The main difference between a hygrometer and a psychrometer

 The main difference between a hygrometer and a psychrometer is how they measure humidity, though both are used to determine the relative humidity of air: 

Hygrometer

A hygrometer is a device that measures humidity, and there are many different types of hygrometers. For example, a capacitive hygrometer can measure the moisture content of tablets. 

Psychrometer

A psychrometer is a type of hygrometer that uses two thermometers to measure humidity. One thermometer has a dry bulb, and the other has a wet bulb. The wet bulb is wrapped in a damp cloth, which causes it to read cooler than the dry bulb. The humidity reading is calculated by comparing the temperatures of the two thermometers.

 

Here are some other differences between hygrometers and psychrometers: 

Usage: Hygrometers are more commonly used in domestic settings, while psychrometers are more commonly used in medical institutions and industrial settings because they are more accurate. 

Maintenance: Psychrometers are battery-free, portable, and require little maintenance.