Do-it-yourself air humidity meter: instructions for assembling a hygrometer

Sensors for solid media according to the principle of operation

As we have already said, some humidity and air temperature sensors are universal: they can work in soil or loose mixtures.There are also specialized devices for solving such problems. Actually, there are not so many technologies for measuring the moisture content in granular media (soil, dry mixes, etc.).

Resistive sensors

These detectors operate on the principle of ammeters: the measuring medium acts as a resistor in the circuit. The soil or dry mixture, depending on the saturation with water, changes the electrical conductivity (or resistance). Accordingly, the strength of the flowing current also changes. Such sensors can only be electronic, since mechanical measurement of humidity in a solid medium is costly and impractical.

Two (or more, to improve accuracy) electrodes are immersed in the measurement medium.

The control module applies a small voltage to the contacts and measures the value of the electric current. The more moisture, the stronger the electric current. Reliable and fairly accurate design, not without flaws. First, the electrodes must be made of a material that is resistant to corrosion and mechanical damage. Secondly, when calibrating the instrument, the salt content of the soil (or material) must be taken into account.

Capacitive soil moisture sensors

Perhaps the most popular devices among apartment "farmers". Today it has become fashionable to grow some food not in the garden, but, for example, in an apartment in Moscow. To ensure a good harvest, electronically controlled intensive farming technologies are used. The controller receives information about temperature, humidity and light levels, and simulates the natural conditions for your garden bed on the windowsill.

If the control system is fine-tuned, there is no need to monitor the plant growth process on a daily basis.It is enough to replenish the container for irrigation, and harvest in a timely manner.

The advantage of such a device is the ability to work "on the machine". In addition, such a sensor can be made by hand.

How does a hygrometer work?

There are several types of hygrometers, each of which is based on its own principle of operation:

• Hairline;
• Film;
• weight;
• Ceramic;
• Condensing;
• Electric.

The easiest to understand is hair:

1. The basis of the mechanism of action is devoid of fat hair;
2. Under the influence of the level of humidity, the length of the hair itself changes;
3. You can record changes from 30 to 100% humidity;
4. The device is easy to manufacture and cheap.

Weight works a little differently:

• Consists of a system of tubes filled with a special substance;
• The content is able to absorb moisture from the surrounding air;
• With the help of a pump, air is "stretched" through the tubes;
• Weighing the filler before and after, determine the moisture content.

Electronic hygrometers can use chilled mirrors, capacitors and salts. But the end result is always displayed on the screen as a pair of numbers.

The mechanism of operation of each apparatus boils down to the fact that a system is created that in one way or another reacts to air humidity. The changes taking place in this system are fixed, and the final result is issued. The only question is accuracy, durability and cheapness. Which device will be the most optimal in all three parameters.

Hygrometers are of the following types:

• hairline;
• weight;
• ceramic;
• condensation;
• electronic;
• psychrometric (psychrometer).

Let us consider in more detail the technology of operation of each type of device.

Hair hygrometer

Hair hygrometers work on the basis of normal hair and its properties. Hair can change its length at different humidity levels. It is stretched on a plate or frame and, lengthening or shortening, moves the arrow, which in turn moves along the scale of the device.

Read also: Features of cassette keeping of bees in the Berendey pavilions

A hair hygrometer is good for home use if you don't need to get extremely accurate data.

Also, they should not be moved or mechanically acted upon in any other way. At the slightest impact, the hygrometer can fail, since its entire design is quite fragile and delicate.

Weight hygrometer

An absolute weight hygrometer consists of several tubes brought into the system. They contain a hygroscopic substance that can absorb moisture from the air.

A certain portion of air is drawn through the entire system, taken at one point in space.

So, a person determines the mass of the tube system before and after passing air through it, as well as directly the volume of air carried out and, with simple mathematical manipulations, can calculate the studied indicator in absolute terms.

Mechanical (ceramic) hygrometer

A porous or solid ceramic mass, which also includes metal elements, has electrical resistance. Its level is directly dependent on humidity.

For its correct action, the ceramic mass must consist of some metal oxides. Kaolin, silicon and clay are used as the basis.

