28":"12.87","29":"38.62","30":"-12.52"}
where 36860 is the nodeId/deviceId, timestamp is the time when data is captured from the node rest are the Parameter Ids and their actual reading values of node in key value pair.
How to use the ExampleServer to send this data and How client would receive it ?
If possible can anyone provide an example ?
I think the first think you should decide is how to model the data in the server.
You could of course stuff that String into a single VariableNode with DataType of String but then why bother using OPC UA?