Receiving empty values from KepServer (as an alternative to a TOP server)

[Seong]

Hi there,

I am experimenting an opc example with Kepware from the help of the utgard website: "https://openscada.atlassian.net/wiki/display/OP/HowToStartWithUtgard"

The following code is part of my example:

// connect to server

server.connect();

// add sync access, poll every 500 ms

final AccessBase access = new SyncAccess(server, 500);

access.addItem(itemId, new DataCallback() {

@Override

public void changed(Item item, ItemState state) {

System.out.println(state);

}

});

// start reading

access.bind();

// wait a little bit

Thread.sleep(10 * 1000);

// stop reading

access.unbind();

The program connects and runs successfully

There are times where I actually receive values of boolean tags that are either true or false (1 or 0) but this is rare.

However I mainly receive the following line:

Value: [[org.jinterop.dcom.core.VariantBody$EMPTY@d60b970]], Timestamp: Wed Feb 18 22:58:23 GMT 2015, Quality: 0, ErrorCode: 00000000

is there an explanation why I receive this?

Nevertheless, my main question is the following.

The example is focused on getting values of a same tag over a certain period of time.

Is there any way to get data without specifying a time period?

Thanks in advance.

Kind regards

Seong 

[Jens Reimann]

Hi,

well "EMPTY" is a valid return value for OPC. So the question is why your server provides this value?! But I cannot answer this for you, sorry.

What do you mean by "time period"?

Best regards

Jens

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[Seong]

Hi Jens,

I am so sorry. I apologise. I saw your message yesterday night.

Thank you. The server sometimes returns an empty value. I don't know why. I think it's Kep server(program) problem.

What I meant by 'time period' was,

final AccessBase access = new SyncAccess(server, 500);

&

Thread.sleep(10 * 1000);

both 500ms and 10000ms. I interpret it as it tries to get a value over 10000ms every 500ms.

What a program I wrote does, it prolongs a server connection until it gets a value from the server.

I am looking for a method that retrieves a value without asking a user to specify a time period.

Is there such method? The program I wrote using your code does the job. However I think your method is certainly going to be much more robust and fast.

Thank you for your valuable comment.

Kind regards

Seong

[Jens Reimann]

Hi,

Well if you need only a one time read you can use the low level api. Just look into the source of SyncAccess.

Jens

[Seong]

Hi Jens,

Thank you for your valuable and previous comment. I really appreciate your kindness.

I have looked at the source code. I have decided to stick to the previous way (your high-level method).

I think runOnce() method may not get the right value at once because Kep server seems not fully compatible to Open Scada and it doesn't return the right value at once. I have to iterate until it does so.

Getting a value for each item(tag) takes around 20ms - 100ms. There seems many items that needs to be queried. I think there are more than 1,000,000 items. Can you suggest me a quicker way or appropriate values for SyncAccess and thread.sleep please?

or do you have a method that checks values for a group of items and returns changed values?

like

Group group = server.addGroup ( "test" );
group.addItem ( "Saw-toothed Waves.Int2" );

group.addItems( "Saw-toothed Waves.Int2", "Saw-toothed Waves.Int4" );

Nevertheless, I don't know how to get item values from group object. Because

access.addItem(itemId, new DataCallback() {
    @Override
    public void changed(Item item, ItemState state) {

        // System.out.println(state);  // System.out.println(item);

is for one item.

or I just have to ask you for a quicker way to get values for many items.

Thank you.

Kind regards

Seong

[Psyco Tik]

state.getValue() inside the changed method returns a JIVariant type. From there you can use;

switch (input.getObject().getClass().getSimpleName()) {

case "JIUnsignedShort":

output = input.getObjectAsUnsigned().getValue().shortValue();

break;

case "JIUnsignedInteger":

output = input.getObjectAsUnsigned().getValue().intValue();

break;

case "Integer":

output = input.getObjectAsInt();

break;

case "Short":

output = input.getObjectAsShort();

break;

case "Boolean":

output = input.getObjectAsBoolean();

break;

case "Float":

output = input.getObjectAsFloat();

break;

default:

output = input.getObject().getClass().getSimpleName();

break;

where input is state.getValue().

Is this what you are looking for?

[Seong]

Hi,

 

I much appreciate your instructions however they seemed focused on how to get a value one by one from a set which is already queried from PLC.

 

Nevertheless , I would like to know how to put items in a group and to then retrieve values of those items in the group through a single query.

 

I looked at examples (Tests.java files) but just could not figure it out.

 

Thanks in advance

 

Kind regards

 

Seong