Thermostats
Thermostats use a wide variety of sensors to measure the heat in a house. The most complicated modern versions use an electric current that changes its patterns and strength based on the temperature, but there are also many mechanical varieties. One mechanical version uses a fluid that expands and contracts based on heat levels. Since this system centers on movements made by a fluid, it is known as a hydraulic thermostat.
A thermostat is designed to operate a heating system within a house or building. Thermostats allow users to see what the current temperature is and what the temperature can be raised or lowered to. By turning the dial, the heat of the building can be controlled to a certain extent. This means that the thermostat uses devices to sense the heat of the air accurately and send signals to the heating systems in the house.
Hydraulic Components
Hydraulic thermostats use what is known as a "thermally expansible fluid." This is a highly reactive fluid that swells as the heat rises and shrinks as the heat falls. This fluid is contained within a capsule inside the thermostat, and a light metal rod is extended into the capsule. As the fluid rises, the rod is pushed up, which affects the thermostat dial.
This thermally expansive fluid needs to be very tightly contained--if any escapes, it severely compromises the readings of the thermostat. Very tight seals are placed to contain the fluid inside the capsule. The rod is fitted with a spring and lock system precisely made to react with the fluid, but natural fall back down into place as the fluid shrinks.
Variations
There are many additional electrical components to the thermostat. Most thermostats need to be programmable, so that schedules can be set up to increase or decrease the heat throughout the day. Many thermostats even include weekly schedules so that heat patterns can be set up to differ on weekends or other days. Modern thermostats have digital readings that provide detailed information
The most common types of thermostats use electrical or mechanical versions. Electrical thermostats use low electrical currents that change based on temperature, allowing very definite readings, while mechanical sensors, like the hydraulic version, use moving parts to accomplish the same task. Some mechanical versions use metallic strips that bend in the heat, or particular gases that are especially heat-reactive.