We continue the discussion of ‘nominal’ from the previous post with an example load cell application. Sizing loads cells is easy provided that someone takes the time to do some simple trigonometry and engineering statics calculations.
1) 'Best' is not the goal
2) 'Good enough' is the goal
By good enough I mean that the load cell system should be able to measure/resolve less than 5% of the lowest tension you ever expect to run. While wrapping more (or getting a better load cell) and getting to 1% of the lowest tension might seemlike it is better, it will give you no better practical results. Thus, if the simpler Option A is good enough, then that is what you want. However, if even Option B with the higher wrap angle is not good enough, you must re-iterate on the design. With light weight webs you may need to do more. You could, for example, use 180 degree wraps (pulling up) and light weight carbon fiber roller to get the tare weight down and thus get a smaller more sensitive load cell.
This is not only how we size load cells, but also how we size brakes, motors, cylinders, sensors and much much more.