Instrument used to measure atmospheric pressure

 

What type of instrument is used to measure atmospheric pressure?

Instrument used to measure atmospheric pressure, you will come across to learn about pressure measurement devices/ instrument used to measure atmospheric pressure. So pressure measurement is very important thing in industries like measuring steam pressure coming from boiler or in oil and gas fields. It is important thing so as to avoid any leakages and explosions. Also it is not only required in industries but in our day to day life as well as  we need to closely monitor the pressure in our car tyre or gas filled in our car as a fuel. 

So the first thing  is that  what is pressure and its units?  Then we are going to see the second topic that is pressure measurement and also we are going to see few terms related to pressure measurement. Then comes pressure transducers. And the last thing we are going to see few pressure measurement devices in detail, about how they work, what is working principle behind. 

Instrument used to measure atmospheric pressure

what is pressure ?

 In simple words it is the force acting per unit area. It says that it is the amount of force acts on unit area. 

what are the units of pressure measurement?

 The standard unit for pressure is the Pascal, which is Newton per meter square. There are few more units of pressure used commonly which is bar and psi which means pound per square inch. 

Before moving to actual pressure measurement devices let us first understand few topic so first one is pressure measurement is basically divided into two types; that is static and dynamic. when pressure source is constant that is air pressure in our car tyre or a balloon filled with air this type falls under static pressure but when we are measuring fluid pressure in which fluid is not static but it is moving then it is called as dynamic. Measuring pressure of gas pipeline or water pipeline are the examples of dynamic pressure measurement.  

Next term to understand is that, all pressure measured is a relative term. Depending upon which measured pressure is divided into three types that is absolute pressure, gauge pressure and differential pressure. When pressure is measured relative to the zero or a perfect vacuum it is known as absolute pressure. When we measure a pressure relative to the atmospheric pressure it is called as gauge pressure and at the last when we measure the pressure difference between two points then it is called as differential pressure. 

Pressure transducer is a device that converts one form of energy into other form. So we can use this device for pressure measurement since it converts one form of energy into other we can use this to convert pressure energy into the mechanical or electrical signals and these signals can be measured. So depending upon the output signal these transducer are divided into two types first one is mechanical and second is electrical.  

Few examples of mechanical transducers are bourdon tube and bellow. In electrical transducers pressure energy is converted into electrical signals. Few examples of electrical transducers are strain gauge, capacitance gauge, piezoelectric gauge. 

Lets see how bourdon tube gauge works?

They are classified as mechanical pressure measuring instruments, and thus operate without any electrical power. Bourdon tubes are radially formed tubes with an oval cross-section. The pressure of the measuring medium acts on the inside of the tube and produces a motion in the non-clamped end of the tube. This motion is the measure of the pressure and is indicated via the movement. 

Lets see one more device which is U tube-manometer, Manometers are devices in which columns of a suitable liquid are used to measure the difference in pressure between two points or between a certain point and the atmosphere. One of the ends is connected to a pipe container having a fluid (A) whose pressure is to be measured while the other end is open to atmosphere. The lower part of the U-tube contains a liquid immiscible with the fluid A and is of greater density than that of A. This fluid is called the manometric fluid. Manometers works on Hydrostatic Law i.e. hydrostatic pressure exerted by a liquid column. In manometer unknown pressure is determined by balancing it against some known pressure or vacuum.

 Now lets see few of the electrical pressure transducers. 

Strain gauge : If a metal piece is subjected to a tensile stress, the metal length will increase and thus will increase the electrical resistance of the material. The device is designed in such a way that on one side of elastic membrane thin wires of strain gauge are attached and from other side unknown pressure acts. Due to this unknown pressure elastic membrane gets deflected and stretch the strain gauge which eventually changes the resistance of strain gauge. This changes in resistance are proportional to the pressure acting on elastic membrane. 

capacitance transducer : The capacitive transducer or sensor is nothing but the capacitor with variable capacitance. The capacitive transducer comprises of two parallel metal plates that are separated by the material such as air. When the distance changes the capacitance also changes. Now this gauge is designed in such a way that when unknown pressure is applied the distance between plates varies and eventually the capacitance as well and by measuring this changes capacitance we can measure the pressure. 

 electrical transducer that is piezoelectric transducer.

 Piezoelectric device take advantage of the electrical properties of crystals such as quartz. These crystals generate an electrical charge when they are strained. So these crystals are arranged in one conducting element and when pressure to be measured is allowed to strain this conducting element. This conducting element generates some charge which is proportional to the pressure.