Condensation hygrometer

This hygrometer is quite easy to use. The principle of its operation is based on the use of a built-in mirror.The temperature of this mirror changes along with the temperature of the air in the surrounding space.

Its temperature is determined at the initial moment of measurement. Further, drops of moisture or small ice crystals appear on the surface of the mirror. The temperature is measured again.

With the help of the temperature difference determined by the condensation hygrometer, the humidity of the air is determined.

Electronic hygrometer

A layer of lithium chloride is applied to a plate of glass or other similar electrically insulating material.

Humidity changes - the concentration and resistance of lithium chloride increases or decreases.

It is worth noting that the readings of an electronic (electrolytic) hygrometer can be slightly affected by air temperature, so it is often equipped with a built-in thermometer.

Such a hygrometer is extremely accurate and gives readings with a minimum error.

Psychrometric hygrometer (psychrometer)

The psychrometer is a system of two conventional alcohol thermometers. One of them is dry, and the second is wet (this state is regularly maintained).

The faster the moisture evaporates, the lower the relative humidity. The condensed liquid then begins to cool. Thus, the difference between the temperatures of two thermometers and the rate of evaporation are established, and on their basis the humidity of the air is found.

The psychrometer is not a hygrometer in the literal sense, but it measures the same indicator, so they are often identified.

In fact, the principle of operation of any hygrometer is quite simple and is based on the physical or chemical properties of materials and substances.

Almost any hygrometer is suitable for use in your home, but the most accurate data is still given by electronic hygrometers.

Using a hygrometer in an incubator

It should be remembered that with a hygrometer installed in the incubator, opening the case cover leads to a rapid drop in the humidity stored there, and the previous readings of the device will be restored only within an hour.

For successful operation of the device for many years, it is necessary to follow the recommendations of the manufacturer:

• the moisture meter should be protected from bumps and falls, as well as mechanical damage to the wire and sensor;
• exclude exposure to direct sunlight and being in a draft;
• observe the recommended temperature regime for the normal functioning of the moisture meter (-40 ... + 70 ° С);
• Avoid direct contact with moisture and contamination of the device.

How to make your own humidity sensor

With a circuit based on a single transistor, a simple humidity sensor can be made. A plate with a sensor that will warn of an increase in humidity levels. It is made from trimmed fiberglass. The area is divided into two sectors and well tinned.

The essence of the robots: humidity falls on the contact of the klinger, they form a rebuff and detect a device that amplifies the electrical oscillation. And electrically charged particles run through the device.

For robots, an LED kliger and a piezo emitter with a paradigm, a relay winding are suitable. Its contacts will serve as the initiator or circuit breaker of the electrics.

The sensitivity of the device reacts with a construction resistor that reacts to any level of passing current.

Popular types of appliances

The procedure and features of measuring the level of humidity with a hygrometer depend on the type of laboratory equipment used. Such devices differ from each other in the device, principle of operation and a number of other parameters.

By design, hygrometers are mechanical and electronic. The former have a dial with an arrow, the latter have a display on which information is displayed.

According to the principle of operation, there are such types of devices:

• film;
• hair;
• weight;
• capacitive;
• resistive;
• ceramic;
• condensation;
• electrolytic;
• psychometric.

Film hygroscopes have a dial with an arrow. The sensor is a special film. It consists of organic material and is connected to the arrow.

Under the influence of atmospheric humidity difference, the film changes its size. This leads to the fact that the arrow is shifted to the right or left side, showing the result on the dial.

The advantage of the hair hygrometer is its simple design. This device can be used to determine the humidity of the air at temperatures below zero degrees.

The main element of hair appliances is skimmed human or synthetic hair stretched over a frame with an arrow. The principle of operation of the device is similar to film types of hygrometers.

When the humidity changes, the length of the hair changes. This causes the arrow to deviate in a certain direction.

Weight hygroscopes are used to calculate absolute humidity. They are equipped with tubes with hygroscopic material. When passing through the air mass, the filler absorbs moisture and increases in weight.

