What a hygrometer consists of: diagram and device

Any construction project’s strength and longevity depend on an understanding of the moisture content of the concrete. In order to measure these levels accurately, a hygrometer is a commonly used tool. This tool aids in determining the concrete’s humidity content, which may have an impact on the material’s overall performance and curing time.

Despite its apparent complexity, a hygrometer is actually composed of a number of simple parts. The device’s main components are a sensor that measures moisture content and a display that shows the results. When combined, these components offer insightful information that can direct building choices.

A hygrometer’s main components, including the digital or analog display, the moisture sensor, and occasionally a concrete-inserting probe, are usually depicted in the diagram. This arrangement makes it possible to take exact measurements, which helps prevent problems that could arise from too much moisture, like the concrete weakening or cracking.

Gaining an understanding of the parts and operation of a hygrometer will help you use it more efficiently. This information is a useful addition to any builder’s toolkit since it is crucial for preserving the durability and quality of concrete structures.

Part	Description
Sensing Element	Measures the humidity level in the air
Display	Shows the humidity reading, can be digital or analog
Power Source	Provides energy to the device, usually batteries
Housing	Protects the internal components and holds the device together
Calibration Controls	Allows for adjustment to ensure accurate readings
Mounting Options	Ways to position or hang the hygrometer, like hooks or stands

A hygrometer is a vital instrument for determining the relative humidity in a variety of settings, including home basements and construction sites. Usually, this gadget has a sensor to find moisture in the air and a display to show the relative humidity. In this post, we’ll dissect a hygrometer’s parts, offer a clear diagram for comprehension, and discuss the practical operation of the instrument. This guide will assist you in comprehending the inner workings of this vital instrument, regardless of whether you’re a professional in the field or a curious do-it-yourself enthusiast.

How a humidity measuring device works?

Regardless of the level of measurement accuracy and design, all hygrometers—whether sold commercially or provided to specialized laboratories—comprising the following primary and secondary functional components:

• The body, or tripod, which is equipped with a stand for installation on the table, as well as a frame for attaching the main parts of the equipment.
• Sensors that are designed to respond to air humidity and transmit a mechanical or electrical signal to the actuator. A nylon thread, a thin polymer membrane, a mirror plate for collecting condensate, or a pair of thermometers – wet and dry – can act as sensors.
• An actuator with an arrow, a spring mechanism, or an electronic unit that is driven by a pulse transmitted from the sensor.
• An information scale or LCD display that displays the device"s readings – an arrow or an electronic program code.
• A counterweight for the arrow – in mechanical hygrometers, which allows the part to return to its original position when resetting the settings.
• For electronic moisture meters – a control panel that allows you to set the current settings and calibrate the device.

The hygrometer is typically sold assembled and packaged by the manufacturer. If the user needs to put this device together, there is a diagram with detailed instructions and an illustrated description that comes with it.

Structural elements, sensors for different types

Since the first mechanical hygrometers were introduced many years ago, hundreds of models from numerous manufacturers are currently available on the market. Every hygrometer modification has a unique internal structure.

The features, components, designs, diagrams, sensors, actuators, and other structural or functional components of every type of hygrometer that is available for purchase or use in testing facilities are described in detail below.

Hair

One of the most basic types of mechanical hygrometers is found in hair, which has the following structure:

• The tripod of the device design is a vertically elongated rectangular frame made of steel or high-strength plastic
• A stand with rubberized feet made of the same material as the tripod.
• Fasteners at the top and bottom of the tripod with threaded tightening elements for attaching a nylon cord.
• A nylon cord or hair that is stretched between two clamps and connected to the spring mechanism of the actuator. The hair in this device acts as a sensor.
• The actuator in the form of a spring mechanism that is activated when the hair is pulled or loosened, depending on the change in relative humidity.
• An arrow attached to the spring mechanism and deflected when it is triggered.
• An arc-shaped graduated scale on which marks are applied indicating the percentage of water vapor in the air. When the arrow is deflected, its sharp edge points precisely to the current state of the measured gaseous substance.

