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Old March 10th, 2005, 01:06 AM   #1
TEOWK
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Load Cell with PLC RS485

I have a new project that applies 4 load cell to a single weighing indicator. The load is a cement powdwer buffer hopper. Total load is 30 ton including the hopper.

1) Is there any special requirement for the cable that connect these 4 load cell to Mettler Toledo Indicator, as the distance from the load cell to weighing indicator will be about 150m.

2) I am told to use a OMRON PLC. This project require a sum of four weighing indicator, each connect to 4 load cell. I planned to use an RS485 with protocol macro to obtain the weight data. Does Mettler Toledo support OMRON protocol in this case?
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Old March 10th, 2005, 03:02 AM   #2
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posibel solution for Load cell

hi, im sajjad, i have done a project like ur requirement one year ago. in that project i have used a Level Logic Translator circuitry. i have used the load cell's Exitation signals to the opamp and then fed these amplified signals to A/D. then interface these A/d prallel signels into MAXIM Inter facing system chips with some extrnal components. i do it for Weigh Bridge measurments capacity from 1 gm to 20 tons Highly presise.
i hink this solution will be ur requirement, if ur intrested in this u can contact me at this email address: jamezrojer@yahoo.com
thanks.
Kh.Sajjad Hussain
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Old March 10th, 2005, 03:30 AM   #3
TEOWK
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Thank you. I would like to know if anyone had connect OMRON PLC to Mettler Toledo load cell through RS 485 protocol? I am not sure what the protocol is? If OMRON is a protocol macro, what is needed in Weighing indicator?


Thanks.
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Old March 10th, 2005, 04:00 AM   #4
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TEOWK,
what is the baudrate going to be ?
RS485 can run very long distances, but it depends on the baudrate. I know that for Profibus (which uses RS485) it can run 1000 meters at 187.5 kBaud. If you are in doubt, use Profibus cable it is so common that it is not so expensive.
There must be terminating resistors at the ends of the cable.
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Old March 10th, 2005, 05:06 AM   #5
TEOWK
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Thank you.

In considerarion of cost factor in my country, profibus is expensive and OMRON has a better support on device net. I am not sure on the protocol for the Mettler Toledo RS485. Are they the device net or other protocol?

The project require OMRON PLC and Mettler Toledo Load cell system, I would like to know what are the suitable parts for CJ1M series OMRON PLC?
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Old March 10th, 2005, 05:35 AM   #6
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I just mean to say that if the baudrate is not so high you should have no problems with a distance of 150 meters when using RS485.

Apart from that I have no knowledge of Omron or Mettler-Toledo.
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Old March 10th, 2005, 06:31 AM   #7
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We use a lot of Metler-Toledo load cells. Depending on which weighing model you have, you can get plug in board that support all the major protocols, I have some on Allen-Bradley RIO, some on ethernet, and I believe they support device net and profibus. The base unit usually has a serial port for ASCII output. It may be worth checking into other communication options.


I know the Jaguar, and Lynx models support additional protocols, but I don't think the Panther models do. (not sure about the Panthers)

Copied this from thier web page:
The accuracy of Mettler Toledo’s measurements are supported by a wide variety of communication standards as simple as USB, RS232/485 or Industrial communication standards such as Profibus, Modbus plus, DeviceNet, ControlNet and Ethernet.
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