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LOGO 8 and modbus RTU

Created by: Avtovazov at: 4/29/2022 8:56 AM (11 Replies)

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4/29/2022 8:56 AM	Rate (0)
Avtovazov Regular Member Joined: 5/28/2018 Last visit: 3/20/2025 Posts: 29 Rating: (0)	Good afternoon. Please help me figure it out. I have a weight converter for working with load cells, it has a MODBUS RTU protocol, I also have a MODBUS RTU to MODBUS TCP converter (USR-DR302). I need the logo to receive the values of the current weight from my weight converter. I managed to set up the connection and the logo receives some data from the weighing terminal, but the logo displays this value incorrectly, it constantly changes (jumps) from -9999999 ... to 999999... and it does not display what is actually there. To check the connection, I connected the OPC-server to the weighing terminal and I get the correct data there. The only thing in the OPC-server settings, I had to choose the byte permutation option in the device so that the value was transmitted correctly. Is there the same function in LOGO, so that data is transmitted by the highest byte forward?
	Last edited by: Avtovazov at: 04/29/2022 08:59:20
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4/29/2022 9:02 AM	Rate (0)
ixo65 Grandmaster Joined: 12/18/2014 Last visit: 9/14/2025 Posts: 35958 Rating: (4501)	To do this, we would first have to know how the data is transferred to the LOGO!.

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4/29/2022 10:06 AM	Rate (0)
Avtovazov Regular Member Joined: 5/28/2018 Last visit: 3/20/2025 Posts: 29 Rating: (0)	I made a small video of what is happening, maybe it will be easier to help me this way https://disk.yandex.ru/i/fzjET3TrIUMM_w

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4/29/2022 10:15 AM	Rate (0)
ixo65 Grandmaster Joined: 12/18/2014 Last visit: 9/14/2025 Posts: 35958 Rating: (4501)	I'm sorry, but the video is not in good quality to see what you mean. And I don't speak or read Russian. The value that you transfer to the LOGO!: What is it for a data format? DInt? Float? Is it a 4 byte value? Little Endian? Big Endian?

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4/29/2022 10:40 AM	Rate (0)
Avtovazov Regular Member Joined: 5/28/2018 Last visit: 3/20/2025 Posts: 29 Rating: (0)	ixo65 I'm sorry, but the video is not in good quality to see what you mean. And I don't speak or read Russian. The value that you transfer to the LOGO!: What is it for a data format? DInt? Float? Is it a 4 byte value? Little Endian? Big Endian? Data format: Float, yes 4 bytes value. Little Endian? Big Endian? I don't understand what it means?

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4/29/2022 12:34 PM	Rate (0)
ixo65 Grandmaster Joined: 12/18/2014 Last visit: 9/14/2025 Posts: 35958 Rating: (4501)	big-endian and little-endian Can you say if you must words swap? 3412 to 1234? Or all 4 bytes swap? 4321 to 1234?

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4/29/2022 1:08 PM	Rate (0)
Avtovazov Regular Member Joined: 5/28/2018 Last visit: 3/20/2025 Posts: 29 Rating: (0)	ixo65 big-endian and little-endian Can you say if you must words swap? 3412 to 1234? Or all 4 bytes swap? 4321 to 1234? I think the first option is 3412 to 1234, but I'm not sure, in the photo below the location of the bits that work correctly in the opc-server and display exactly what is on the weighing terminal. [snip] Now I have to read the data from the weighing terminal and display it on the logo, but there is some kind of offset by several units of weight and the more I load the scales, the greater this offset becomes, although on the opc server everything shows as on the terminal screen, and there is an offset on the logo. The weighing terminal has 557 grams, and the logo displays 554 [snip] Attachment Images.zip (756 Downloads)
	Last edited by: Jen_Moderator at: 05/02/2022 07:29:47 Links removed and added files as an attachment.
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4/29/2022 1:25 PM	Rate (0)
ixo65 Grandmaster Joined: 12/18/2014 Last visit: 9/14/2025 Posts: 35958 Rating: (4501)	You read the value in the LOGO! as a float with three decimal places. The value is given as "kg.g", e.g. 15 kg 457 g = 15.487. Is that right?

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4/29/2022 1:41 PM	Rate (0)
Avtovazov Regular Member Joined: 5/28/2018 Last visit: 3/20/2025 Posts: 29 Rating: (0)	ixo65 You read the value in the LOGO! as a float with three decimal places. The value is given as "kg.g", e.g. 15 kg 457 g = 15.487. Is that right? I didn't load the scales up to 15 kg, I don't have such weights, but with a load of 3.086 kg, the logo displays it as 3078. I want to make a very accurate scale with a sample of 1 g, so it is important to me that the logo sees what is indicated on the weighing terminal gram in gram

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4/29/2022 1:45 PM	Rate (0)
ixo65 Grandmaster Joined: 12/18/2014 Last visit: 9/14/2025 Posts: 35958 Rating: (4501)	Avtovazov ixo65 You read the value in the LOGO! as a float with three decimal places. The value is given as "kg.g", e.g. 15 kg 457 g = 15.487. Is that right? I didn't load the scales up to 15 kg, I don't have such weights, but with a load of 3.086 kg, the logo displays it as 3078. I want to make a very accurate scale with a sample of 1 g, so it is important to me that the logo sees what is indicated on the weighing terminal gram in gram I think the problem is the F/I converter in the LOGO! and that the normally works only with 16 bit Integer.

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5/6/2022 7:34 AM	Rate (0)
AutoGen_380038 Silver Member Joined: 9/11/2014 Last visit: 9/12/2025 Posts: 867 Rating: (37)	Hi, try like in the picture: If your scale give the value 12.123KG = 12123 in LOGO!, then this should work with a resolution of 1g. For a display of the value you need analog amplifier to define how to display what you want. This should work till 32755 = 32.755kg 1:1. You can check in the simulation. Open the datatable to enter the values from your scale (left side in the picture) Important is that your scale give the value 1:1 als float. Then you can use the F/I-FB with a resolution of 1.000. In this case LOGO! just translate from float to Integer. The accepted range is the LOGO! integer range till 32755, which is 32.755kg. Hope this helps. Attachment a_Wight.zip (559 Downloads)

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5/6/2022 8:25 AM	Rate (0)
Avtovazov Regular Member Joined: 5/28/2018 Last visit: 3/20/2025 Posts: 29 Rating: (0)	AutoGen_380038 Hi, try like in the picture: If your scale give the value 12.123KG = 12123 in LOGO!, then this should work with a resolution of 1g. For a display of the value you need analog amplifier to define how to display what you want. This should work till 32755 = 32.755kg 1:1. You can check in the simulation. Open the datatable to enter the values from your scale (left side in the picture) Important is that your scale give the value 1:1 als float. Then you can use the F/I-FB with a resolution of 1.000. In this case LOGO! just translate from float to Integer. The accepted range is the LOGO! integer range till 32755, which is 32.755kg. Hope this helps. Unfortunately it doesn't work. Apparently, after all, there really is a problem in the conversion in the float/integer logo block itself. I get it when weighing 1000g logo displays it as 999, and when I weigh 1,235kg logo already displays it as 1231g. there is some kind of displacement and so on all ranges, if I weigh 2 kg logo displays them as 1999, and when I weigh 2,412 logo displays this as 2408g. Apparently I want too much from the logo, so that he counts everything to me up to 1g. But thanks for the answers anyway.
	Last edited by: Avtovazov at: 05/06/2022 08:26:29 Last edited by: Jen_Moderator at: 05/06/2022 08:54:00 Text edited for better reading.
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