An electronic device

Electronic component

An electronic component is a basic electronic element and may be available in a discrete form having two or more electrical terminals . These are intended to be connected together, usually by soldering to a printed circuit board, in order to create an electronic circuit with a particular function...

 analogous to a thermostat

Thermostat

A thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...

 but which responds to relative humidity

Relative humidity

Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...

 not temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

. Humidistats are utilized in a number of devices including dehumidifiers, humidifiers, and microwave ovens. In humidifiers and dehumidifiers the humidistat is used where constant relative humidity conditions need to be maintained such as a refrigerator

Refrigerator

A refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room...

, greenhouse

Greenhouse

A greenhouse is a building in which plants are grown. These structures range in size from small sheds to very large buildings...

, or climate controlled

HVAC

HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...

 warehouse

Warehouse

A warehouse is a commercial building for storage of goods. Warehouses are used by manufacturers, importers, exporters, wholesalers, transport businesses, customs, etc. They are usually large plain buildings in industrial areas of cities and towns. They usually have loading docks to load and unload...

. When adjusting the controls in these applications the humidistat would be what is being set. In microwaves they are utilized in conjunction with "smart cooking" 1-button features such as those for microwave popcorn

Popcorn bag

A microwave popcorn bag is an engineered, enhanced, sealed paper bag in which un-popped popcorn is sold for the purpose of cooking popcorn in a microwave oven. These bags and their contents are sometimes referred to as microwave popcorn...

. Humidistats employ hygrometers

Hygrometer

A hygrometer is an instrument used for measuring the moisture content in the environmental air, or humidity. Most measurement devices usually rely on measurements of some other quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed...

 but are not the same. A humidistat has the functionality of a switch

Switch

In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....

 and is not just a measuring instrument

Measuring instrument

In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...

like a hygrometer is.