If it was not so dusty, hot, sticky, humid and generally hostile to sensors, more businesses would be making sensors into measurements.
There are many companies making sensors, but only a few make measurements which have useful accuracy, reliability, repeatability and reproducability on your process.
Knowing the limitations of each technology, and knowing when to shoot the design engineer, are lessons learned by having been there, and having done that.
Typical application problems are:
Caliper sensors that drift or build up:
Beta sensors which drift from standardise, are prone to non-linear averaging, find static a problem and attract moisture.
Optical sensors which like the laboratory but not that dust, humid machine environment.
Color sensors which are furnish, distance and temperature sensitive.
IR sensors which do not like recycle, pigments and small variations in recipe.
Microwave sensors which find small temperature changes problematic.
X-Ray sensors used for the wrong product, on the wrong grades and in the wrong location.