An outdoor thermometer is a scientific instrument that reads the temperature of the air outside. There are three main kinds of outdoor thermometers: the bulb thermometer, the bimetallic strip thermometer, and the digital thermometer. Each kind operates in a slightly different manner, but all work to allow people to read the temperature outside.
A bulb outdoor thermometer is the most basic type. It is typically made of glass and filled with mercury. As the temperature rises, the mercury changes in volume. As a result, the mercury moves up the glass tube. In the alternative, if the temperature goes down, the mercury takes up less space in the glass tube and goes down.
Although a mercury-filled outdoor thermometer is an accurate way to tell the temperature, it can be problematic. Mercury is a toxic substance. If the thermometer breaks and the mercury leaks out of the glass tube, it must be cleaned up properly to prevent serious medical issues.
The bimetallic strip outdoor thermometer looks like a dial. It is made from a spring-like coil. The coil is comprised of two kinds of metal pieces that are attached in a way to gauge the temperature outside. It works when the two metal pieces expand or contract at different rates. For example, if one piece of metal retains heat, the coil will be forced to expand, and the hand of the dial will creep upward. If the temperature drops, the metal will cool faster, contracting the coil, and moving the dial hand downward.
The digital or electronic outdoor thermometer is the most modern and is also considered to be the most accurate. Inside the thermometer is a thermoresistor that alters its resistance according to the temperature. Next, a sensor on the micro-computer reads the temperature and digitally displays it.
There are countless style options for all kinds of outdoor thermometers. They can be discreet or quite large, such as the ones outside banks. They can be hung away from the house, suctioned to a window, or staked in a garden. While digital outdoor thermometers may require a new set of batteries from time to time or a separate power source, a bulb or dial thermometer will not. In addition, some light up at night, making it easy to read the temperature when it is dark outside. Some models have only one sensor, but more expensive models have multiple sensors that can be placed in various areas on the property and lend to the most accurate readings.
Regardless of the type of outdoor thermometer, placement is one of the most important factors for an accurate reading. It should be in a shady area with plenty of air flow. In addition, it should be placed at least five feet (1.52 m) above natural ground, such as grass or dirt—not above asphalt. In fact, it should be located no closer than 100 feet (30.5 m) to a street or to concrete. Placing it near sprinkler systems or tall buildings may cause an inaccurate reading as well.