Typically you take a load cell signal into what is termed a "load cell amplifier". This takes your very low voltage (a few millivolts) signal from the load cell into a standard PLC signal type, usually 0-10v or 4-20ma signal.

Someone from Host may be able to answer and confirm my idea here. Load cells typically have very low voltage output. It can range depending on the cell, but normally it is as low as 10-30mv and some load cells actually can go up to 1-2volts or so (though that is rare and depends on the type). You may be able to use a BRX thermocouple input module and wire the load cells directly to it. Probably not the most proper way to do things, but thermocouples are extremely low voltage signals like most load cells as well (generally thermocouple is 10-30mv from my understanding). You should theoretically be able to take your load cell signal into a thermocouple channel and then do scaling inside the PLC to get your voltage curve mapped to weight.

The easiest way to set your scaling up would most likely be to take your scale unit with the load cell and have 5 or so calibration weights of different sizes, then place the smallest weight on the scale. Record the input voltage the PLC has, and repeat for all your weights. Then in the software, set up your scaling instruction and list your different voltages as points of the scale curve, and tell it what the weight range is that you already know. Should be that simple.

You may also be able to use one of these signal conditioners to change from the extremely low voltage up to a 0-10v or 4-20ma level that can then go into a PLCs standard analog inputs:

https://www.automationdirect.com/adc/shopping/catalog/process_control_-a-_measurement/digital_panel_meters/1-z-8_din_size/dpm3-at-a-h

https://www.automationdirect.com/adc/shopping/catalog/process_control_-a-_measurement/signal_conditioners/universal_input/scu-1400

https://www.automationdirect.com/adc/shopping/catalog/process_control_-a-_measurement/signal_conditioners/programmable_temperature_transmitters_(t-z-c_or_rtd_input)/xth-0-unv

The digital panel meter option from that list above may be a nice solution if you dont want to go straight into a BRX thermocouple module, because the panel meter can scale in the unit so you could make it display the weight right on it. Though just going straight into a BRX thermocouple unit would be the cheapest option by far if it is possible (it should be). A BX-08THM module would be able to do 8 inputs right into the PLC for only $222, much cheaper than any other option I know of.

While these options are not officially a load cell amplifier, it functions the same way, taking a very low millivolt level signal and turning it into a PLC level signal.

edit: here is an actual load cell amplifier if you would like that option instead since it has a nice display readout and costs similar to the other options I listed:

https://loadcellsys.com/product/tle-load-cell-amplifier/

https://loadcellsys.com/product/tlb-rs485-load-cell-transmitter/

What model load cells do you have?

edit: as for how to handle the excitation voltage required for the load cell, many work on 5, 10, and 12 volts and typically have a max voltage of 15 to 18v. This means depending on the model and weight you will be using a standard 5v or 12v power supply could be used to power all your cells.