In some of multi step production lines there is some system for measuring of internal parts to decrees cultch production.

These Measuring systems will alert to the operator if product was not in the defined range of dimensional tolerances, and will stop the line damaging the products.
According to their technology in our company they separated to four parts:

1- Air gages system:
This system usually use to measure diameter of cylinders or geometry tolerances depend on cylinders (for example coaxilarity, cylendersity, runout , ….)
This system has limited range of measurement and usually use to measure finished parts.
For more information please see special measuring machines.

2- LVDT Tests: (Linear Variable Differential Transformer)
LVDT systems have very good accuracy and also they are long range of measurements they will use in measurement positioning and geometry tolerances of unfinished and finished parts.
But users should design one special system for each product; it is not very good for multi product lines, because for each product they have to buy one set of measuring systems.
For more information please see special measuring machines.

3- 3 dimensional Test CMM: (Touching systems)
Some of coordinate measuring machines (CMM) are designed for inline measurement, these systems will measure all dimensional and geometry tolerances of finished and unfinished parts, they are not depend on the type of product because their measuring programs will change for each product and they will run the measuring program same as CNC machines.
For more information please see CMM department.

4- 3 dimensional Vision Measurement systems : (Vision Measurement)
This type of high technology systems are used to measuring complicated parts same as engine parts of cars and body sides, this systems can measure full 3D and they can identify good products of faulty rapidly, in some of this measuring systems they can measure 30 parts per minute (full inspection) .