Instruments for measuring indoor air humidity hygrometers: how to measure and determine this indicator

Indoor air humidity is one of the most important indicators that determine the microclimate in the house. If the temperature and speed of air flows can be roughly determined by personal feelings, then say how much water in the volume of the room "by eye" will not work. How to determine the humidity of the air? For this, either a device for measuring air humidity in the room is used, or improvised means.

They all have individual accuracy and order of use.

Temperature measurement was discussed in a previous article.

Physical concept

Humidity is the content of water vapor in the air. The comfortable existence of living organisms, the possibility of the development of living nature, the preservation of materials is possible only at certain values of this parameter.

It happens:

absolute;
relative.

Absolute shows the amount of water vapor in a certain volume. Most often it is measured in g / m3. It has no practical value, since it is impossible to determine the normal humidity or not, knowing that the amount of water vapor is 10 g / m3.

The maximum values change depending on the air temperature. At -30 ° C this parameter is 0.29 g / m3, at 0 ° C - 4.8 g / m3, at + 30 ° C - 30.4 g / m3. The maximum value is reached at a temperature of 100 ° C (boiling point of water) and is equal to 598 g / m3.

The relative is determined by dividing the value of the current humidity by the maximum possible at a certain temperature, multiplied by 100. The humidity is measured in percent. It is widely used in weather forecasts, food composition, characteristics of industrial, warehouse and residential premises.

Moisturizing methods

In order to bring the humidity level in the room closer to the norm, you can do the following:

Try one or several variants of their proposed methods and strive for optimal indicators of air humidity in the apartment, because this is very important for your health.

Attention, only TODAY!

The important indicators that determine the microclimate of an apartment, house or any other room are temperature and moisture content in the air. And if the temperature can be roughly guessed by sensations, then for the second parameter you will need a special device to determine the humidity of the air.

If there are too many vapors in the air, or, conversely, little, this greatly affects immunity. To avoid health problems, special devices are used to measure humidity.
In this video you will learn what a psychrometer is.
Humidity is of two types:
Absolute
... Shows the amount of water in g / m2.
Relative
... To calculate its value, you need to divide the current humidity by the maximum possible, then multiply the resulting value by 100. Relative humidity is measured in percent. To get an accurate value, you need a device to determine the relative humidity of the air.

Flows through the windows

Excessive moisture in the air in the literal sense of the word deplorably affects the state of the objects around us. The inner surface of the windows is covered with drops of moisture, which flows down onto the windowsill. Bed linen, clothes, fur products acquire an unpleasant smell of dampness, they are inconvenient and unpleasant to use.

Food deteriorates, it is impossible to eat them. The enclosing structures and furnishings are moldy. Its spores spread through the air and can cause allergic reactions and a sharp decrease in immunity.A person is sick more often, the healing process takes longer.

Humidity and well-being

The humidity level is determined by the content of water vapor in the air. It can be absolute and relative. Our body is almost 70% water. To maintain the normal state of all vital processes in the body, it is necessary to consume at least 2 liters of clean water daily.

When a person is in a room with dry air for a long time, this negatively affects the condition of the skin, it ages quickly. During breathing, the lungs emit air, the humidity of which is 100%. When swallowing overdried, it is moistened due to fluids inside the body.
How to determine the humidity at home, you will see in this video:
A prolonged period in a room with dry air will dry out the mucous membranes. For this reason, people often experience the following symptoms:
dry mouth and dry lips;
nasal congestion;
sniffing;
slight coughing;
snoring at night.
Excessive moisture also has a detrimental effect on living organisms. Almost all objects in the living space are covered with drops and acquire an unpleasant damp odor. Such clothes and bedding are always unpleasant to use. Food products also deteriorate from excessive moisture, after which they are dangerous to use. All structures are gradually covered with mold, the spores of which spread everywhere. This often results in allergies and reduced immunity. Other more dangerous diseases arise if living conditions do not improve.
Excess moisture also adversely affects human health, causing mold and mildew.

Like in the desert

Lack of moisture in the air at low temperatures leads to hypothermia and dehydration due to increased sweating.

In such air, the level of static electricity increases, and the amount of dust increases. The mucous surfaces of the human body dry up. There is a sore throat, dryness in the nasal cavity, burning sensation in the eyes.