Sampling is carried out by a special pump. The system is weighed before and after air injection. Absolute humidity is calculated based on the obtained indicators, the volume of air mass passed through.

Capacitive hygrometers incorporate an oxide capacitor. Its capacity varies depending on the concentration of moisture in the air. Such models must be periodically calibrated. This is due to the fact that over time the capacitance of the detector decreases, which affects the measurement accuracy.

Resistive hygroscopes work on the principle of changing the level of humidity depending on the electrical resistance of salts and polymers. Ceramic devices consist of a dial with an arrow. The sensor is a special ceramic mixture (clay, silicon). Its electrolytic resistance depends on the level of humidity.

Ceramic hygrometers only show the level of humidity. They don't have any additional features. But they are accurate and allow you to monitor changes in the microclimate in the room.

Devices of the condensation type are also called Lambrecht hygrometers. The principle of operation of the equipment is based on the use of a built-in mirror. The temperature of this element changes with the temperature of the atmospheric air.

The main element of electrolytic devices is a glass, polystyrene or other insulating plate coated with an electrolyte layer. Depending on the concentration of moisture in the air, the resistance of the electrolyte changes.

The condensation hygrometer is highly accurate. But for domestic use, it is not suitable due to certain difficulties of use.

Psychometric hygrometers measure the humidity of atmospheric air based on the decrease in the temperature of the wetted body. They consist of two thermometers: dry and humidified.

The device is also equipped with a feeder - a glass flask that is filled with water. The calculation is carried out by the researcher independently. It helps to determine the relative humidity of the air with a hygrometer table attached to the device.

In addition to instruments, there are alternative ways to measure humidity. More details - read on.

Types of hygrometers for an incubator

Moisture meters can be of different types. Depending on the principle of their work, each of them has its own characteristics, certain advantages and disadvantages.

weight

The operation of this device is based on a system of tubes interconnected. They are filled with a hygroscopic substance that absorbs air. Absolute humidity can be calculated from the difference in weight before and after passing a certain portion of air. For this, a special formula is used.

The disadvantage of this device is obvious - it is quite difficult for an ordinary user to carry out the necessary mathematical calculations every time. The advantage of a weight moisture meter lies in the high accuracy of its measurements.

Hair

This type of device is based on the property of the hair to change length with changes in humidity. To determine this indicator, in the container of the incubator, the hair is pulled over a special metal frame.

Did you know? You can check the health of the moisture meter upon purchase by holding the device in your palm for a few seconds. Under the influence of the heat of the human body, the readings of the sensor should change.

Film

The principle of operation of this device is based on the property of an organic film to stretch at high humidity and shrink when its level decreases. The film sensor works on the principle of a hair sensor, only here changes in the elasticity of the film under the action of the load are recorded.

We advise you to read about how to choose a thermostat for an incubator.

The data is displayed on a special board. The pros and cons of this method are identical to the characteristics of the hair moisture meter.

Ceramic

The operation of this device is based on the dependence of the resistance of a ceramic part, which consists of clay, kaolin, silicon and oxides of certain metals, on air humidity.

Important! To increase the humidity in the incubator, the eggs are sprayed with water. However, this should only be done with waterfowl eggs.

How to choose a hygrometer

To choose the right hygrometer, decide how it will be used. In everyday life, preference is given to inexpensive mechanical hygrometers, while in production, mainly electronic of various types are used, because they give the highest measurement accuracy.

It is important to decide what the device will be used for in the first place and how often measurements will be taken. For use in construction, a specialized hygrometer may be needed for a specific group of materials, such as wood, and in other cases, the standard model will be suitable.

Decide what you want to measure and evaluate the capabilities of the various hygrometers on the market.

The conditions of use are also a significant factor.

Pay attention to the range of temperature and humidity in which the device will give correct readings.Depending on the nature of the production, you may need a hygrometer that operates at extremely high or extremely low temperatures.

You should also take into account the error of changes.

It also matters how the data will be processed in the future. In the simplest case, you just need to take measurements once to estimate the humidity in the room or the micro-humidity of the gas mixture. But stationary hygrometers allow you to solve more complex problems. With their help, you can track the change in parameters, signal the achievement of threshold values, and therefore more effectively control the process.

