What is in a weather station?

A weather station is an instrument that measures the atmospheric conditions. It can be used to measure temperature, pressure and humidity. The most common type of weather stations are those with a barometer sensor.

These instruments have been around for many years but they were not very accurate until recently when new technologies came into play. Today's weather stations use sensors such as thermistors or silicon-based resistors which provide much more accuracy than older technology. They also include other features like wind speed/directional sensing, rain gauge, lightning detector, solar radiation detectors etc.

The Weather station come in different sizes from small handheld weather station to large fixed installations on buildings. Some even combine several functions. For example, there are some models that contain both a barometric sensor and a hygrometer. This means you get two measurements at once!

Weather Station Types

There are three main types of weather stations available today. Each has its own advantages and disadvantages. All these devices work by measuring one or more parameters within their environment. There are four basic categorie s of weather stations; Barometers, Hygrometers, Thermometers and Humidity Sensors. A fifth category would be Rain Gauges. However, this article will focus only on the first three categories.

Barometrics - Pressure Sensing Devices

The simplest form of weather station is the barometric device. In fact it is probably the oldest form of weather station still being manufactured today. These devices consist of a sealed container where air pressure changes due to variations in atmospheric conditions. 

Inside the container is a sensitive mechanism called a "barometer" which detects any change in pressure inside the chamber. When the outside atmosphere becomes too cold or dry, the pressure drops causing the liquid contained in the barometer to expand. 

As the pressure increases again, so does the volume of the liquid. By comparing the difference between the initial reading and final reading, we can determine how much water vapor was present in the surrounding atmosphere. If the amount of moisture is high then the relative humidity is low. Conversely if the amount of moisture is low then the relative humidity is high.

The advantage of using a barometer is that it requires no power source. Therefore it works well outdoors without needing batteries. Also because it uses a simple mechanical system, it is easy to build and maintain. On the downside however, it cannot detect precipitation directly. Instead it must rely upon indirect methods such as observing cloud cover or detecting rainfall through a separate rain gauge. 

Another disadvantage is that it cannot accurately measure absolute pressures below about 10 mb. Below this level, the effect of gravity causes the column of mercury to rise slightly above zero degrees Celsius. Thus readings taken near sea level may show temperatures higher than expected.

 

Hygrometries - Moisture Sensing Devices

Another popular method of determining atmospheric conditions is to measure the amount of moisture in the air. The most common way of doing this is with an electronic hygroscope. An electronic hygroscope consists of a glass tube containing a solution of salt crystals. 

Salt solutions absorb moisture very quickly when exposed to humid air. So when moist air enters the tube, the crystal solution absorbs the moisture and expands. This expansion pushes up against a spring loaded piston. Once the piston reaches full extension, it triggers a switch which turns on an alarm circuit. At this point the user knows they have entered into a period of heavy dew formation.

A major drawback of this type of weather instrument is that it needs constant maintenance. It also tends to drift over time. To compensate for this problem manufacturers often include a calibration feature. They do this by adding a known quantity of water to the solution before each use. Then after every measurement, the user compares the new reading to the old one. Any differences indicate that the unit has drifted out of calibration.

 

Thermistors - Temperature Sensing Devices

Temperature sensing instruments are used to monitor temperature trends. Unlike other forms of monitoring, thermistors require electricity to operate. Their primary function is to sense heat energy emitted by objects like people, animals or machinery. 

Most thermistors are made of semi conductive material. Semiconductor materials conduct electrical current better under certain conditions. One condition is when electrons move freely across the surface of the material. When there is free movement of electrons, the material becomes hot. 

A second condition is when the material is heated from within. In these cases, the resistance increases due to increased electron mobility. Thermometer's can be placed inside a sealed container so that only heat escapes. As long as the outside environment remains at room temperature, the internal temperature will remain steady. However once the external temperature rises, the internal temperature begins to increase until equilibrium is reached.

 

Temperature sensors come in two basic types: 

1. Resistive 

2. Capacitive. 

Resistive devices consist of wires wound around a ceramic core. Capacitance devices work much like a capacitor except instead of having metal plates separated by insulating material, they contain a dielectric layer between two electrodes. Both types of sensor respond differently to changes in ambient temperature. 

For example, a resistor experiences a change in voltage proportional to its own temperature. But a capacitor does not experience any direct relationship between voltage and temperature. Rather, it responds more strongly to changes in pressure. Because of their different responses to temperature variations, both types of device can be combined to form multi-function units. These combine the functions of both types of sensor.