The barometer has been a popular device in the world of meteorology since the 19th century. It’s basically used to measure the atmospheric pressure, which is one the key parameters for weather forecasting. To understand its functioning and purpose, let’s take a look at what it’s used for and how it works…
What is a barometer used for?
The barometer is primarily used for weather forecasting purposes. The barometric pressure along with the changes in pressure over the course of time are used to create weather maps after data is collected across multiple weather stations. As well as this, barometers are also used in aircraft for calculating the flight altitude. In this case, a barometer is referred to as an altimeter because it is calibrated to measure altitude using the atmospheric pressure readings. Barometers are also used in scuba diving to keep a check of the air content within the tanks of divers. To understand the barometer better, let’s explore its working principle, types and method of operation.
How does a barometer work?
Although the working mechanism may vary with regards to the type of the barometer, the principle of its operation remains the same. A barometer measures the current atmospheric pressure, which varies as the altitude changes. The reference point for this change is the standard atmospheric pressure which is the pressure at sea level and equates to pressure exerted by 760mm of Mercury (Hg) at 0 oC. For a particular temperature, we can observe that as the altitude increases, atmospheric pressure drops as air becomes thinner and exerts lesser pressure. The reverse is seen, as we descend from a higher altitude.
How to use a barometer?
You can actually use a barometer yourself, in your home, for weather forecasting. Depending on the type of barometer, you can measure the pressure and apply the same analysis to get weather readings. For the aneroid or analogue version, you need to calibrate it on the basis of your near weather station. This is done by turning a clock like dial and once you have matched the local barometric pressure, you are good to go. With digital barometers, this is done automatically for you. With the calibration done, you simply need to read the change in pressure and the direction of the change. Measurements are normally in inches or millibars and are generally ranging between 28 to 31 inches. Since the change in pressure is needed, readings will have to be taken after a regular interval of few hours to observe the change.
Types of barometer
There are many different types of barometers but broadly speaking, they can be divided into 3 categories: i) Mercury ii) Aneroid iii) Digital
Mercury: It is the simplest and the most traditional form of the barometer. Also called the Torricellian barometer, it consists of an inverted tube placed in a Mercury bath. This barometer measures the change in the pressure by the rise or fall of the mercury level in the tube. 760 mm or 29.92 inches of Hg is considered to be the standard atmospheric pressure. As we gain altitude, mercury level falls in the tube because a less pressure is applied by the atmosphere on the mercury bath so less amount of mercury is pushed in the tube. The vice versa is also true as well.
Aneroid: Aneroid is the common choice of barometers for use in homes since mercury is poisonous and an unnecessary hazard to have in homes in large quantities. Instead of mercury, aneroid barometers have a small air tight metal box that moves inwards or outwards depending on the change in pressure. At higher pressures, the box is pushed inwards while at lower pressures, it is released and moves outwards. A spring is attached to the box which is also connected to a needle. The movement of the needle corresponds to the pressure changes which are displayed on the dial.
Digital: Digital or electronic barometers are the modern options and are now being used in many sectors. They normally have sensors that can determine the altitude and by using a strain gauge, it can provide atmospheric pressure readings. The principle here is that the atmospheric pressure applied to the diaphragm attached to the strain gauge changes its resistance. This leads to a change in the voltage signal which is amplified and displayed to the user in terms of pressure.
How to read a digital barometer?
Reading a digital barometer is pretty straightforward. You will get a digital display of the readings. It will provide clear indications of rise and fall of the pressure by displaying either the rising status or the falling status. It will further have a graph called barograph that can display previous pressure trends. All this information can prove to be helpful in developing a keen sense of the weather changes as it can serve as your own mini weather station.
How to read an aneroid barometer?
In aneroid barometers, there are two needles present. One displays the barometric pressure reading while the other is the manual hand. You need to tap the glass of the dial to make the barometric needle move and show the change in pressure. The purpose of the manual needle is help track the changes in the pressure.
Barometer needle not moving ?
There are certain cases where the needle of the barometer will not move. We will briefly identify some of these cases and understand their reasoning. The most common reason for the needle not moving is that the glass of the dial has not been tapped. This is a mechanism that aneroid barometers have that you need to tap the glass to make the needle move. If you have tapped the glass and still the needle does not move then the barometer needs to be inspected.
It is possible that the spring of the needle has become detached and the needle is therefore no longer aligned with the pressure changes. If everything is in order and the correct process is being followed yet the needle is still not moving then that means steady weather because if the weather is expected to remain the same then there would be no pressure changes.