People who regularly watch the weather news on television are familiar with the term relative humidity. They understand that higher humidity numbers mean less comfort in the warm months. Scientists have many more reasons to track humidity beyond simple comfort. For engineers, scientists and weather reporters, humidity sensors provide the information. This short piece will introduce the types of measurement and sensors used.
The starting point of any discussion of humidity is a definition. Air or any gas can hold an amount of water vapor. This vapor content in a gas is humidity and is not visible. Visible forms of water (steam, fog, snowflakes) are condensing from vapor to liquid. There are three basic measurements of humidity. Each different type uses different measurement techniques and is reported in specific units of measurement. The ranges of these measuring systems overlap and allow mathematical conversion between units of measure.
The most common humidity measurements are dew point, relative humidity, and relative humidity. Each of these is best suited for specific applications where the range and accuracy of the measured values is used in research or process control. Humidity measurement has advanced along with other technologies and is a common part daily life.
The "bad hair day" is caused by the way human hair responds to humidity. Early scientists took note of this effect and built the first relative humidity instruments around it. Horse hair was also used in some indicators and chart recorders. With the invention of synthetic materials like nylon, hair-based instruments became obsolete. Synthetic fibers have more predictable responses and are more easily calibrated. The invention of transistors and solid-state electronics led to modern sensors that are tiny, relatively inexpensive and much more robust.
Many weather reports include a dew point reading. This is the temperature at which the water vapor in air begins to condense into liquid. Dew point figures are very important in some manufacturing processes such as painting or anything that uses compressed air. Dew points were originally measured using chilled mirror technology. This could be limited to a certain range of temperatures and calibration was unstable. Modern solid-state dew point sensors are accurate down to -40degrees F. And are much more dependable.
The most precise humidity measurement is absolute humidity. This is the measurement of the weight or mass of water vapor in a specified volume of gas. The unit of measurement is grams per cubic meter or grains per cubic foot. Absolute humidity is useful in most engineering or scientific applications where the values are used in calculations. Today's sensors can measure absolute humidity in polluted environments up to 200degrees C.
In manufacturing, changes in humidity can impact the stability of processes. This is particularly true with painting. Constant real-time monitoring of humidity allows automatic adjustments to the process to compensate for changes. Research results can be skewed by changes in humidity so recording humidity during the research is important. Modern sensor manufacturers have products to cover almost any application.
Some internet research can find humidity sensors to meet almost any requirement. Today's sensors are accurate, tiny, relatively inexpensive and much more durable than the early horse-hair based indicators. And you will not need to rely on a weatherman.
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Our qualified technicians have over 30 years of experience in providing instrument calibration services and full service repair. We provide a wide range innovative technical solutions, including data loggers, humidity sensor, and pressure transducer.
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