Skip to main content

PNEUMATIC COMPARATORS AND ITS WORKING

 In recent years, pneumatic comparators have been extensively used specially in automatic size control. They are cheap, independent of the contact pressure, and simple to operate. Besides, this form of comparator is free from mechanical wear. However, pneumatic comparators are sensitive to temperature and humidity changes and their accuracy may be influenced by the surface roughness of the parts being checked. The magnification of this type of  comparator is as high as 10,000. 

The operation is based on the fact that if air under constant pressure escapes by passing through two orifices the air pressure in space between them is  dependent on the cross-sectional area of  the orifices. If one of them is kept uniform, the pressure will vary according to the size, of the other.

In the diagram, The pipe l expands in tube 11 and maintains a constant head of water H , excess air escaping as bubbles. Air from 11 passes through control jet 3, and finally escapes through the measuring jet at 6. The pressure in pipe between control jet 3 and measuring jet 6 will depend on the size of the orifice at 6, i.e . upon the gap "d" which is controlled by the distance between the measuring face and table, and is reflected by the height of  a column of liquid in manometer tube 8 on the face of the guage. The scale 9 is so calibrated that a head difference "h" indicate differences in the gap "d" magnified several hundred times. 


Pneumatic comparators

Other Common Types Of Comparators :

* Mechanical Comparators. 

* Electrical Comparators. 

* Optical comparators. 

Labels:

Comments

Post a Comment

Popular posts from this blog

Advantages And Disadvantages Of Air Refrigeration System :

 Advantages Of  Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of  Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content. 
Post a Comment
Read more

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of  detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of  a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of  the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of  electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a  roll. The objec...
Post a Comment
Read more

THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the  turbine constant at part load and hence this method of governing is called "Throttle Governing".  Construction : Throttle governing system consists of  a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber.  Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movemen...
Post a Comment
Read more