[Physics Class Notes] on Hygrometer Pdf for Exam

An instrument called a ‘hygrometer’ is helpful and acts as a humidity measuring device. This helps to measure the amount of water vapour. This instrument is useful in measuring the water vapour in soil, or air, or any confined space. 

This is an instrument particularly useful for measuring humidity. These types of gadgets are the apparatus that are used to calculate some other quantities such as pressure, temperature, mechanical or electrical change, and the mass of a substance due to the absorption of moisture.

You can find out the values through the right calibration and calculation. If you try to measure humidity, it is only possible through the hygrometer.

Measurement of Humidity

The temperature of condensation can be the option for the measurement in modern electronic devices. The hygrometer measures the humidity of the atmosphere.

The device has certain limitations, and the measuring part is recognized as the dew point.  To measure humidity differences changes, the device is capable enough to capture the reading and operational with the electrical capacitance or resistance.

This is useful in meteorological science, and for measuring the water content in the air. Different hygrometers are used to calculate the accurate value. 

Instruments to Measure Humidity

The very first design of the hygrometer was introduced by Leonardo da Vinci in 1480. He was an Italian Renaissance polymath. A further major development was added after two centuries, and it was completed during the 1600s.

A practical version of the device was invented by Francesco Folli. Also, Robert Hooke had made some contributions to the improvement of the hygrometer. He also had some interest in hygrometers and has shown his contribution with some meteorological devices.  

In 1755, another advanced and modernized version was developed by Johann Heinrich Lambert. He was a Swiss polymath. 

Thermo Hygrometer

A geologist and physicist from Switzerland known as Horace Bénédict de Saussure developed a hydrometer in 1783. The device was capable enough to measure humidity. 

The device was operational on human hair (hair hygrometer). He was the first person to invent a hygrometer.

A massive amount of water vapour can be calculated through a hydrometer. The device is capable enough to measure the volume of air saturation. You know that the volume of air varies significantly by its temperature.

It is proven that air at a lower temperature can hold less mass of water per unit volume. However, this statement is satisfied with hot air. Humidity is the fact that can alter the temperature.

Most instruments, such as thermometer hygrometer can standardize or react to read the relative humidity (RH). Relative humidity can be explained as the amount of water associated with the maximum temperature at a higher temperature with a particular percent.

Digital Hygrometer

1. Capacitive

A capacitive hygrometer is useful and appropriate with other types of electronic sensors. It has not that much accuracy, and so it can be bought at a lower price. The result of humidity in capacitive hygrometers is measured with the help of the dielectric constant.  

This constant is brought from a metal oxide or a polymer material. Proper calibration gives accurate value, and sensors are used, which can measure accurate humidity..

If you miss the calibration, the accuracy of the apparatus is getting a little bit worse (up to two to three-time). The sensors that are used in capacitive are very useful against temporary high temperatures and condensation. 

2. Resistive

The resistive hygrometers use a different method. They measure the value by the alteration in the electrical resistance of a material because of the humidity.

Different types of materials, such as conductive polymers and salts are used in this device. The properties of the material used in this type of hygrometer are very ideal for humidity and temperature. 

It has a combined sensor that can also help to measure the temperature. The accuracy of the output is dependent on resistive material. The sensors of resistive hygrometers are not that good as the sensors of capacitive hygrometers. 

3. Thermal

Thermal conductivity is the primary unit of measurement in thermal hygrometers. This can measure the humidity with the change of thermal conductivity.

4. Gravimetric

Gravimetric hydrometers are capable enough to handle the measurement of the mass of air with an equal volume of dry air. 

It is one type of accurate measurement which helps to measure the right moisture content in the atmosphere. Further, this gravimetric hygrometer is very useful in the UK, US, Europe, and Japan.

5. Optical

Optical hygrometers are used to measure the absorption of light by water. All this process is based on identifying the moisture in the air. Two components are there, such as a light detector and a light emitter. 

The detector detects the light and indicates the humidity of it. This process is based on the law of Beer-Lambert.

Lyman-alpha hygrometer comes under the category of optical hydrometers. Hydrogen is responsible for the emission of Lyman-alpha rays. It detects the light and helps to measure the correct value for the humidity that is present in the atmosphere.