Do not forget about the ergonomic characteristics of the device. Large numbers on the display should be high contrast and easy to read. You may prefer to purchase a model with a backlight so that you can easily read readings in any light level. Ergonomics is especially important for portable devices: their body must be light, so that it is comfortable to hold in your hand.

Is it possible to do without devices?

"Folk" methods for assessing air humidity

If we talk about the complete absence of instruments, then, yes, there are a couple of methods, however, a very approximate assessment of the relative humidity of the air.

Use for these purposes an ordinary candle. To conduct the "experiment" it is necessary to completely eliminate the draft in the room, that is, close all windows and doors. It is desirable to achieve the maximum possible darkness.

The flame of a candle can indicate excessive humidity in the air.

After the candle is lit, watch its flame.

- An even vertical flame with a yellow-orange tongue and clear boundaries indicates a normal level of humidity.

- If the flame "plays", and the areola around the tongue takes on a crimson color, one can assume excessive humidity.

And that is all…

The second way is using a glass of chilled water.

For the experiment, you need to collect a glass of ordinary tap water and place it in the refrigerator for several hours. It is required that the water cools down to about 5÷6 degrees.

Experience with a glass of water

After that, the glass is taken out, placed on the table in the room where the humidity study is being carried out. You should immediately visually evaluate the condensate that appeared on its walls after being transferred from the refrigerator.

It is important that the glass is no closer than 1 meter from windows, walls and heaters. In this position, avoiding a draft, it is left for about 10 minutes.

After that, an evaluation can be carried out.

- If the condensate on the outer walls is dry, this indicates insufficient air humidity.

- The condensate, in principle, has not undergone any special changes - the humidity can be considered within the normal range.

- The condensate collected in drops and even dripped onto the surface of the table - the humidity in the room is clearly increased.

Again, there is no need to talk about accuracy. And the preparation for the experiment, which requires several hours, is also not attractive.

But in general, without devices, otherwise it will not work.

Homemade psychrometer from an ordinary home thermometer

Well, if you have the most common glass alcohol or mercury thermometer at your disposal, then humidity can be determined with an accuracy no less than that of professional instruments.

With a conventional thermometer it is fashionable to obtain a very accurate value of relative humidity.

To begin with, you need to put the thermometer in the room where the humidity determination is carried out, so that direct sunlight does not fall on it. Best of all - on a table in a shaded place closer to the center of the room. Naturally, the draft must be excluded. After 5÷10 minutes, temperature readings in the room are taken and recorded.

After that, the thermometer flask is wrapped with a richly moistened cloth (room temperature!), And put in the same place. After 10 minutes, readings are taken, as for a “wet” thermometer in a psychrometer. Record them too.

Having two thermometer readings on hand, for “dry” and “wet”, you can find the psychrometric table, go into it and determine the level of relative humidity. And even better - to conduct a more thorough calculation.

Do not be alarmed, the author is not going to "load" you with formulas. All of them are already included in the online calculator offered to your attention.

The calculation algorithm was compiled for the normal movement of air in a house or apartment, which is characteristic of the normal operation of natural ventilation.

The calculator asks for another value - the level of atmospheric pressure in millimeters of mercury. If it is possible to specify it (there is a barometer at home or there is information from a local weather station) - excellent, the results will be as accurate as possible. If not, well, then yes, leave normal pressure, the default is 755 mmHg. Art., and the calculation will be carried out from it.

This calculator should not cause more questions.

Psychrometer - device, principle of operation

Humidity in the apartment is one of the main indicators of the home microclimate. Too much or too little moisture in the air can cause discomfort and negatively affect your well-being.

Humidity is a measure of the amount of water vapor in the air. Humidity at home varies depending on weather conditions and human life processes.

Without special equipment, it is difficult to determine the relative exact level of air humidity. However, the concentration of moisture that does not correspond to the norm can be determined by dryness of the skin and mucous membranes or the accumulation of condensate (dew point) on windows and mirror surfaces.

