Your thermometer is probably wrong
Thermometers surround us everyday. They're in our cars, outside our banks, sitting on our decks and even on our phones. But not all are created equal and not all locations give accurate readings. This means that the temperature you see might not be accurate and, in fact, it might be far from it.
For starters, placement counts. Things like sunlight, radiant heat or precipitation can all affect the reading. Then there is the type of instrument. Some aren’t even thermometers.
The most common way of measuring temperature in our day-to-day lives is a thermistor. A thermistor is a device used to measure temperature through resistance in an electrical circuit. By measuring the resistance over a change in material, the temperature can be deduced using a rather simple math equation.
Thermistors can be very accurate at given temperature ranges based on materials and the desired ranges. The downside of thermistors is that they are very susceptible to environmental factors.
Cars aren’t necessarily known for accurate temperature readings, but for many it’s the reading seen most often. The inaccurate reading comes from a few different factors.
The thermometer in your car isn’t even a thermometer. It’s a thermistor. And like many other applications, the placement of the thermistor has a direct impact on the temperature reading.
The thermistor that gives the outside temperature reading in your car is typically placed inside the front bumper. This means that instead of an ambient air temperature you often wind up with the localized temperature at the front of your car.
Things like sunlight, radiation from the ground, moisture, and even speed can change the exact reading of resistance on the thermistor. That means the reading of temperature you see in your car might not be pinpoint accurate.
The bottom line: use you car’s temperature reading as a general reading. It’s a good way to tell if it's hot or cold, or even if temps are rapidly changing. What it might not work for is knowing the exact temperature when it comes to the difference between ice and water on the roads.
The thermometer on your deck faces similar woes. The accuracy can be greatly impacted based on location and placement alone. Temperature, as observations are concerned, is a reading of ambient air sheltered from outside influences to limit the effects of nearby elements.
Things like sunshine have a major influence on temperature reading. Sun shining directly on a thermometer can increase the reading by as much as 10 degrees.
The heat given off by your house can also influence the reading of the thermometer on your deck. For these reasons it is important to know how and where to place your temperature sensor for the most accurate reading.
There are three basic principles to keep in mind when placing a thermometer: sunlight, airflow and height.
Direct sunlight will increase the temperature reading of your thermometer. The best location will avoid direct sunlight all day long. If direct sunlight is impossible to avoid, you can always build an enclosure to block any direct light from hitting your thermometer.
This brings us to the next thing to keep in mind. Airflow is critical in making sure you are getting an accurate temperature reading. Good airflow means you won’t get any readings of stagnant air easily influenced by environmental surroundings.
The most common outside influencer is the ground. Radiation given off by the ground can influence the temperature reading if the thermometer is placed too low. The best way to avoid this is by making sure the thermometer is more than 6 feet off the ground.
Sunlight, airflow and height are the three things to remember when placing a thermometer. Be sure to avoid direct sunlight, have good airflow and keep the thermometer high off the ground.
Due to concerns of mercury poisoning, modern bulb thermometers are typically filled with alcohol. It works well to give a temperature range for most of the U.S. but here in Alaska, there is something to keep in mind. Alcohol freezes at 38 degrees below zero Farenheit. That means many locations around the state have seen the thermometer freeze in our recent cold snap.
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