It should be noted that, if the equipment is operated under typical circumstances, the hair for devices in this category is a consumable component that needs to be replaced every six to twelve months owing to physical wear.

Film

The following design features set film hygrometers apart from hair hygrometers, despite their operational principles being very similar:

• The frame and stand for this device are made in the same shape as for hair hygrometers.
• In the lower half of the frame, near one of its vertical supports, there is a ring retainer consisting of two rings of different diameters and a tightening screw with a lock nut.
• The polymer membrane is stretched over the small ring so that its edges protrude beyond the locking element along the entire perimeter.
• After stretching the film, the entire structure is covered with a ring of a larger diameter and tightened with a screw, after which it is attached to the hygrometer stand.
• A washer is installed in the center of the polymer membrane, to which a thread is attached, connecting it to the spring actuator. The ring with the polymer membrane, in this case, acts as a sensor.
• A vertical steel arrow is fixed to the actuator on a hinged support.
• A scale is mounted in the upper part of the device, the shape, size and number of divisions of which are identical to a hair hygrometer.
• The finished structure is installed on the floor or on a table using rubberized inserts, and, in some cases,. the upper part of the frame crossbar has lugs for fixing to the wall.

Both the nylon hair and the film membrane are susceptible to physical wear. Consequently, it is imperative to promptly restock on multiple films in order to rule out hygrometer malfunctions and inaccurate readings.

Weighing

Compared to the other two types of metrological equipment, weighing hygrometers are more intricate pieces of machinery. The following primary and secondary components are included in the design of such devices:

• A weighing hygrometer is also called absolute, due to its design and increased accuracy.
• The sensors are 2 to 4 steel or glass tubes with a diameter of 15 to 25 mm, U-shaped and connected to each other by flexible hoses.
• Inside the tubes there is a hygroscopic substance that effectively absorbs water vapor from the surrounding air.
• At the base of the outer tube there is a manual or electromechanical pump through which air is pumped. It is for this volume of air that the relative humidity must be determined.
• The system of tubes is connected to an actuator on which several arrows with dials with different designations are arranged to indicate the measurement results.
• To block the air mass of the substance being tested, manual valves are located at the ends of each of the tubes.
• The readings of the arrows allow you to determine the volume of air, the mass of the entire system before pumping it with humidified gas from the atmosphere and after its injection, when the hygroscopic substance draws water molecules from it.
• Based on the results of simple measurements, the absolute humidity of the air is first found, and, taking into account its volume, the relative parameter of the water vapor content is calculated in percent.

Despite the global use of digital metrology equipment, weighing devices are still frequently utilized in testing laboratories due to their high degree of accuracy.

Ceramic

Ceramic hygrometers are high-end, luxury items in the expensive range. They have the following design components, which measure air humidity:

• The body of the device combines sensors and an actuator, as well as indicators. It is made in the form of a flat cylindrical dial with an arrow behind the glass.
• A graduated scale is located at the back of the arrow, on which there are marks indicating air humidity from 0% to 100%.
• As the arrow rotates, its pointed end stops opposite one of the readings on the scale, which means the amount of water vapor in the measured air.
• Inside the hygrometer there is a mass of ceramic crystals, which are poured between plates of conductive steel. These elements act as sensors.
• Ceramic crystals are dielectrics, and steel plates are conductors, as is the water contained in the air.
• As air passes through the porous backfill, the electrolyte in the form of water interacts with the metal, after which electrical impulses set in motion a circular spring with an actuator.
• As the spring is compressed or weakened, the arrow on the front side of the metrology equipment begins to deflect and show the exact content of relative humidity in the air.

Because this high-precision equipment frequently fails as a result of impact loads and other impulse mechanical effects, it is advised that you use extreme caution when using it.

Electrolytic

Since water molecules are a liquid and an electrolyte, electrolytic devices work by measuring the electrical permeability of air, which rises when the air becomes saturated with them.

