Read data from an acquisition unit at 1hz using modbus TCP

[adri73]

Hello everyone,

I am familiar with Labview but quite a beginner with numerical communication.

I will try to summurise my problem.

I use Labview 2018. I want to read the data from an acquisition unit with 7 sensors plug inside.

My program is not perfect but at this stage I succeed to read the 7 sensor with a frequency of 0.5HZ.

So all the  parameters seems OK.

When I try to read only two sensors, it reaches 1 HZ.

My last try are about structures, firstly I wanted to read my table with a structure "for" but I try to remove this structure to understand better and to see what's happening ?

I join to my post 3 VI and sub-VI and file result.

Is it possible to reach an acquisition at 1 hz or is the PC to slow to manage 7 sensor at 1 HZ?

Thank you very much,

I stay free for any further information.

[GerdW]

Hi adri,

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@adri73 wrote:

Is it possible to reach an acquisition at 1 hz or is the PC to slow to manage 7 sensor at 1 HZ?

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It's not your PC that limits the execution speed, it's the way you created your VI!

I see two major issues ("numeric_7sensors"):

1. reading 7 values in parallel over the modbus: you have a shared resource, so you need to read sequentially!!!
2. reading those 7 values by using the "read single register" calls: as those modbus values are in a range of 0x04 to 0x31 you could read them in just one call by using "read multiple registers"!

Other issues:

• Cleanup the block diagram to make the code more readable!
• You can resize the IndexArray function, so you need only one node instead of 7!
• IndexArray starts to index at element 0, so you don't need to wire any index constants!
• There's no error handling for the file saving functions!
• …

"numeric-7sensors-structureFOR" is even worse as you placed the 1s wait inside the FOR loop…

[adri73]

Hello GerdW,

Thanks a lot for your quick answer. I am sorry for my code, I try to use all of your tips but I still don't manage the frequency. For now, with the last code I try to read using sequence structure, it does'nt work either, still at 0.5HZ. Your second idea was to replace "read holding register.vi" by "read multiple register.vi" but I couldn't find "read multiple register.vi" there is always the "write and read multiple register.vi", Does this VI exist ?

I think the answer is to use only one modbus tools to read the 7 address, which one i need to use.

Thanks again,

Adri

PS  : I am sorry for my code I amnot an Labview architect

[GerdW · Accepted solution]

Hi adri,

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@adri73 wrote:

I still don't manage the frequency. For now, with the last code I try to read using sequence structure, it does'nt work either, still at 0.5HZ. 

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Did I mention "sequence frames" anywhere in my message?

Why do you think using several sequence frames will make your code run faster???

As before: you can read several Modubus registers with just one Read funciton call! That's the way to speed up communication!

I don't have that Modbus library installed on my (current) computer, so you need to read the help for eaxch Modbus function on your own…

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@adri73 wrote:

I am sorry for my code I amnot an Labview architect

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Me neither…

[cordm · Accepted solution]

You need to replace read-register(sous-VI).vi with one of these and read multiple registers at once:

Then, convert your data and keep the stuff that you are interested in, ending up with something like this:

reading multiple modbus registers and converting to float

[adri73]

Thanks a lot for your help and your time.

I will try as you say.

Regards,

Adrien Bonnefoy