I don’t know a suitable link but googling the question will come up with some information. I have a basic knowledge of various systems on both passenger and freight vehicles. Passenger vehicle brake systems that vary the brake force with changes to passenger loadings are all the same and use the air pressure in the air secondary suspension to determine the passenger loading. An air pressure signal is taken from the air suspension at each of the vehicle and and fed to an averaging valve to determine the passenger loading. This average pressure is fed to the brake control unit and varies the Brake Cylinder Pressure to achieve the same deceleration rate regardless of passenger loading. For freight vehicles there are many different systems. Where the vehicle loading is fairly constant because they carry the same commodities there may be an empty/loaded changeover system. This could be a manual lever or an automatic system. The automatic system operates when the bogie suspension springs deflect when the wagon is loaded and open a pneumatic valve fitted alongside the spring. The manual lever will either change the Brake Cylinder pressure from tare to laden values or bring into use another Brake Cylinder to increase the brake force. The air signal from the automatic device will work in the same way at the manual lever but I think I have heard of examples where the mechanical advantage of the rigging is increased. Load dependent braking systems on freight vehicles will be used where the commodities and/or extent of loading varies and will require a bogie mounted sensor that provides an air signal proportional to the spring deflection. I am not familiar with these systems but I believe that these always vary the Brake Cylinder pressure in the same was as passenger vehicle. This is a simplified description and more details will be available on the manufacturer’s websites.
