Pneumatic Comparators
Pneumatic Comparator
Pneumatic Comparators uses air as a means of
magnification in metrology. This was originally developed by the Solex Company
in France for the calibration of carburettors.
The first application was the checking of the bores of
motor-car cylinder blocks. Now it is almost used in production shop for this
purpose.
Working Principle:
The Pneumatic Comparator is based on Bernoulli’s
theory. The principle of working of a Pneumatic comparator is shown in figure.
Air at a low (1,5kg./cm2) but constant pressure, ps, is supplied through a
small jet ‘c’ into an intermediate chamber and then pass through a second
orifice gauging jet ‘G’ to atmosphere.
Working Principle:
The component whose dimensions to be checked is placed
below the gauging jet with some air gap as shown on Fig. The amount of air
escaping through gap between work piece ‘p’ and gauging jet ‘G’ will depend
upon the gap h. The gap h will affect the intermediate pressure recorded by the
manometer “M”. If the gap ‘h’ is large, pressure recorded would be small. On
the other hand if the gap ‘h’ is small, pressure would be higher.
The gap ‘h’ initially set with the help of known
standard usually slips gauges. The component whose dimensions to be checked is
placed by removing the slip gauges. If the component has variation in size than
the gap ‘h’ will increased or decreased. This will cause to change in
intermediate pressure, and will change in the manometer reading. The manometer
is calibrated directly to read linear scale.
Advantages:
·
High Accuracy
·
High Magnification
·
Air jet used to clean the dust
·
They are the best for checking the ovality,
straightness, flatness, squareness, roundness, taperness and circular bores
Disadvantages:
·
Need of Auxiliary Equipment’s
·
Large Size
·
Non-Uniform Scale
·
Not Portable
·
Their accuracy will also affected by temperature and
humidity
