Definition of humidity

A classic saying is that air humidity (abbreviated as humidity) is a physical quantity that represents the amount of water vapor and humidity in the air. The humidity referred to in daily life is often relative humidity, expressed as% RH (Relative Humidity), which is the percentage of the vapor pressure of water in a gas to its saturated vapor pressure. Its value shows how high the saturation of water vapor is. In most industries, humidity also refers to relative humidity.

Main classification of hygrometers

1. Electronic style

Determine gas humidity based on the relationship between the electrical properties of materials and changes in humidity in the air. There are mainly: ① Resistance type, which is made by using substances with good moisture absorption properties to adsorb water vapor and cause changes in resistance. However, due to the significant influence of temperature on resistance, its inherent temperature coefficient makes it unable to work in a wide temperature range. ② Capacitive, using moisture sensitive materials to change the dielectric constant after absorbing water and alter the capacitance value. Compared with resistive hygrometers, it has significant advantages: high sensitivity, low power consumption, and small temperature drift. Its excellent performance has received widespread attention from scientists. Due to its ease of integration with COMS technology and the convenience of miniaturization and integration, the majority of hygrometers currently available on the market are capacitive.

The main drawbacks of electronic hygrometers are:

a、 Accuracy and long-term stability issues

The accuracy of a humidity sensor should reach ± 2% to ± 5% RH. Without this level, it is difficult to use it as a measuring instrument. It is quite challenging for a humidity sensor to achieve an accuracy of ± 2% to ± 3% RH. Typically, the characteristics provided in the product documentation are measured at room temperature (20 ℃± 10 ℃) and in clean gas. In practical use, due to the influence of dust, oil stains, and harmful gases, aging and decreased accuracy will occur over time. The accuracy level of humidity sensors should be judged based on their long-term stability. Generally speaking, long-term stability and service life are the top issues affecting the quality of humidity sensors. Products with annual drift controlled at 1% RH level are rare, usually around ± 2% or even higher.

b、 Temperature coefficient problem of humidity sensor

Humidity sensitive components are not only sensitive to environmental humidity, but also to temperature. Their temperature coefficient is generally within the range of 0.2~0.8% RH/℃, and some humidity sensitive components have different temperature coefficients at different relative humidities. The temperature drift is nonlinear, which requires adding a temperature compensation formula to the circuit. The use of microcontroller software compensation or humidity sensors without temperature compensation cannot guarantee the accuracy of the entire temperature range. The linearization of the temperature drift curve of the humidity sensor directly affects the compensation effect. Nonlinear temperature drift often cannot be compensated for well. Only by using hardware temperature tracking compensation can the true compensation effect be obtained. The temperature range within which the humidity sensor operates is also an important parameter. Most humidity sensitive components are difficult to operate normally above 40 ℃.

c、 Interchangeability issues

At present, there is a common problem of poor interchangeability in humidity sensors. Sensors of the same model cannot be interchanged, which seriously affects their effectiveness and adds difficulties to maintenance and debugging. Some manufacturers have made various efforts in this regard, but the interchangeability is still poor, and have achieved good results.

b、 Application scenario issues

Electronic hygrometers cannot be used in situations that are highly sensitive to electronics or current, as they can easily cause explosions.

2. Hair hygrometer

The main proteins in hair come from a group of proteins called keratin, which belong to the same protein family that forms nails. The chemical bonds connecting keratin molecules endow hair with strength and flexibility, as well as predictive response to humidity. When the humidity increases, hair can relax and elongate, and then shrink again when the humidity decreases.The amount of water vapor it absorbs from the air increases with the increase of relative humidity, and the length of hair is related to the amount of water it contains. By utilizing this change, a hair hygrometer can be manufactured. Wash the hair with alcohol or other substances to remove oil, and place it in a container with ten strands of hair as a bundle. Using the lever principle, expand its elasticity and use the pointer to directly indicate the humidity on the scale plate. Another method is to fix one end of the hair and hang a small weight on the other end. In order to see the changes in hair length clearly, the hair is wrapped around a pulley and a long pointer is installed on the pulley. Due to the weight of the weight itself, the hair is tightly pressed onto the pulley. When the hair elongates, the pulley rotates clockwise and drives the pointer to deflect downwards along the arc, while when the hair shortens, the pointer rotates upwards. When the air is dry, the position pointed by the pointer is 0. When the water vapor in the air reaches saturation, the point pointed by the pointer is counted as 100, and then checked with a dry wet bulb hygrometer to mark the degree. This way, the relative humidity of the air can be directly measured.

for example Kailonda pointer hair thermometer and hygrometer

Product model: KTH-1

Kailonda pointer KTH-1 hair temperature and humidity meter and hair temperature and humidity meter are widely used in households, laboratories, animal husbandry, instrument workshops, libraries, hospitals, computer rooms, homes, hotels, restaurants, coal mines, oil mines, observatories, etc.