and in fact how many industrial application work
I would have thought so.
So i would need cells on either side of each idler and try and write code that can compute the overall weight of the package based on a minimum of four load cells and then spit out a single number? Is this what you had in mind?
Dead easy way to do it. Noted that most "electronic" personal ("bathroom") scales now have load sensors in each of four feet and total the readings (probably as an analog addition prior to the ADC). Much
more reliable than mechanical linkages. You can either do this (op-amp as an adder) or feed them into ADC channels (or use an external multiplexer - the Arduino of course has an internal multiplexer and one ADC) and add them up - exactly what microprocessors are so good at.
Doable I guess for a flat conveyor, but mine has side rollers to prevent anything falling off. Therefore i'd need a minimum of 12 load cells to do this.
If you mean slanted rollers, that could be tricky. Vertical rollers would not count.
I should imagine you would attach all rollers in a set to a single support bar and have one load cell under each end. A (pair of) long radius bar(s) parallel to the belt would stabilise it.