Increased moisture

The condensing hygrometer makes it possible to obtain the most accurate indicators that reflect the climatic comfort of the room. It is for this reason that many consumers will choose to buy this type of indoor air humidity meter.

The design of the device consists of the following elements:

metal box;
thermometer;
rubber bulb;
heat insulating pad;
front wall;
ring.

State-of-the-art instrument showing temperature, time and humidity
The condenser version of the moisture and temperature meter analyzes the amount of condensation that forms on the surface of the glass. A small beam of light is sent to a special mirror, which is cooled, as a result of which drops of water or ice crystals appear on the surface. An electronic thermometer built into the mirror determines the temperature. The device converts the received data into an indicator that displays the level of relative humidity.

The most optimal level of humidity in the room is 40-60%

The capabilities of an electronic device for measuring air humidity in a room allow you to measure changes in the concentration of electrolyte, which covers a material with electrical insulation properties. These materials include plastic and glass. Some device variants have an automatic heating function. They measure the dew point.

In addition, temperature fluctuations are taken into account, since it can affect the operation of the device, albeit insignificantly, therefore the devices are equipped with thermometers that facilitate their operation.

Electronic modifications are precise in measurements that mechanical designs cannot offer. The percentage of errors in their work is extremely low.

Hygrometer in modern design

Consumers can buy air humidity meters that have different specifics of work:

Measurement of air conductivity - devices determine the value of absolute humidity. To calculate the indicator of relative humidity, you need to measure the temperature.
Optoelectronic measurements - the instruments measure the dew point using a cooled mirror. It is frozen, after which the process of its gradual heating takes place.
Resistive measurements - the operation of the devices is based on the effect of changing the conductivity of polymers or salts under the influence of moisture levels.
Capacitive measurements - during operation, the unit monitors the change in the capacitance of a capacitor (polymer or metal oxide).

Psychrometric hygrometer VIT-1

Measurement of air humidity in the apartment is made so as not to face the difficulties of air dryness and increased moisture level. Some people think that this is not a particularly serious problem, so installing a hygrometer is pointless. But this attitude must be changed, since there will be negative consequences if the humidity level in the apartment is not controlled.

The relatively high level of moisture in the air at home is a source of microscopic fungi on surfaces. Also, such conditions are a favorable environment for the development of a fungus, which can adversely affect human health. Mold can lead to the development of allergies in a person.

But don't forget that allergies are just one of the diseases that mold can cause in humans. The fungus can become the source of a variety of infectious diseases.

Mold spores can end up in your food. A person and his entire body can begin to suffer from foodborne diseases. It is dangerous for all people who live in this house.

To avoid all these problems, it is necessary to regularly ventilate the room. Airing should take place regardless of the temperature outside the window and at any time of the year.

You will be able to enjoy a pleasant home environment due to the fact that moisture is always normal.

Measurement of indoor air humidity is carried out to avoid problems associated with dry air or high humidity. Perhaps many people think that this is not a valid reason to control humidity. In order to change the attitude towards this issue, one should pay more attention to the possible consequences.

Humid indoor air affects the development of mold. A humid environment is an ideal environment for the growth and proliferation of spores of this dangerous fungus. Mold spores flying in the air can lead to the development of various allergic diseases. Dampness in the room will allow the fungus to grow many times over and increase the number of spores thrown into the air.

Also, dangerous consequences can be caused by the ingestion of mold spores in food. This will lead to foodborne diseases, which tend to spread throughout the body. This poses a danger to all family members.

To avoid such dangerous consequences for the body, you should regularly ventilate the room. Despite the air temperature outside the window, it is imperative to carry out such events at least twice a day. This will help reduce the risks of humidification and mold to a minimum.

We use devices

The easiest way to measure air humidity is with a device. It is called a hygrometer. According to the principle of action, it happens:

by weight;
hair;
film;
electrolytic;
ceramic;
condensing;
electronic;
psychrometric.

In domestic conditions, psychrometric, hair, electronic hygrometers are used. To obtain reliable results, know how they measure air humidity.

The most reliable

Determination of air humidity using a psychrometer (from Greek - cold) is not difficult. The operation of the device is based on the fact that the presence of moisture lowers the temperature. The panel has 2 thermometers and a psychrometric table. The first thermometer is dry, the second is wet. To measure, you need to find the difference in temperature readings. In the table vertically the temperature of the air measured by the dry bulb thermometer is indicated, horizontally the difference in readings. The intersection of these two lines shows the relative humidity as a percentage.