This apparatus is composed of the following components:

• The body of the device is a glass or steel hollow tube with an internal diameter of up to 40 mm.
• A non-combustible fibrous insulating material – mineral or basalt wool – is glued along the inner perimeter of the hygrometer tube, which eliminates the penetration of sound vibrations into the control chamber.
• The coating of the insulators is covered with a liquid composition that conducts electricity, most often, a compound of chlorine with lithium.
• After applying the electrolyte, the tube is treated from the inside with polymer binders to improve the adhesion of the elements.
• A conventional alcohol or mercury thermometer is installed at the exit of the tube to measure the air temperature.
• When the humidity in the air changes, or the temperature rises, the electrolyte begins to increase, and the size. In this device, the liquid electrolytic compound is a sensor.
• As the volume increases, the electrolyte acts on the piston base, pushing it along the rod, which in turn is connected to the actuator of the hygrometer – a spring.
• An arrow is attached to the spring, which is located inside a circular dial with a scale of relative air humidity.
• When you press the spring, it is compressed, the arrow rotates and is fixed at a certain division of the dial.
• Modern electrolytic hygrometers can be equipped not only with an arrow, but also with an electronic dial with an LCD display.

Since the electric discharge of these devices can pass through nearly dry gaseous substances and produce accurate readings on the electrolytic hygrometer’s indicator, they are unique in that they can measure a wide range of airborne water molecule concentrations.

Condensation

Because condensation metrology equipment can function in a wide temperature range, it is common to use it both indoors and outdoors to measure air humidity. The following functional and design elements make up these devices:

• Condensation hygrometers are used today mainly in laboratories, since, despite the increased accuracy of readings, they are too large and involve wet processes.
• Inside the steel cylindrical box there is a set of plates with silvering to achieve a mirror shine. These mirror plates are the sensors of the condensation hygrometer.
• From the end side, a cylinder with a diameter of up to 100 – 150 mm is connected to a ring on which a circular dial and an arrow with a spring actuator are located.
• A nipple made of a steel tube is welded to one of the faces of the cylinder, on which a polymer hose with a bulb is fixed.
• As atmospheric air is pumped into the body of the cylinder using a bulb, moisture from it is deposited on the surface of the mirror in the form of droplets of water or ice crystals, depending on the temperature of the air environment.
• The volume inside the cylinder is known in advance, and, depending on the mass and accumulated condensate from the air, the relative humidity of the air is calculated.
• The actuator reacts to the increase in pressure inside the cylinder, when the condensate begins to displace the air, which sets the arrow in motion.

The air quality is one of the primary challenges in the operation of such hygrometers. Therefore, the sensors rapidly become confused if contaminated moisture droplets land on the mirror, resulting in inaccurate readings. Periodic cleaning and maintenance of the condensation device is necessary to remove these issues.

Psychrometric

Psychrometric hygrometers are among the earliest instruments used to gauge air moisture content. The structure and principle of operation of these mechanisms are extremely simple:

• On a flat, usually plastic, rectangular stand up to 300 – 400 mm high and up to 100 mm wide, a psychrometric table is marked. This information scale is the dependence of relative humidity on the difference in readings of two tremors – dry and wet.
• Two thermometers with alcohol or mercury content act as sensors, which are placed along the vertical plane of the tripod.
• One of the thermometers is immersed in a flask with water or a damp sponge, which is why it is called wet.
• The tripod is fixed on a stand with legs for convenient placement on a horizontal plane.
• As the air temperature in the room is measured, the dry thermometer always shows a higher value than the wet one.
• When the user needs to determine the relative humidity of the air, he just needs to take readings sequentially from the dry and wet thermometers, calculate the difference between these results, and then substitute the values ​​​​in the psychronometric table.
• By resorting to the method of interpolation between 2 or 4 adjacent values, it is easy to calculate the correct indicator of the percentage of water vapor in the air with a minimum error.
• Some psychrometric hygrometers are also equipped with a wet-bulb humidity level indicator, which allows you to add water to the flask or sponge in time to make the readings more accurate.

