How Weather Gadgets Work

In many ways, our lives are defined by temperature -- and being able to accurately measure temperature gives us an exceptional advantage. It lets us know how much to heat or cool our homes or how much longer we need to cook a poultry dish without making everyone sick. It helps us diagnose ailments and know whether to grab a scarf on the way out the door in the morning.

Classic bulb thermometers contain a liquid that changes volume with temperature fluctuation since liquids take up less space when they're cold and more when they're warm. Most bulb thermometers contain mercury, which is largely immune from boiling and freezing. Sealed inside a tube, the liquid rises and falls with the surrounding temperature. Measured lines on the tube mark the temperature at which the mercury would need to be to reach that level.

Bimetallic thermometers gauge temperature with two pieces of bonded metal that expand or contract with heat. These gadgets typically show up in ovens and refrigerators, activating an electric circuit at the appropriate temperature. Electric thermometers use tiny computerized parts called thermoresistors to measure temperature. Thermoresistors resist the flow of electricity through a circuit at different levels depending on temperature. 

Naturally, if you want to know the temperature on your back porch, you'll need the thermometer to actually be located on your back porch. You can't leave it on your dresser and expect it to tell you the outside temperature. Or can you?

Luckily, we live in an age of wireless transmitters. With a wireless indoor/outdoor thermometer, you can actually peek out from underneath the warm covers, reach over to the nightstand and check room temperature, as well as outside temperature. This is because, in addition to the inside thermometer housed in the gadget right there beside you, there's another one outside transmitting data to the main unit. This works in much the same way a baby monitor receives data on one end (in the baby's room) and allows it to be heard on a unit elsewhere in the home.

These remote sensors typically work within a range of around 100 feet (30 meters). With many models, you can use additional remote sensors to gauge the temperature at even more locations. With this $20 or so technology and a few fresh batteries, you don't have to roll out of bed to know exactly what the temperature is in your room, the garage, the basement and the yard.

In solving a murder, a detective compiles a number of elements to determine the murderer and the method. It's much the same with the weather, except meteorologists attempt to uncover a future event, not a past crime. ­

­To forecast what tomorrow will bring, weather detectives gather evidence: air temperature, air pressure, humidity, wind speed and rainfall. In the last section, we covered thermometers, but how do the rest of these weather forecasting devices work?

Barometer: This device measures air pressure with a glass tube and a small quantity of mercury, much like a thermometer. This time, however, an airless tube is inserted into a plate of mercury. The top of the tube is sealed, while the bottom is open. Air pressure pushes down on the mercury, which in turn pushes it up the tube against the vacuum in the tube. In this regard, a basic barometer works like a scale. Air pushes down on one side, mercury rises on the other. By measuring the position of the mercury in the tube, we can determine current atmospheric pressure.

Hygrometer: If you want to monitor the humidity outside or inside your home, then this is the gadget for you. A psychrometer uses a wet-bulb and dry-bulb thermometer. The user simply directs air over the two bulbs and checks the temperatures. The difference between the two reveals humidity. Dew point hygrometers use a cooled metal plate. Whatever the metal's temperature is at the point of condensation is the dew point. Electrical hygrometers measure moisture-related changes in electrical resistance through a semiconductor. Finally, mechanical hygrometers actually use human hair (or similar tissue) to determine humidity. Since hair expands or contracts depending on humidity, these machines grip the hair tightly and register minute changes in tension.

Anemometer: Often mounted beneath weather vanes, which determine wind direction, anemometers typically measure wind speed with either a small propeller or a kind of pinwheel with cups on the end. Sonic anemometers transmit ultrasonic waves between two pairs of transmitters. These stick up in the air like antennae, several inches apart from each other. Wind passing through this space will either speed up or slow down the ultrasonic waves. The anemometer records these changes to determine wind speed, direction and pressure.

Rain collector: These gadgets can be as simple as a measuring cup placed outside during precipitation. More advanced models record precipitation mechanically, automatically emptying at preset levels.

If these gadgets won't satisfy your weather obsession, keep reading to find out what the pros use.

The gadgets on the previous pages allow people to observe the key atmospheric levels that affect weather. However, if you're willing to invest between $2,000 and $4,000 into your passion for meteorology, you can actually purchase a professional weather station.

There are essentially two varieties of professional weather stations: modular and all-in-one designs. Modular systems consist of mounted clusters of electronic sensors: thermometer, barometer, hygrometer, anemometer and rain collector. In addition to these sensors, models can also boast an ultraviolet light sensor, a solar radiation detector and a visibility sensor. All-in-one weather station designs bundle the sensors in a single, streamlined housing.

Professional weather stations involve far more than just a high-tech assembly of weather gadgets -- they also include the programming and equipment necessary to catalog weather statistics and analyze collected data. Users can even program these systems to alert them of hazardous weather conditions.

The data from a professional weather station can be exported in a number of ways. You can network it with other stations or integrate it into existing networks. The data can be streamed to multiple recipients. And just because you dropped a few grand on your weather station doesn't mean you have to mount it on top of a building. Portable and vehicle-mounted versions are also available.

These systems are typically employed by the likes of airports, construction companies and emergency rescue departments, but there's nothing stopping you from operating one on your own property.

Explore the links on the next page to learn even more about gadgets.