The psychrometer is a reliable, fairly simple device for determining moisture content, giving accurate information. Requires constant monitoring for the presence of water in the wet bulb thermometer. Allows you to simultaneously monitor air temperature and humidity.

Simplest

The oldest and simplest moisture meter is the hair hygrometer. How to find out the humidity of the air using it?

It is enough just to look at the arrow, under which there is a scale with divisions in 1%. The principle of operation is based on a change in the linear dimensions of objects, depending on their saturation with moisture. Ordinary fat-free hair is used as such an item. Hence the name of the device "hair" came from.

As a disadvantage, a large measurement error (about 10%) can be noted. The advantages are:

high sensitivity;
quick response to changes in humidity;
large measurement range - from 30 to 100%.

It is used to determine the relative humidity of air in a residential area. It is often a beautifully decorated piece of furniture.

Most modern

How is humidity measured in modern classics and high-tech interiors? Modern design requires modern appliances. One of these is a digital (electronic) hygrometer. It is based on measuring the resistance of an electric current when the moisture content of the electrolyte changes.

Devices for measuring air humidity and the specificity of their application

There are many instruments for measuring moisture in the atmosphere. Even a pinecone can be called that word. The difference between them is only in what principle of action they use to determine. They can also be divided into electrical or mechanical.

Of those that can be purchased in the store, two are attracting attention:

hygrometer (there are many types);
psychrometer.

The main indicators when choosing a device for measuring humidity are the accuracy of the device and ease of use.

Hygrometer

Literally from Greek - a measure of moisture. Devices can measure both relative humidity (used in everyday life) and absolute. There are precise devices that measure the dew point. To obtain the last two values, a weighing hygrometer is taken. These indications are often needed for laboratory research and are not used at home.

The more moisture on the surface of the hair, the more the arrow deflects.

The simplest hygrometer is the hair and film sample. Its principle of operation is based on the fact that fat-free synthetic hair changes its tension when moisture enters it. The ends of the hair are rigidly fixed, one of them to the arrow on the scale of the device. An organic film can be used instead of synthetics. The devices measure moisture well in cold rooms (up to 0 ° C).

The condensation meter has a maximum operating range (from 0 to 100%!). Its principle of operation is that moisture settles on a flat mirror-like and cooled surface under the influence of a beam of light.A thermometer below the surface measures the reading by converting it to relative humidity. The device has large dimensions, so it is difficult to use it in an apartment.

We recommend: How to clean the multicooker inside and outside?

The ceramic moisture meter uses the electrical resistance of the mass. The substances contained in the ceramics are responsible for this. Kaolin and silicon have metal particles that change resistance when exposed to moisture. The device is compact and has gained wide popularity in home use.

Modern electric hygrometers measure for their readings:

in ambient air, electrical conductivity;
dew point by optoelectronic method;
resistance to salts and polymers;
capacitor capacity.

For work, microcircuits are used, which minimizes errors in accuracy and significantly speeds up the display of readings on the display.

It should be noted that it became possible to measure humidity using a smartphone. A special application is installed on the phone. The program determines the humidity in the room with good accuracy.

There is another type of hygrometer, which got its own name due to its high measurement accuracy and versatility.

Psychrometer

To check the humidity of the air, it uses one of the properties of the liquid - evaporation. The temperature difference is indicated by two thermometers. One of them is called dry. The second is wrapped in a damp cloth, one end of which is submerged in water.

The advantage of the device is that it guarantees accurate measurement of humidity in an apartment with deviations of 2-3%!

Evaporating, the liquid cools the wet thermometer. Therefore, the less moisture in the room, the lower the readings of this meter. Comparing the readings of both thermometers, using the formula, the absolute or relative humidity in the room is derived. And for simplicity, they use data from a ready-made table. At the intersection of the found temperatures, the desired humidity indicator is found.

There are three types of psychrometers:

The remote uses thermistors and thermocouples. They can be electrical or gauge.
The stationary one consists of two thermometers placed in a meteorological booth, one of which is wrapped in cambric.
The aspiration unit uses a special fan that blows the thermometers enclosed in a protective case.

The disadvantage is expressed in the impossibility of measuring at several points and the need for constant wetting, preferably with distilled water.

