pneumatic comparator and solex pneumatic comparator

Principle of pneumatic comparator

• The measurement is made by taking reading using master gauge of known accuracy and comparing with component reading
• It uses a controlled, pressurised jet of air to measure small dimensional variation in the size of component
• The working principle of pneumatic comparator depends on the flow of air between the gauge head and the component being checked

Important characteristics

• Very high magnifications are possible
• It can be used to measure diameters, length, squareness, parallelisms, concentricity,taper, and other geometric conditions.
• Internal dimensions can be readily measured , in other words, while measuring a bore it can reveal complete details of size, taper, straightness,camber and bell mouth etc.
• It is independent of the operator skill

• High pressure air gauging can be done by cleaning the parts which helps to eliminate errors due to dirt and foreign matter.
• As there is no physical contact made either with the setting gauge (or) the part being measured , there is no loss of accuracy because of gear wear.
• Gauging pressures can be kept sufficiently low to prevent part deflection

• Dimensional variations throughout the length of the shaft (or) cylinder bore can be explored for out of roundness, taperness, concentricity,regularity and other similar conditions
• The total life cost of the gauging heads is much less
• It is accurate, flexible, reliable,universal and speedy device for inspecting parts in mass production

• It is best suited for checking multiple dimensions and conditions on a part simultaneously in least possible time.
• It can be easily used for a line measurement of parts as they are being machined and take corrective actions.

Principle of Solex Pneumatic Comparator

Working principle of Solex pneumatic comparator

• This instrument is produced commercially by Solex air gauges Ltd.
• This is generally designed for internal measurement
• But with suitable measuring head it can be used for external gauging also
• The arrangement used in Solex gauge is to pass the high pressure air after filtering through a flow valve

• It consists of a tank in which water is filled up to a certain level and dip tube is immersed into it up to a depth corresponding to air pressure .
• In the Fig it is represented by `H`
• Air is sent at higher pressure than required one
• Some air will leak out from the dip tube and bubble out of water

• And the air moving towards control orifice will be at desired constant pressure `H`
• It is very obvious from Fig that the diameter being measured at any instant is corresponding to the portion against two jets
• To find the concentricity (roundness of any job at any section) The work piece may be revolved around the measuring gauge

• Similarly the diameter can be noted down at several places along the length of bore and thus tapering of hole is determined
• This method is best suited for measuring roundness and taperness of cylinder bores and gun barrel bores
• By having suitable measuring head this can be used for external gauging also

Advantages of Pneumatic Comparators

• Comparators can be checked with out contact with finished surfaces
• This method needs little skill to operate
• No limit to the size of work that can be tested
• Provide a simple and direct method of high amplifications
• Dimensional variations can be controlled with close tolerances

By Lecturer B.Ravikumar Mechanical Engineering