It is advised to replace the sponge or water bath on the wet-bulb thermometer periodically in order to maintain constant moisture levels for accurate readings. When drying, the user compares the wet-bulb readings with the dry one, making it impossible for them to discern the difference. As a result, they must use the psychrometric table to calculate the relative humidity of the air.

Capacitive

Among the earliest and most useful kinds of devices are capacitive hygrometers, which are made up of the following components:

• A thin polymer membrane, characterized by hygroscopic properties, acts as a sensor for determining the level of humidity in the atmosphere.
• Metal electrodes are fixed on both sides of the flat membrane, which consist of fibers tightly woven together, ensuring the porosity of the conductive elements.
• The entire structure of the film and conductive contacts in the form of a sandwich is installed inside a plastic case on a stand.
• As water is absorbed from the air, the polymer membrane increases in volume, which causes a change in the dimensions of the pores between the electrodes.
• As the dielectric medium is saturated with water molecules, the tensors of the actuator change in volume, which sets the spring of the pointer indicator in motion.
• On the back of the hygrometer arrow is a scale with readings of the relative humidity of the air, which accurately allows you to determine the current content of water vapor.
• If the relative humidity of the air drops, the polymer sensor decreases in volume, and the actuator sets the arrow in motion in the opposite direction.

If you have the right tool, basic steel and plastic parts, and instructions on how to put each component together and process it, you can assemble capacitor devices by hand.

Resistive

The following design components are included in resistive hygrometers, which are distinguished by their high accuracy and increased assembly complexity:

• Sensors in such a metrological device are 2 opposite-pole electrodes, which are placed on a dielectric flat substrate.
• A hygroscopic membrane with increased electrical conductivity is fixed above the substrate.
• As the hygroscopic layer is saturated with moisture, the material changes in volume.
• Hygrometer sensors have very low resistance since they consist of aluminum components.
• The resistance of the electrodes changes as the hygroscopic material is saturated with moisture, which allows you to obtain information about its amount in the air. The operating principle of such hygrometers is based on the analysis of the resistance of the conductive medium when an electric charge passes through water molecules. The higher the resistance, the lower the relative humidity of the air, and vice versa.
• Electrodes with a substrate are placed in a plastic or metal housing, on both sides of which there are contact terminals for connecting the sensors with the device and the electronic module.
• The contacts are connected to indicators, which are a dial with an arrow or a liquid crystal display.
• Such hygrometers, as a rule, operate on batteries or rechargeable batteries located in a special compartment on the back. The simple design makes them available for household use.
• Some resistive hygrometers are equipped with a control panel with the ability to record readings.

It is advised that you become familiar with the operating manual of resistive hygrometers beforehand or view a number of online video tutorials and master classes taught by professionals who frequently make their videos available to the public.

Optical

High-quality lenses set apart optical metrology instruments for measuring the amount of water vapor in the air. These instruments include the following functional and design elements:

• The hygrometer sensor, which identifies the amount of moisture, is a thin rectangular mirror plate with silvering, on which condensation from the air accumulates if the surface temperature is equivalent to the dew point.
• Above the mirror is a light-emitting diode, generating a light beam at an angle of 30 – 45 degrees relative to the plane of reflection.
• The beam directed from the light-emitting diode is reflected from the flat surface of the mirror and is captured by a photocell located strictly along the trajectory of the angle of reflection, according to the laws of optics.
• When a beam of light falls on the mirror plane, the temperature of the material increases slightly.
• On the back of the mirror there is a temperature control module that determines the dew point, which causes condensation.
• The mirror also has a temperature sensor that responds to the slightest fluctuations in the temperature and humidity parameters of the environment.
• After condensation, the actuator reads the temperature and absolute humidity values, transmits this information to the electronic unit.
• In the electronic module, information is processed in accordance with a programmed algorithm, formulas of elementary physics, and the final data is received in the form of a digital code on the screen of the genimeter in the form of a percentage of humidity per unit volume of ambient air.

Since optical instruments can measure water vapor in the air to tenths or even hundredths of a percent accuracy, they are frequently installed in warehouses with higher requirements for temperature-humidity and climate.