Yourself with a mustache

How to measure humidity if there is no device, and there is no need to buy it due to rare use? Come to the aid of ingenuity, the experience of generations, simple objects that are in every home.

Burn, burn my candle

Introducing the old-fashioned way to determine the humidity in a room. To do this, it is enough to make a moisture meter from a simple candle and a match. Before measuring humidity:

close the doors leading to adjacent rooms;
ensure there are no drafts;
light a candle;
watch the flames.

If the flame vibrates and the halo has a crimson color, there is a lot of water vapor in the air. If the combustion is exactly vertical and the flame is orange-yellow, the presence of water vapor is normal.

Water, glass, refrigerator

This method makes it possible to measure the humidity at home. This meter has only three moisture readings:

excessive;
normal;
insufficient.

Before checking the humidity in the apartment, pour plain tap cold water into a glass beaker. Refrigerate for 5-6 hours. The water temperature should be 6 ° C.

You can measure it either with an outdoor thermometer or a bathroom thermometer. Then place the glass on the table in the room, 1 meter away from windows and walls. After 10 minutes evaluate the result:

condensation on the outer walls of the glass has concentrated into drops that flow down onto the table - excess;
the physical state of the condensate has not changed - normal;
the condensate has evaporated or it has become much less - insufficient.

Optimum air humidity

We all know that the human body is 70% water. Therefore, it is vital for us that the air around us is not too dry. Otherwise, symptoms such as dry mouth, constant thirst, feeling tired, nasal congestion, snoring during sleep and coughing cannot be avoided. All these signs indicate that you need to increase the humidity in the room.
There are many ways to do this. But first, let's consider the simplest method of how to find out what is the humidity in your house right now. To do this, you need to take a glass glass, pour water into it and put it in the refrigerator. When the temperature of the water is the same as inside the refrigerator, the glass must be placed in the room. It is advisable to place it away from heaters and batteries.

If after 5-10 minutes the walls of the glass are dry, the humidity in the room is very low. If the condensation remains - medium, if moisture flows down the walls of the glass - the humidity is high. This is the so-called express method, but in order to know exactly what humidity you have at any moment, it is advisable to have a room air humidity meter at home.

He will reliably control the atmosphere of your home, showing in time what measures should be taken. If the humidity is 70-90% - the room can be ventilated, if 20-40% - be sure to humidify. After all, high humidity should also not be in the house all the time, this is fraught with the development of fungus and mold. The most optimal level of humidity, which must be maintained in the apartment, is 50-60%. If this threshold is exceeded, fungi may develop, and dust mites may appear. If the humidity is very low, it is fraught with bacteria, viruses, allergies and respiratory diseases.

Make a psychrometer yourself

An ordinary room mercury thermometer can be used to determine air humidity. With its help, it is possible to measure air humidity by a psychrometric method. Before measuring the humidity in the room, prepare an ordinary cloth and water.

The procedure for checking the presence of water vapor in the volume of air with your own hands is as follows:

measure the air temperature in the room and write it down;
wrap the mercury bulb of the thermometer with a damp cloth;
wait 10 minutes;
take and record the thermometer readings;
calculate the difference between dry and wet measurement;
download the psychrometric table;
find the humidity level in the room.

Such an air humidity meter does not take up much space, does not require additional costs, and provides the necessary measurement accuracy.

Overview of the hygrometer VIT-2: how to use, the main characteristics of the device

On the modern market, you can find a huge number of a wide variety of devices that differ from each other, both in functions and in design. Consider one of the simplest and most popular models of the device today, which is excellent for household use - the VIT-2 hygrometer, which can be bought almost everywhere.

The first feature of this particular device is that its use requires certain temperature conditions. So, in the cold season, the air temperature should not fall below -15 ° С, and in summer it should not exceed 40 ° С. Considering that we are talking about measuring humidity in rooms, it is not difficult to comply with this condition, but you still need to know about it.

Ambient temperature, ° C	Measurement range of relative humidity,%
20-23	54-90
23-26	40-90
26-40	20-90

The scale division of this hygrometer is 0.2 ° C, which makes it possible to obtain fairly accurate readings. And toluene is used as a thermometric liquid in this device, which, unlike mercury, is safe.

