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I've contacted a few load cell suppliers and none of them appear to be particularly enthusiastic about running load cells directly into a PLC. I can do it, they say, but they all recommend that I first go into a summing box/weight controller and then analog out to the PLC. None of them have given me a good reason for doing this. It may be that they just want to sell me the electronics, but I want to make sure there isn’t a valid performance related reason to avoid going directly into a PLC. I like the simplicity of the concept, I avoid dueling digital displays, and I can see each individual load cell. App accuracy is of paramount importance. Any help would be greatly appreciated!
App info
(3) 500 lb load cells, S type. 1500 lbs total
2 mV/V
0-15 VDC excitation
App accuracy requirement of the load cell sum is +/- 1 lb
The three load cells will be supporting a tank. I would like to run all three load cells into a thermocouple/mV module (Allen-Bradley Flex Logix 1794-IT8). I’ll sum the load cells in the PLC. I would like to monitor each individual load cell as well as the sum of all three. I will be datalogging the load cell outputs and the sum will be used in a program with multiple/changing setpoints that controls a process.
The load cells are to be in a class 1 div 1 room.
The PLC is not.
The cables from the load cells to the PLC will be 25-50 feet long.
I imagine I'll need an intrinsically safe barrier between the power supply/PLC and the load cells.
App info
(3) 500 lb load cells, S type. 1500 lbs total
2 mV/V
0-15 VDC excitation
App accuracy requirement of the load cell sum is +/- 1 lb
The three load cells will be supporting a tank. I would like to run all three load cells into a thermocouple/mV module (Allen-Bradley Flex Logix 1794-IT8). I’ll sum the load cells in the PLC. I would like to monitor each individual load cell as well as the sum of all three. I will be datalogging the load cell outputs and the sum will be used in a program with multiple/changing setpoints that controls a process.
The load cells are to be in a class 1 div 1 room.
The PLC is not.
The cables from the load cells to the PLC will be 25-50 feet long.
I imagine I'll need an intrinsically safe barrier between the power supply/PLC and the load cells.