In this work, I present three types of humidity sensors and their scope of application. The most commonly used humidity sensors are based on capacitive or resistive measurements. All of these types of humidity sensors have a comparable design, which uses an insulated substrate, electrode structures, and sensing material. The choice of a suitable sensor manufacture (in case of technical specifications) depends on the operating conditions. The impact of humidity plays an important role in all areas of human life such as biology or automated industrial processes because water vapor is a natural component of air. Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”?Get the original essayMoisture sensors are used in intelligent systems to monitor soil moisture in agriculture or for monitor corrosion and erosion in infrastructure. Additionally, humidity sensors are used to address human comfort issues in home applications. Due to the different application areas of humidity sensors and the different associated requirements, there are different sensor principles. Based on the units of measurement, these sensors are divided into two main groups: relative humidity sensors (abbreviated RH) and absolute humidity sensors (abbreviated AH). ) sensors. These types of sensors are called hygrometric sensors. However, in many humidity measurement applications, relative humidity measurement is preferred because relative humidity measurement is simpler and therefore less expensive and is widely used in air quality fields. indoor air and comfort problems. To make humidity sensors flexible for a wide application range, the following requirements, such as short response time, low hysteresis and good sensitivity over a wide humidity and temperature range, are imposed on these sensors. As the most commonly used method is measuring relative humidity, relative humidity is explained below. In general, humidity is defined as the amount of water vapor present in an air atmosphere. Relative humidity being a variable dependent on temperature, it is customary in hygrometry to measure humidity at the same time as temperature. Relative humidity is given as a percentage and determined as follows: where: pw: water vapor pressure, ps: saturation pressure at the same temperature given in Bar. Humidity sensors based on the change in their electrical properties are divided into two groups: resistive- type and capacitive type. The construction of capacitive sensors and resistive sensors is comparable, but the measuring principle is different. Capacitive type sensors are based on changing their dielectric properties, while resistive type sensors are based on changing their conductivity. Both types of sensors feature a pair of electrodes on a substrate covered with a moisture-sensitive layer. The adsorption of water vapor causes a change in the dielectric constant of the material (capacitive type), which leads to a change in the capacitance between the electrodes, or a change in the conductivity of the material (resistive type), which makes as the resistance changes. As a substrate, an alumina substrate was selected. On this substrate are the electrodes, for this an interdigital structure (or comb structure) with intervals of 0.15 mm was chosen. The moisture-sensitive layer consists of a mixed aqueous solution of styrene-sulfonate monomers,crosslinking and vinyl polymers which are spin-cast onto the substrate. Since the styrene sulfonate is polymerized and cross-linked by ultraviolet irradiation, the coated film is irradiated by ultraviolet light in a nitrogen atmosphere. For protection, the moisture-sensitive layer is covered with a moisture-permeable film. This protective film serves to remove influences such as cigarette smoke, oil and other impurities, and to protect the moisture-sensitive film from them. The sensor size is 5 mm x 7 mm. Using a thermostatic humidity generator, the resistance was measured at different relative humidities. For the measurement, the sensor was connected to a load resistor and an alternating voltage of less than 3 V was applied. The accuracy of humidity generated in the thermostatic test chamber is better than 2% RH. The sensor exhibits high sensitivity on relative humidity and, as expected, logarithmic behavior and has the advantage of being linear in the range 30% to 100%. Since many sensors were produced on the same substrate, the response characteristics are comparable and show the same behavior. The curve with the solid line shows the response of the sensor with a protective layer and the curve with the dotted line shows the response of the sensor with a protective layer. sensor without protective layer. Response time is measured for a rapid change in relative humidity from 30% to 90% and vice versa. For the sensor with a protective layer, the response time for adsorption and desorption is a few seconds. For the sensor without protective layer, the response time is 100 seconds for adsorption and 150 seconds for desorption. This sensor is called "Humicape" and was developed by Vaisala in Finland and is used in many humidity measuring instruments, such as radio waves. probes. As a substrate, a glass substrate was chosen. On this substrate, the lower twin electrodes are fixed by evaporation of indium. The thin-film moisture-sensitive material used is cellulose acetate with a thickness of approximately 1 µm. Above is the upper electrode which is made by evaporation of gold. This top electrode is approximately 10 nm to 20 nm thick and is porous enough for water vapor transport. The upper electrode, which acts as a counter electrode to the lower twin electrodes, results in a series connection of two capacitors. This construction has the advantage of eliminating contact difficulties with the thin upper electrode. Capacity is approximately proportional to ambient humidity in the range 0% to 100%. The sensor has good accuracy and a response time of about 1 s to reach 90% of the steady-state value. As substrate, an alumina substrate was selected. On this substrate are the electrodes, for this an interdigital gold structure (or comb structure) with a thickness of 8 µm to 10 µm was chosen. The humidity-sensitive layer was prepared with different mixing ratios of GTMAC (glycidyl trimethylammonium chloride), PPGDE (polypropylene glycol diglycidyl), and MTHPA (methyl tetrahydrophthalic anhydride). Figure 7 shows the sensor response characteristics at 25°C and 1 kHz for a mixed ratio GTMAC/PPGDE/MTHPA = 100/0/70. For the measurements, an alternating voltage of 1 V was applied between the electrodes. The sensor impedance was measured in the range of 30% to 100%. The absorption and desorption curve shows a proportional behavior. For the determination of the hysteresis, two dotted lines in the range of +- 2% RH are shown in Figure 2. For the sensor hysteresis, this gives a value.