Relative humidity is the content of water vapor in the air and its interaction with air temperature.

A device for measuring air humidity is called a hygrometer.

There are several types of hygrometer:

• hair,
• film,
• weight,
• condensation,
• psychrometric,
• electronic.

Psychrometric hygrometer

The psychrometer is based on the interaction between "dry" and "wet" thermometers. The device has two thermometers with tinted liquids (red and blue). One of these tubes is wrapped in cotton cloth, the end of which is immersed in a reservoir of solution. The fabric gets wet, and then the moisture begins to evaporate, thereby cooling the "wet" thermometer. The lower the humidity in the room, the lower the thermometer reading will be.

To calculate the percentage of air humidity on a psychrometer, you should find the value of air temperature in the table on the device according to the readings of the thermometer and find the difference in values ​​at the intersection of the indicators.

There are several types of psychrometers:

• stationary. Includes two thermometers (dry and wet). Works according to the principle described above. The percentage of air humidity is calculated according to the table.
• aspiration.It differs from a stationary one only in the presence of a special fan, which serves to blow the thermometers with an incoming air stream, thereby speeding up the process of measuring air humidity.
• remote. This psychrometer is of two types: manometric and electrical. Instead of mercury or alcohol thermometers, it has silicon sensors. However, as in the first two cases, one of the sensors remains dry, the second remains wet.

The operation of the psychrometer is based on the degree of cooling by evaporation of the "wet" thermometer reservoir with a balance of heat transfer and a constant speed depending on the amount of moisture in the ventilated air stream.

Relative humidity is determined from the temperature of the "wetted" thermometer and the air temperature.

The psychrometer consists of two main parts - head 1 and thermal holder 3 (Fig. 1).

Inside the head there is an aspiration device, consisting of a winding mechanism, key 2 and a fan for the MV-4-2M psychrometer; the M-34-M psychrometer uses an electric motor with a fan, connected to an alternating current network with a voltage of 220 V.

Thermometers 4 are installed on the thermoholder 3, one of which is “wetted”, and the other is used to measure the air temperature.

Thermometers are protected from the effects of solar radiation both from the side - by slats 5, and from below - by tubes 6.

At the bottom of the thermoholder there is a device for regulating the aspiration rate. It consists of a cone-shaped valve 8 and a spring-loaded screw 7. When the screw is turned, a certain part of the section of the tube 9 is blocked, which leads to a change in the aspiration rate.

Speed ​​adjustment to the set value is carried out at the factory and, if necessary, at the verification office.

Rice. 1. Scheme of aspiration psychrometer MV-4-2M

When the fan rotates, air is sucked into the device, which flows around the tanks of thermometers, passes through the tube 9 to the fan and is thrown out through the slots in the aspiration head. The psychrometer is supplied with: a wetting pipette consisting of a glass tube inserted into a rubber balloon with a clamp; shield (wind protection) to protect the aspirator from the influence of wind; a metal hook for hanging the device by the ball on the aspiration head, calibration certificates for thermometers and a passport. To calculate humidity according to thermometer readings, psychrometric tables are used or calculated using a formula. Formulas and auxiliary tables for calculating absolute and relative humidity are presented in Appendix 1

Classification of instruments for measuring relative humidity (hygrometers)

The state of human health depends on a large number of factors. An important role in this is assigned to the purity and humidity of the air. If there is not enough moisture in the room, the mucous membranes of the respiratory tract will dry out, as a result of which a person may develop diseases associated with the vital activity of harmful bacteria.

Hygrometer with electronic display

The simplest hygrometers involve the use of a table of relative air humidity; by the temperature indicated in it, one can get an idea of ​​the state of the microclimate at the current moment. In more advanced models, there is a set of chips that independently perform calculations and display the result on the screen electronically.

In addition to traditional designs, the offer of the modern market allows you to buy moisture meters with additional functionality. Such devices display other data on the screen:

• air temperature in the room;
• current time and date;
• atmospheric pressure level.

