Principle of Measurement in Hygrometers

Hygrometers are instruments used to measure humidity in the atmosphere. There are different types of hygrometers, but the most commonly used principle of measurement is the change in resistance of salts with humidity.

How does it work?

The sensing element in a hygrometer is usually made up of a salt that can absorb moisture from the atmosphere. When the salt absorbs moisture, its electrical resistance changes. This change in resistance is proportional to the amount of moisture absorbed by the salt.

Types of Hygrometers that use this principle

1. Hair hygrometers: These hygrometers use human or animal hair as the sensing element. The hair expands or contracts as it absorbs or loses moisture, which causes a change in its electrical resistance.

2. Capacitive hygrometers: These hygrometers use a thin film of a hygroscopic material as the sensing element. The film absorbs moisture from the atmosphere, which changes the capacitance of the sensor.

3. Resistive hygrometers: These hygrometers use a ceramic material coated with a hygroscopic salt as the sensing element. The resistance of the ceramic material changes as the salt absorbs moisture from the atmosphere.

Advantages and Disadvantages

Advantages:
- Relatively simple to use and maintain
- Can provide accurate measurements over a wide range of humidity levels
- Can be used in a variety of settings

Disadvantages:
- Can be affected by temperature changes
- Requires calibration to ensure accuracy
- Can be affected by contamination or damage to the sensing element

In conclusion, the principle of measurement in hygrometers is the change in resistance of salts with humidity. This principle is used in different types of hygrometers such as hair hygrometers, capacitive hygrometers, and resistive hygrometers. While this principle has its advantages and disadvantages, it remains a widely used method for measuring humidity.