Thermistor

The following components are included in the design of thermostat hygrometers, which are sophisticated mechanical or electrical metrology instruments with an accuracy of up to 0.01%:

• A thermistor is a semiconductor element whose electrical resistance constantly changes in direct proportion to the change in its temperature.
• Thermistor-type hygrometers are equipped with a pair of identical thermistors covered with polymer dielectric insulation.
• The first thermistor is sealed in a completely sealed chamber, into which water molecules do not have access.
• The second thermistor is placed in the same chamber, but with perforated walls.
• Both thermistors act as sensitive sensors in this hygrometer.
• A compact device in a plastic case on a stand, inside which there are two different chambers with thermistors, is installed on a table.
• Both thermistors respond to changes in ambient temperature, but show different values.
• A dry thermistor has an electrical resistance that differs from a similar reading for a wet thermistor by a certain value.
• Information about the resistance of each thermistor is sent to the electronic units of the hygrometer actuator.
• When analyzing the difference between the resistance values, in accordance with the algorithm of the linear relationship between electrical conductivity and the amount of humidity embedded in the electronic unit.
• The received information is processed automatically and transmitted to the device screen.
• Thus, the higher the difference between the resistances of the thermistors, the greater the relative humidity, and the user reads this information from the hygrometer screen.

These days, thermometer hygrometers are rare to find on the market since electronic and digital devices have long since supplanted them. Simultaneously, in certain testing or educational facilities, this kind of equipment is included in the balance sheet and serves its purpose effectively.

Why is it important to know the device?

For the following reasons, every hygrometer user and purchaser needs to be familiar with its design, schematic, and working principle:

• Possibility of trouble-free operation of the hygrometer without turning to professionals.
• Possibility of self-adjustment of verification and calibration of the hygrometer.
• In case of failure of the metrological equipment, the user will be able to independently carry out minor repairs or replace the consumable element.
• Use of the full functionality of each device to measure the amount of moisture in the air.
• Assessment of the degree of safety, precise knowledge of climatic and temperature-humidity restrictions, making a decision on the final choice and purchase of the device after determining the feasibility of purchasing the modification in question.
• The ability to independently compare indicators with subsequent assessment of errors when using various metrological equipment in laboratory conditions.
• The opportunity to transfer your experience, train users, acquire new skills in life.
• The ability to independently develop working drawings with subsequent assembly of a simple mechanical hygrometer with your own hands, which can significantly reduce the cost of purchasing devices of this category with their subsequent maintenance.

If the hygrometer’s design is not understood, the user runs the risk of paying a large amount of money for both repairs and maintenance, which are typically doable without the need for costly service center specialists. These tasks include checking or calibrating the device.

It is essential to comprehend the parts and operation of a hygrometer in order to measure humidity levels precisely. This gadget, which usually consists of a sensor, display, and power supply, is essential for a number of uses, including environmental monitoring and construction.

The sensor, which measures the amount of moisture in the air, is the hygrometer’s brains. Depending on the kind, it may employ materials that respond to variations in humidity, such as polymers or salt solutions. The hygrometer can then interpret the electrical signal that is produced by this reaction.

The humidity reading is presented on the display in an understandable format, frequently expressed as a percentage. While older models of hygrometers might have analog dials, more recent models may have digital displays for improved readability and accuracy.

Hygrometer power sources are not all the same. Plug-in models are best suited for stationary applications where continuous monitoring is required, while battery-operated models offer portability—a feature that is particularly helpful in fieldwork.

Understanding the components and operation of a hygrometer will help you manage humidity in your projects appropriately. Having accurate measurements of humidity is crucial for getting the best results, whether you’re working on the curing of concrete or maintaining indoor air quality.

Video on the topic

Design and principle of operation of the VIT 1 psychrometer

Operating principle of hygrometer and psychrometer

Humidity sensor "HYGROMETER" how to make an automatic drying SCHEME /Dmitry Kompanets/

Experiments in physics. Design and principle of operation of a psychrometer

Setting the humidity readings in the DC-803 hygrometer

How a hair hygrometer works