Delay in rs 232 visa

[Sarichal]

While communicating with a Siemens PLC in point to point protocol RS-232 using VISA commands, I encounter to some undesired delays which restrict timeout reduction.

The same action could be taken place by Implementing the same communication algorithm on the same protocol, executed by micro controllers. Here this time-out restriction does not reveal. Does any one has an idea to resolve this problem?

[Dennis_Knutson]

How much is this delay? What programming language? Can you attach your code?

[Sarichal]

Hello Dennis,

Thanks for your attention. the occured delay is 30 msec between each VISA write command. I attached the related simple block diagram.

I am awaiting...

[Albert.Geven]

What happens when you build all outputs in one string and output this, instead of calling visa for each character?

[Sarichal]

Hello.

I did it before. Unfortunately nothing happened!

[Albert.Geven]

no delay or no action in the plc?

[Sarichal]

Yes. Nothing as particular. When I recalled a command, I could see by my eyes the delays between running the command and recalling it!

Is that required to use authorize RS232 PCI cards of NI? You see, while working with NI IMAQ USB instead of PCI 1411, you encounter to a reduction in frame acquisition. It reduced to almost 15. I think this is a kind of intentional restriction to encourage users to buy expensive cards! Is'nt it?

[Sarichal]

Yes. Nothing as particular. When I recall a command, I can see by my eye the delay between recalling and running the command.

Do you think that it relates to the use of authorized NI PCI RS 232 cards? You see, for example, when using NI IMAQ USB instead of NI PCI 1411, you encounter to a reduction in frame rate, it reduces from 25 to 15, and it does not matter what is the CPU usage. It is deliberately indeed!

However, I guess this problem relate to the same reason! Isn't it?

[Albert.Geven]

Or maybe your USB camera is slower....

I really don't understand what does and what does not happen. Sorry for not understanding.

[Dennis_Knutson]

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@Sarichal wrote:

Yes. Nothing as particular. When I recall a command, I can see by my eye the delay between recalling and running the command.

Do you think that it relates to the use of authorized NI PCI RS 232 cards? You see, for example, when using NI IMAQ USB instead of NI PCI 1411, you encounter to a reduction in frame rate, it reduces from 25 to 15, and it does not matter what is the CPU usage. It is deliberately indeed!

However, I guess this problem relate to the same reason! Isn't it?

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I think it is ridiculous to think that NI would reduce the VISA speed when using non-NI hardware. Are you using a USB-RS232 adapter? There is considerable latency with that type of connection. How are you measuring the delay? I would also agree that you should send the entire string at once.