In order to understand how to use the VIT-2 psychrometric hygrometer, you need to have an idea of its appearance, as well as the principle of operation. Visually, it is a plastic base 290 mm high, 120 mm wide and 50 mm thick. On this basis, two thermometers are fixed, as well as a temperature scale and a psychrometric table. In addition, a glass feeder is also fixed there, which is necessary for humidifying one of the thermometers.

Room hygrometers VIT-1 and VIT-2

As mentioned, one of the thermometers receives data while remaining dry, while the other is constantly exposed to moisture. This is due to the fact that the capillary of this thermometer is in a special fabric material that perfectly absorbs water and, due to this, constantly maintains the required level of humidity. With this cooling, the readings of the second thermometer are different, which makes it possible to compare the data.

In order to make the necessary calculations, it is enough to use the table. Having found the obtained indicators of "dry" and "wet" thermometers, at the point of intersection of these values, the relative humidity of the air will be indicated.

Another important condition for the accurate operation of such a device is that the speed of movement of air flows in the room should not exceed 1 m / s. Otherwise, the difference between the readings of the thermometers will be greater than it actually is, and as a result, you will get an incredibly underestimated air humidity.

Psychrometric hygrometer device

Normal indicators

It is not enough to determine the humidity in the room. It is also necessary to know whether the received data is normal. The optimal and most comfortable value is 45%. At the same time, the acceptable range of variation of air humidity in the apartment is 30 - 60%. It is recommended to maintain a different amount of water vapor in rooms with different functional purposes:

hall, dining room, living room, kitchen, bathroom - 40-60%;
bedroom for adults and teenagers - 40-50%;
children's room - 45-60%;
cabinet - library - 30-40%.

It is quite troublesome to achieve different indicators of the presence of moisture, even in small rooms. First of all, it is necessary to ensure the rate of humidity. In most modern living quarters, it is not enough due to the large number of heating and electrical appliances.

From this, the state of health worsens, the efficiency decreases. Children suffer the most from this.

The principle of operation and types of devices

Hygrometers are based on variations in the physical parameters of different materials. When the amount of vapors in the air changes, the properties change: density, weight, length and other working parameters of substances. By registering changes in the physical characteristics of materials, one can draw conclusions about the amount of vapors in the air.

Hair and film moisture meters

The simplest mechanisms of devices, analyzing the physical properties of materials, allow you to accurately determine the amount of vapors in the air.

Hair device consists of synthetic hair, defatted hair, base with scale, arrow and pulley. With an increase or decrease in vapors, the tension force of the hair changes, the pulley turns, changing the position of the arrow on the scale with values.

Such a meter operates in the range from 30 to 80%. Now it is practically not used, since there are other models that have a wider range of work.

IN film moisture meter an organic film attached to the pulley acts as a sensing element. When the humidity indicator changes, the film tension increases or decreases, which leads to the movement of the pulley, which changes the angle of inclination of the arrow.

The pointer moves along an arc-shaped dial, showing the percentage of humidity in the room.

Both mechanisms operate according to the laws of mechanics, so they can accurately measure moisture in rooms where the temperature is low, up to 0 ° C.

Weighing and condensation meters

Through weight hygrometer you can determine the absolute humidity. Such a device is used for laboratory experiments, so it is not suitable for indoor use at home.

Condensation meter summarizes the most accurate data. The design of such a device consists of a flat surface on which moisture settles, a thermometer that determines the moment of condensation formation and a beam of light that captures the appearance of the first condensate. The working range of the meter is from 0 to 100%.

These mechanisms generate results with high accuracy, which is necessary for research, but not as home air humidity meters.

Mechanical and electrical appliances

Mechanical or a ceramic moisture meter works by means of the electrical resistance of the mass. Since the composition of the ceramic mass contains silicon and kaolin with metal particles, the resulting mixture changes resistance after a change in air humidity.

We bring to the norm

To ensure a comfortable stay, it is necessary to regulate the relative humidity of the air. This requires:

Ventilate the premises regularly, at least twice a day. It is best to do this after waking up and before bed. In winter, it is better to carry out short ventilation times with a wide open window to prevent cooling of the walls and floor. In summer, when the amount of moisture outside is not enough, you can not open the windows wide for a long time.
Increase the number of indoor plants. Moistening occurs due to the evaporation of moisture from the soil surface. Shriveled, drooping, dried leaves will indicate a lack of moisture in the air.
Set up an aquarium. Evaporation of water from its surface greatly humidifies the air. This is noticeable even without measurements. If you do not want to engage in aquaristics, you can place containers with water in the apartment. Not so aesthetically pleasing, but very practical.
Carry out wet cleaning regularly. The absence of dust will allow more moisture to be suspended.
Purchase a special humidifier. This is especially true if there are infants and young children.
Spray water with a spray bottle for watering plants or ironing clothes.

