Pressure sensors -Let us understand them.

Oct 24 08:02 2011 Jayprakash Shet Print This Article

In our daily life we come across many instances where we have to measure or control pressure. For example some times when we start our domestic pump,Guest Posting we see that it is not lifting proper amount of water what it used to be. There may be so many reasons. In other way it is not generating enough pressure to push water to the required height.

Many persons have low Blood Pressure. That means heart - our pump - is not generating enough pressure to circulate the blood through our body. Each second we are experiencing pressure from our atmosphere. When we dive in swimming pool we experience the pressure of water on our body.

As far as Industry is concerned there are many instances, when we have to measure or control pressure.

For example in chemical industry, we have to check and control boiler pressure, Tank pressure, Engine oil pressure etc.

How can we measure pressure? There should be some units by which we can measure the pressure. Pressure is always measured relative to atmospheric pressure. We know that our earth is surrounded by an atmosphere most of which, contains Air. Air also has mass and it creates pressure. This will depend where you are. If you are standing on sea shore you will experience more pressure than if you are standing on a tall mountain.

The mass of air at standard gravity creates pressure of 1000 mili bar or 1 bar at sea level. Bar is a unit of atmospheric pressure. It is a pressure when a litter of water is kept as a column which is 10 meter or 1000 cm high and bottom surface area is 1 cm2. The pressure experienced at the surface area of this 1 cm2 is equal to 1 Bar.

In early days this water column or mercury column was used to measure pressure. As we saw earlier, atmospheric pressure depends upon the height from our sea level. As we go up, the pressure reduces. If we go to 1000 meter above the see level, the atmosphere pressure decreases by 100 mili bar approximately.

Same way if we go down the sea, we experience the increase of pressure. But the rate will be much higher as water is 1000 times heavier then air. As we go deep in water, the pressure increases by 1 bar for each 10 meters.

The pressure can be of three types. Absolute, Relative and Differential.

Absolute Pressure - This is the pressure referenced to a sealed, vacuumed volume.

Relative Pressure - This is a pressure which is referenced to atmospheric pressure.

Differential Pressure - This is referenced to each others difference of pressure.
In early days the pressure used to be measured by using a diaphragm or a bellow. The kind of instrument made from diaphragm was called gauge. The diaphragm is connected to a mechanical pointer such that the movement created by pressure on diaphragm is shown on a dial by the pointer. Though it employs such simple technology, they are used today also.

By the advent of electronics, the sensing technology is also changing fast. The instrument and sensors are becoming sophisticated as well as size is shrinking. More and more micro technology is used to make sensors better and better and also with the increasing accuracy.

As we have seen above, the pressure sensors also, over the period, have developed in consistency with the latest technology. To measure different kind of pressure, we have different kinds of sensors.

1. To measure pressure referenced to atmosphere we have gauge pressure sensors. This kind of pressure sensor provides zero output at atmospheric pressure. These sensors are generally used where you want to measure both negative (vacuum) and positive (pressure) outputs.

2. Differential pressure sensors measure the difference of pressure at two ports. This kind of pressure sensors are generally used for measuring pressure of Liquids and Gases.

3. Absolute pressure sensors are used to measure pressure in unipolar output only. That is to say, they provide output only in one direction, not the both, negative and positive.
4. Vacuum pressure sensors are generally used to measure vacuum created in a chamber. These sensors give zero output at atmospheric pressure. The output will increase as the vacuum increases.

5. We have also got pressure sensors that measure atmosphere pressure. These are called barometric pressure sensors. The output of these sensors is “inches of Mercury" whose unit is Hg.

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Jayprakash Shet
Jayprakash Shet

Jayprakash Shet is an expert in designing & developing latest microcontroller based consumer & industrial electronic products. For USB relay board & other electronic kits please visit

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