The most used types of instruments for measuring air humidity

Features of the hair indoor air humidity meter

This type of device is used to determine the humidity index within 30-80%. The design of the device consists of several elements:

• metal frame in the form of a frame;
• measuring scale (the step of each division corresponds to 1% humidity);
• human hair (defatted);
• arrow adjustable with a screw;
• a pulley designed so that you can throw the free end of the hair with a fixed weight.

Modern devices for measuring air humidity can also show the date

A hair hygrometer is a type of measuring instrument designed to determine air humidity, the principle of which is based on the hygroscopicity of a human hair, in other words, the ability to lengthen or shorten under the influence of moisture. When the humidity in the room decreases or increases, the tension of the hair is weakened or vice versa, it increases. As a result of this, the pulley turns and sets in motion an arrow pointing to the scale. Due to this, it is possible to determine the exact indicator of the humidity of the environment.

The hair type hygrometer has a significant advantage over other devices. Its readings cannot be affected by air temperature, as is the case with electrolytic models.It does not require electricity for its operation, the hygrometer functions due to mechanical processes.

What instrument measures humidity in absolute terms?

In order to identify the current level of humidity in a room, two values ​​should be known: the relative humidity and the absolute value. The percentage ratio between them is the desired parameter. Therefore, it would be useful to know the name of the device for measuring air humidity in its absolute value and the principle of its operation. A weight hygrometer measures the amount of water vapor contained in one unit of air (in 1 m³).

Hygrometer mechanical type

The device includes several U-shaped tubes forming a system. Inside them is a hygroscopic substance that absorbs moisture from the air masses. A certain volume of air passes through the system, which is taken from one point. This design allows you to determine the mass inlet air and output, as well as its volume. The absolute value is determined by mathematical calculations.

Characteristics of ceramic devices for determining air humidity

Ceramic devices are a commonly used variety of moisture meters, this type of moisture meters are simple and mechanical. The device is made of ceramic mass, which can be porous or solid. It contains metallic elements. The ceramic mass has electrical resistance, and the humidity of the room has a direct effect on the level of this resistance.

Room hygrometer

In order for the mechanical design of the indoor air humidity tester to function properly, certain metal oxides must be incorporated into the ceramic body. Silicon, clay and kaolin are used as a base.

When should a hygrometer be installed?

Experts recommend maintaining the humidity in the premises as strictly as the temperature. This is due to several factors:

• From too humid environment, colds quickly spread, fungi and mold appear on building structures.
• A dry atmosphere is also unhealthy. Dried mucous membranes in the throat and nasopharynx quickly lose their protective properties.
• With an excess of moisture in the pantry, vegetables begin to rot, and with a lack of it, they wither and become inedible.

Construction, food industry and medicine, utilities and greenhouses, enterprises, schools and preschool institutions need to maintain constant humidity. Knowing and controlling its indicator in a given range, you can improve all areas of your existence (including health and material well-being).

How to choose?

Various moisture analyzers are usually chosen by engineers and other professionals who clearly understand what they need. For the home, you can limit yourself to the simplest hygrometer. But not everything is so simple. Be sure to take into account, for example, the design features of each device so that it fits into the interior. Psychrometric models are best left to professional meteorologists—they are fairly accurate but difficult to handle.

Since air humidity drops sharply in winter, it is very important to focus on a measurement range of 20-70% at least.For garages, basements, baths, saunas, bathrooms and greenhouses, it is better to choose models that can measure humidity up to 100%

You don't have to skimp when buying. In domestic conditions, an error of 2-3% is quite enough. In the children's room, it is advised to put models resembling toys.

Summing up

Both the lack and excess of water vapor in the atmosphere adversely affect the general condition and health of people. Especially often such problems arise in a city apartment. They can be completely eliminated with the help of special humidifiers or dehumidifiers. However, in order not to make the situation worse, you should first find out the level of moisture content. Here comes to the aid of a device for measuring humidity, which is called a hygrometer.

There are two types of hygrometers: mechanical and digital. The former are not as accurate, but they are cheap and reliable. The latter are convenient in that they have several functions at the same time, but they are more expensive and not so reliable. Nevertheless, among both types of device, you can choose a high-quality, accurate and inexpensive model.

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