AQUARIUM AND AIR HUMIDITY

It doesn't matter whether you choose one method or you will use a set of activities. The main thing is that the temperature and humidity indicators are within normal limits.

We need the right moisture, moisture is very important to us. Such a main conclusion can be made by reading the article. Maintain the air humidity in the apartment within normal limits, take care of your own health.

What to look for when buying?

Indoor models of devices for measuring the amount of moisture in the air include mechanical and electronic hygrometers. They have a compact design, are safe for others and give minimal error in calculations. To support the design idea, modern devices have a laconic design.

Criterion # 1 - how it works

Mechanical hygrometers and digital hygrometers have a number of advantages that can influence instrument selection.

The advantages of mechanical models of moisture meters include:

the operation of the device does not depend on external power sources;
they are easy to use, since minimal additional adjustment of the required operating parameters is required;
the cost of a mechanical hygrometer is somewhat lower than an electronic one.

Digital models are made as foldable, portable gadgets.

In addition, the advantages of electronic models include:

high speed of issuing the result;
less error of indications, in comparison with a mechanical device;
the output data is subject to further processing due to the presence of built-in internal memory.

Some electronic moisture meters combine several devices at once: a hygrometer, clock, calendar, thermometer, barometer, dew point meter. Therefore, if the device performs several climatic functions, it is fixed weather station.

For the comfort of the child and parents, the hygrometer can be built into the baby monitor. Such a device has great functionality and a warning system.

The latest models are equipped with a Wi-Fi module to display information about the weather in the region by receiving data via the Internet.

Modern models of hygrometers are designed for a certain specificity of work, therefore, in order to accurately measure the humidity in a room, apartment or other premises, it is necessary to understand how the device will be used. Then the purchased moisture meter will fully meet the necessary requirements.

Criterion # 2 - Humidity Range

The optimum air humidity is determined by the purpose of the premises. In the bedrooms, living room, the normal values of the moisture meter are from 20 to 80%. Near the balcony, in the lobby, attic and in the kitchen from 10 to 90%. We recommend reading more about the humidity standards in the apartment in this material.

In wet rooms, the operating range can be up to 100%. The wider the range of values captured by the device, the higher the price for it. Therefore, when choosing a gadget for bedrooms, halls and attic spaces, you can opt for devices with a small range of values.

For some moisture meters, the maximum heating threshold is important. So, a device for a bath or sauna should include values up to 120 ° C in the operating temperature range. Therefore, in rooms where temperature and humidity can reach rather high values, special devices should be purchased for measuring vapors in the air.

Criterion # 3 - Measurement Accuracy

For the equipment of special storage facilities, devices with the smallest indication error are required.

So, in a home winery, the humidity of the circulated air should be kept at the level of 65-75%, and the water vapor content in the library should not be lower than 50 and above 60%.

Therefore, to measure moisture in the air in such rooms, a psychrometer or a high-precision electronic hygrometer should be used, which measures the amount of water vapor by changing the electrical conductivity of the air.

If the humidity level does not meet the standards, but you need a device to increase it - a humidifier.

findings

Awareness of the state of humidity in the air allows you to avoid many unpleasant and even dangerous consequences for health. This is what devices such as hygrometers are for. The range of such devices is very diverse, which will allow the buyer to choose a hygrometer that will meet all the requirements.

When choosing a hygrometer from various existing models, you should pay attention to the accuracy of the air humidity indicators provided by the device. Not every buyer needs ultra-accurate hygrometer readings, content with relative ones.

Also, when choosing a hygrometer, you should very carefully check all its technical characteristics. A spontaneously chosen hygrometer may not perform all the declared functions, which will affect both the nerves and the mood. Wasted money will certainly not add to your joy. In order to avoid such troubles, it is imperative to take a receipt upon purchase. It should always be possible to return a defective product back to the store.