What is scan time (or polling frequency) of OPC Server of Labview

[aithal]

What is the scantime of OPC Server.

[SamboNI]

Hi aithal,

Could you please be more specific in what you are looking for? Are you referring to the use of the LabVIEW shared variable engine as an OPC server? Or using LabVIEW to access another OPC server?

Best regards,

[aithal]

We would like to use Labview as Monitoring software of a Machine, which is controlled by Mitsubishi FX2N PLC.  The machine should run indipendently of PC where labview is installed.  We have Labview Developer suite V8.0.  We would like to capture few of the registers of PLC and graphically represent the result, and also store these values in a file. 

As a setup procedure, few of the registers of the PLC has to be modified.  But once the machine starts executing, we will only capturing the data from PLC.  We seek following clarifications:

1. For above type of work (just monitoring in real time, where about 20 words has to be captured at about 200 milli seconds, and no controlling of the PLC) is OPC server of Labview required.    If yes,  what is the minimum time interval wherein we can capture about 20 words from PLC.  One of my friend says it can not be less than 1 second, which is not acceptable.   He says to achieve scan time of less than one second require a hardware on PC side.  Is it true?

2.  If OPC server is needed should we have to purchase Drivers for Mitubishi PLC (on PC side)?

3. Is it not possible to use just Serial communication of Labview to capture info from PLC?

Thanking you.

[SamboNI]

Hi Aithal,

First of all, thank you very much for posting this additional information, as it is much more useful to help you out going forward.

To clarify, when interacting with PLCs, LabVIEW is acting as a client and the PLC (via an OPC Server) is the server. If you wished to share some data from LabVIEW to other applications via OPC, this is technically possible as well, since the LabVIEW shared variable engine acts as an OPC server.

1. I am not sure in terms of speed whether you would be able to capture this amount of data in this amount of time, as this is dependent on the device (PLC ) that you are communicating with, network traffic (if it is ethernet), etc. The data rate at which you can capture from a particular PLC with new data is going to be something you will need to determine empirically.

2. Most commonly, yes, people use an OPC server to communicate with a PLC (or sometimes Modbus). This is frequently something that is provided by their PLC manufacturer on a CD or for download, but in some instances not. We do offer Industrial Automation OPC Servers, which provides support for many common PLCs.

Once you have done this, you may either use datasocket to communicate with the OPC server, or we recommend the LabVIEW DSC Module, as it enables you to bind shared variables to your OPC items, and also adds logging, alarming and security to the variables.

3. It entirely depends upon your PLC. If it supports serial communication, then you could likely use NI-VISA commands to interface with it, and a good starting point would be the example in the Example Finder entitled "Basic Serial Write and Read.vi".

Best regards,

[aithal]

Dear Sir,

Thank you for your reply.   One of the point in my earlier mail is,  provided the PLC is very fast in communication, whether OPC server of Labview capture the data once at 200 -250 ms, or  is it limited by 1second.

Mean time, we are able to communicate with PLC in plain RS232 Serial mode, without protocol.  Mitsubishi PLC also support FX protocol.  and in OPC server page of this website it is mentioned that there is a driver for Mitsubishi PLC.  My question is if we use this mitsubishi driver from labview and use basic NI-VISA, is it possible to achieve communication through FX protocol.  Or the driver is useful only if we use OPC server?

[SamboNI]

Hi Aithal,

>whether OPC server of Labview capture the data once at 200 -250 ms, or  is it limited by 1second.

Again, I do not know what you mean by OPC server of LabVIEW. LabVIEW will be acting as an OPC client, either with datasocket or with shared variables, and the OPC server will either be the driver we provide with IA OPC Servers or one that your manufacturer provides. LabVIEW with datasocket or shared variables does not have any sort of 1 second limitation, and indeed you can loop much more quickly than that.

I am not familiar with this FX protocol. The OPC server we provide in Industrial Automation OPC Servers is an OPC server and must be accessed with an OPC client as detailed above. Your alternative appears to be to use VISA functions for the serial communication, and look up with the manufacturer what syntax it is expecting with this FX Protocol.

Best of luck, and let me know if you have further questions for me.

[Ben]

Let me jump in here for a minute.

The actual OPC server that you use to talk to your PLC is not dicated by LabVIEW.

Once you choise one there is generally a configuration page "somewhere" that lets you define the update interval.

If your network connection can handle it and you are not talking about an I/O count that staggers the mind, you should be able to achieve the update rates you are asking for.

Re: the serial protocol

That is dependent on your OPC server. For the most part, serial will often be slower than ethernet based connections.

So....

all of your questions should be posed to the supplier of the OPC server.

Adding....

If the OPC server supports data sockets, we have seen very good results by using the dynamic value change events available with DSC.

I hope that helps,

Ben

[aithal]

Dear sir,

Thank you for your answer.   I got it now.  Labview acts as OPC client and the driver provided along with IA OPC server will act as OPC Server.  (Of course, we are not going to use OPC server provided by PLC manufacturer).    It is also clear that Mitsubishi PLC Driver provided will work only if IA OPC server is installed. and there is no timing limitation as such.

K.S.Aithal