Advantages and disadvantages of pneumatic instruments :- Although we commonly use current to relay information, some critical process measurements use compressed air to transmit information from one point to another, an example of this could be a petroleum refinery. Some applications use pneumatic devices that will not work well with 4-20 mA current signals due to safety concerns. Pneumatic instruments still find wide applications in industry, although it is rare to encounter fully pneumatic control loops. One of the most common applications for pneumatic control system components is control valve actuation. Not only is compressed air used to create actuation force in many control valve mechanisms, it is still often the signal medium employed to control valve position. In most cases this pneumatic signal is generated by a device called an I/P transducer or current-to-pressure converter, which takes a 4-20mA control signal from the output of the electronic controller and transmits that information as a pneumatic 3-15 PSI signal translates for the Positioner or actuator of the control valve.
Below is an example of a pressure transmitter used in a pneumatic instrumentation system.
Let us now look at the advantages and disadvantages of pneumatic tools.
Disadvantages of pneumatic instruments
- Sensitivity to vibration, changes in temperature and mounting position that can affect calibration accuracy to a greater extent than electronic equipment.
- Compressed air is an expensive utility that is much more expensive per equivalent watt-hour than electricity which makes the operating cost of pneumatic devices far higher than electronic ones. The installed cost of pneumatic instruments can be quite high, given the need for special materials, such as stainless steel, copper, or tough plastic tubes, to carry air and pneumatic signals to distant locations.
- The volume of air tubes used to transmit pneumatic signals over distances acts as a low-pass filter, naturally reducing equipment responsiveness and thus responding quickly to changing process conditions reduces its ability to do so.
So with the above disadvantages, why are pneumatic instruments still in use today ?
The main reason may be due to legacy so facilities that use these pneumatic instruments and keep them in good working condition will not see the need to replace them as in most cases removing the old tubing, installing new conduit and it costs labor to configure the new one. (Expensive) electronic equipment is often not worth the profit.
Advantages of pneumatic instruments
- Internal protection of pneumatic field equipment. Appliances that do not run on electricity cannot generate an electric spark. This is extremely important in graded industrial environments where explosive gases, liquids, dusts and powders are present.
- Pneumatic instruments are also self-cleaning. The continuous bleeding of compressed air from the vent port in the pneumatic relay and nozzle acts as a natural clean-air purifier for the inside of the equipment, preventing dust and vapor infiltration from outside with little positive pressure inside the equipment Can you Pneumatic devices mounted inside large enclosures along with other equipment protect them all by providing positive pressure air purification for the entire enclosure.
- Some pneumatic instruments can also operate in high temperature and high radiation environments that can damage electronic equipment.
- Pneumatic instruments can operate on compressed gases other than air. This is an advantage in remote natural gas installations, where natural gas is sometimes used as a source of pneumatic “power” for equipment. As long as there is compressed natural gas in the pipeline to measure and control, the equipment will work. No air compressor or electrical power source is required in these installations. All you need is a good filtering device to prevent contaminants in natural gas (dirt, liquids, debris) from causing problems within the sensitive equipment system.
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