Pressure Measurement

# What is a barometer and what is it used for?

A barometer is a pressure sensor that is used to measure atmospheric pressure. This device is very sensitive, and they are capable to measure the absolute pressure. A barometer can measure the pressure exerted by the atmosphere with the help of water, air, or mercury. The atmospheric pressure would change according to the distance above or below the sea level, the barometer can also be used to measure altitude. The major types of barometers that are widely used are mercury and aneroid barometer. The barometer can measure the atmospheric pressure in units of measurement called atmospheres or bars.

### How to read the barometer and what does it mean when a barometer is rising or falling?

Before reading the barometer it must be slightly tapped, while checking the needle we must gently tap the glass and must check which way the needle moves. We can determine the increase and decrease in pressure by using a barometer and if the needle isn’t moving then the barometer is holding steady

The barometer is a device that can measure air pressure the rising barometer indicates the rising air pressure and the falling barometer shows the decrease in air pressure.

### What are the types of barometer and how does it work?

Mercury barometer

A mercury barometer consists of a glass tube, and this glass tube is closed at one end and it has an open mercury-filled reservoir at the base. The vacuum will be created on the top of the tube because of the weight of the mercury, so if the mercury level falls in the glass tube then the vacuum is created in the top. So basically a mercury barometer operates by balancing the mercury weight in the glass tube over the weight of the atmospheric pressure.

The mercury level in the glass tube increases if the weight of the mercury is less than the atmospheric pressure. The mercury level would decrease if the weight of the mercury is greater than the atmospheric pressure. The mercury level would change constantly till the weight of the mercury in the tube is equal to the weight of air above the reservoir. By using a ruler we can measure the rising and falling of mercury.

Aneroid barometer

The aneroid barometer can be considered an advanced barometer because it doesn’t have the disadvantages of a mercury barometer. The mercury barometer is fragile and it won’t work properly if it is disturbed by outside motion. The aneroid barometer doesn’t use any liquid and it is really compact. The portability of the aneroid barometer makes it a suitable device to use at sea or in the field.

An aneroid barometer has a sealed chamber and it would expand and contract according to the atmospheric pressure around it. By using certain mechanical tools we can measure how much the chamber expands and contracts. The aneroid barometer consists of a flexible walled evacuated capsule, this wall would deflect according to the changes in atmospheric pressure.

Water based barometer

This type of barometer has a glass container with a sealed body and it will be half-filled with water. A narrow spout connects to the body below the water level and rises above the water level and the narrow spout is open to the atmosphere. So when the air pressure is lower than it was at the time the body was sealed, the water level in the spout will rise above the water level in the body. When the air pressure is high then the water level in the spout will drop below the water level in the body.

### What are the applications of barometer?

• It is used to measure weather
• Science and industry
• It is used in watches and smartphones
• This device can be used to check the altitude
• Aneroid barometers are used in portable instruments
• The aneroid barometer is used in aircraft altimeters