Help writing plc code for a system with 4 loadcells, 1 junction box, 1 motor

I will be buying the plc and the loadcells in 2 to 3 days and after that the real fun will begin.

I am thinking of buying s7-1200 but im kinda curious. Will it be enough for my loadcells? i mean i will connect my loadcells with a junction box and then will connect it to my plc but i really dont know.

https://www.esit.com.tr/en/load_cells/ssb__load_cell/urun/174
i am thinking of buying 4 of these(2tons) but will my plc give any problems? is it powerful enough? Really dont know :D


How many analog inputs does the S7-1200 have? I don't think any S7-12xx models have more than 2 analog inputs, 0-10V. Is S7-1500 series the same? Maybe you can purchase an add-on module?


Or can the load cells be connected via a network (ethernet/profinet/modbus/etc.)?
 
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The basic model has 2 but they are only 0-10v I believe, you do not need any more, the 4 loadcells are in parallel (summed) but will need to be converted to either a voltage or current output as the load cells only give out mv.
So in the case of an S7 1200 with analogues built in a loadcell amplifier with a 0-10v output would be required. Depends on how much the OP wants to spend, these come in many forms, a simple amplifier with zero & span right up to a more sophisticated controller with step calibration, zero, tare. gross digital inputs & even communications.
I have used these many times but have no idea of the cost as that was done by the engineering buyer.
https://www.lcmsystems.com/LCA15
or here
https://datum-electronics.co.uk/product-category/load-cell-amplifiers/

Edit: By the way, although they recommend using the summing Junction box it is not required, we had them fitted under our vessels & often got damaged by the amount of water & steam in the area, these were supposed to be IP68 but they never proved any better than a Rittal box with a bunch of terminals in so are not strictly required.
 
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Hey, i've been thinking to try and simulate our project. I've bought tia portal and now im in a slump, i dont know which plc to use. i've no idea what kind of a plc should i be using, there are a lot of cpus and they all serve different purposes. What would you guys recommend? i want to use s7-1200 but which one :D
 
Be sure and get a regulated power supply for load cells, that is probably the most important thing when designing load cell weighing system. Spec's on load cells will tell you what voltages they can handle, typically they are like 5-15 volts dc. Load cell will also have a rating like 1mv/volt say at 10,000 pounds, so if you had a 10 volt power supply and put 10,000 pounds on load cells you will get 10 millivolts. Other load cells might say 2mv/volt at 10,000 pounds so you would have 20 millivolts with 10,000 pounds on load cells etc.. The 4 load cell will as you said go to what is called a summing board or junction box this would allow you to balance the 4 load cells individually and then sum them and provide a millivolt or other type of output to go to your PLC analog card or module. To summarize what I said using 10 volt power supply the max millivolt output from a 1mv/volt @ 10,000 pounds load cell would be 10,000 millivolts and in this easy math case 1 millivolt per pound resolution. Also you can check system with a multimeter set on millivolt setting follow above info.
Then do what the other guys above say.

To simplify what they said you enter a set point for PLC to compare with (weight to fill to) PLC will have a compare function and continuously compare what you entered as set point to actual load cell weigh, (every few millisecound or faster. like Parky said you will have to play with it a little once running to get system to stop motor prior to reaching exact weight due to stop time inertia etc..
Good Luck!
 
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