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The humidity sensors are found in various materials, measuring humidity between 30-90% and mostly room temperature. And the main types of analog humidity sensor include:
Capacitive Humidity Sensors
A capacitive humidity sensor detects humidity by measuring relative capacitance between two conductive plates separated by a dielectric (insulating) substrate). As the humidity level increases, water vapor molecules penetrate the dielectric material, causing the dielectric constant to increase and the capacitance between the plates to change.
Resistive Humidity Sensors
The resistive humidity sensor works by measuring electrical resistance between two electrodes. The sensor uses a hygroscopic (moisture-absorbing) material. When moisture is absorbed by the material, it creates a conductive solution between the two electrodes through the creation of electrolytic solution.
Thermal Conductivity Humidity Sensors
A thermal conductivity sensor uses the principle of difference in thermal conductivity between dry and moist gases. The sensor contains two thermistors (temperature-sensitive resistors) or temperature sensors in two different chambers. One chamber measures dry air and the other moisture.
Resonant Cavity Sensors
These sensors function by measuring changes in resonance frequency of an acoustic (sound) or electromagnetic cavity with the humidity level. Common resonant elements include surface acoustic waves (SAW) or other resonators like quartz.
Inductive Humidity Sensors
Inductive humidity sensors function by measuring inductance changes between two coils as the moisture level changes. With increasing humidity, the moisture level alters the dielectric constant of the air between the coils, resulting in capacitance variation that is directly proportional to the humidity.
All these sensors are made from different materials to ensure good performance in terms of durability.
Capacitive Sensors
The element is usually made from ceramic, polymer, or metal oxide. The dielectric (insulating) material between the plates is often a polymer that absorbs moisture. Ceramic and polymer are solid materials with high durability and therefore can be used in harsh environments. They will also bear extreme humidity. Capacitive sensors are usually sealed with epoxy or silicone to protect them from the environment and moisture and to make the sensor durable.
Resistive Sensors
The measurement electrodes are typically made from materials like silver, carbon, or other conductive metals. The sensing element is usually a polymer or salt that absorbs moisture. Salts or polymers are delicate materials and will wear out with time, especially when exposed to moisture. Resistive sensors are sealed in protective housings made from metals, plastics, or ceramics, which protect them from damage.
Thermal Conductivity Sensors
Thermistor or temperature sensors are often made of materials like nickel, platinum, or silicon, which are very durable and can withstand harsh conditions. The chamber can be made of metals or other durable materials which can withstand high temperature or pressure. The use of solid materials, like metals, makes the chamber very durable.
Resonant Cavity Sensors
These elements can be made of materials like quartz, ceramics, or metals. An example of a resonator is surface acoustic waves (SAW), which uses piezoelectric materials like quartz or ceramics. These materials are very durable and can respond to humidity changes for many years. Cavity sensors are placed in protective housings of metals or plastics to prevent them from breaking.
Inductive Sensors
The coils are typically made of durable metals like copper or aluminum. The dielectric between the coils can be air, a solid, or liquid, depending on the design. Coils are made from strong metals, making them durable and practical for measuring humidity. The housings, in which coils are enclosed, are made from other durable materials to protect them and the dielectric.
HVAC Systems
Analog humidity sensors are mostly used in HVAC systems to control humidity levels in residential and commercial buildings. By providing accurate readings, the sensors help maintain a comfortable indoor environment, reduce energy consumption, and prevent issues like mold growth and structural damage.
Greenhouses and Agriculture
In agriculture, humidity sensors help monitor and control humidity levels in greenhouses. They help optimize plant growth, prevent diseases, and increase crop yields. They are used in smart irrigation systems to achieve better resource efficiency and lower costs.
Food Processing and Storage
The food industry uses humidity sensors to control and monitor humidity levels in processes and storage conditions. This prevents spoilage, extends shelf life, and maintains the quality of food products. In warehouses, sensors help control humidity to ensure the quality of perishable goods.
Pharmaceutical Industry
Humidity control is important during the manufacturing and storage processes of drugs in the pharmaceutical industry. Exposure to high humidity can degrade drug products and affect their quality and efficacy. Humidity sensor in vitro helps ensure compliance with regulations and prevent product loss.
Textile and Paper Industry
Textiles and papers expand and contract due to humidity changes, affecting storage, production, and quality. Humidity sensors help control and monitor levels in these industries to help maintain product quality, prevent damage, and ensure optimal production conditions.
Smart Home Devices
The sensors are integrated into smart home systems to provide users with real-time humidity data and automatic control of dehumidifiers, humidifiers, and ventilation systems. This contributes to improved indoor air quality, comfort, and energy efficiency.
Measurement Range
This factor means what range of humidity levels is the intended application? Will it require from low to high humidity levels? Pick a sensor that has the appropriate measurement range for the application. Using a sensor outside its range can lead to inaccurate readings.
Sensitivity and Accuracy
Select a sensor with a proper degree of accuracy and sensitivity for its application. High-sensitivity sensors are used in processes that require precise humidity control, such as pharmaceuticals and electronics. Less sensitive ones are used in applications like weather monitoring.
Response Time
Analog humidity sensors should respond quickly to level changes, especially in applications like HVAC and greenhouses, where timely adjustments are crucial to obey comfort and maintain optimal conditions. Slower response time can be acceptable in applications that don’t need real-time data, like storage monitoring.
Environmental Conditions
Humidity sensors are designed to operate in specific environments. Consider factors like temperature, pressure, and exposure to moisture, chemicals, or dust when choosing a sensor. Ensure the sensor materials and housing are durable enough to withstand harsh environmental conditions.
Compatibility
Ensure the sensor outputs are compatible with existing systems and equipment. Check the compatibility with data loggers, controllers, or other monitoring devices used in the system. This will ensure that the sensor integrates easily without requiring significant modifications.
Maintenance and Calibration
Consider the maintenance requirements and the periodic system calibration of the sensor. Some sensors need frequent recalibration or maintenance, whereas others will need little care. Choose the one that will fit in with the resources and time needed for the maintenance of the system.
A1: Some humidity sensors can work in that kind of environment. Yet, the capacitive and resistive sensors might not work because of the deposition of corrosive material on the surface. Thermistor sensors might work in high humidity, and resonant humidity sensors may work in high-heat environments.
A2: The performance of resistive humidity sensors will be affected by temperature and contamination. Other factors include chemical exposure and mechanical damage to the hygroscopic material. These factors will change the electrical resistance between the electrodes, thus affecting the sensor performance.
A3: The maintenance the sensors require is periodic cleaning, calibration, and sometimes replacing the hygroscopic materials in them. Environmental factors like dust, condensation, or chemical vapors might contaminate the sensor, resulting in inaccurate readings. Regularly cleaning the sensor and recalibrating it helps ensure accurate performance.
A4: Using protective enclosures, filtering the air to reduce particulate matter, and using less sensitive sensors in harsh environments will help increase the sensor life. Regular maintenance and choosing a sensor compatible with the application’s requirements also contribute to longer sensor life.
A5: The sensors help control moisture in the soil, and with that, it gets to optimize irrigation and crop growth. They help maximize resource usage to improve crop yield. Additionally, they monitor the condition of stored grains to protect them from spoilage.
