On some important quantities influencing proper functioning of the differential pneumatic comparator

Back-pressure air gauging is an effective and practical way of controlling machine parts in large-scale production. It is a non-contact measuring technique based on the flapper-nozzle effect. The proper functioning of a differential pneumatic comparator depends on several geometric parameters as well as flow conditions inside the device. The main problems of this controlling technique are the fouling of the measuring nozzle head and changes in the accuracy of the comparator. This paper examines the influence of the supply pressure, the diameter of the orifice in the measuring branch, and the axial distance in the flapper-nozzle area on pneumatic comparator performance. In a way, we are trying to optimize the performance of a given pneumatic comparator with respect to the tolerance field for which it is intended. The size, strength, and position of the vacuum in the flapper-nozzle area depend on the supply pressure and the axial distance between the measuring nozzle outlet cross-section and the workpiece surface. For a certain combination of these two parameters, we can influence the vacuum quantities. A pneumatic sensitivity of a comparator can be increased by increasing the supply pressure. The greater accuracy of the back pressure air gauge, the smaller the application range, i.e. the tolerance field that we can control with a given device