Did you know that an HVAC in a critical pharmaceutical environment can have as many as 200-1000 humidity and temperature sensors? The use of temperature and humidity sensors goes beyond HVAC applications. They are vital to food and beverage processing, power plant processes, data centers, server rooms, weather stations, health care centers, IoT devices, and more. However, their shape, types, and sensing capabilities can vary.
Humidity and temperature sensors may look like simple instruments but vary by application. Considering the technical aspects, finding your system's ideal temperature and humidity sensor can help save money and time. This ultimate guide will provide one-stop, in-depth information on temperature and humidity sensors. Let's get into it!
Overview and Working Principles of Temperature and Humidity Sensors
Sensing the temperature and humidity of air or fluid passing through a pipe or duct is vital to adjusting heating and cooling requirements. It provides valuable insights into the process that leads to higher-quality output. Learning how temperature and humidity sensors work and their purpose can help us find the right one for our application.
What are Temperature and Humidity Sensors?
Temperature and humidity sensors can detect environmental changes around their sensing parts to provide feedback to the controller for adjustment. These sensors can only be inside a motor, pipeline, or room atmosphere to monitor and give the user information. Their latest integration with smart home technology has further increased their significance.
Modern homes have smartphone applications coupled with a smart home thermostat. Its purpose is to control all their home heating and cooling devices. Your home could have a floor, pool water, domestic water, indoor air, and many other temperature control devices, such as heat pumps and air conditioners. All of them will have temperature sensors that report the temperature conditions to the thermostat and adjust the control device's output to provide a comfortable water, floor, and air atmosphere.
In industrial applications, these temperature and humidity sensors detect the air or process conditions and convert them into electrical signals. Controllers detect these electrical signals, convert them into valuable data, and control the process to enhance productivity. Even the device you use to read the article has temperature sensors for overheating protection.
Working Principle of Temperature Sensors
The technology to sense temperature has changed since 1592. Detecting contraction in a fixed air mass when moving from a hot to a cool environment represented the temperature change. Temperature sensors have become highly sophisticated and versatile with electricity and modern electronics. Here are three types of temperature sensors:
● Thermocouples
As the name suggests, it uses two dissimilar metals coupling at the hot junction. The other end of the metals connects to the cold junction. When the hot junction exposes to temperature changes, it generates a voltage that can be detected using lead wires. The changes in voltage are proportional to the changes in temperature of the hot junction. Detecting the voltage provides temperature changes.
Thermocouples have various specifications that are relevant to specific applications and budget requirements. They can vary based on temperature, vibration resistance, durability, and chemical resistance. ANSI MC96.1 divides thermocouples into several types: J, K, T, E, R, S, and B.
Thermocouples are popular temperature sensors due to their higher temperature operating range, durability, and affordability.
● Resistance Temperature Detectors (RTD)
The RTD works by measuring the resistance of a wire exposed to temperature-changing conditions. It is a well-established science that changing the wire's temperature changes its resistance. As the temperature changes, the calibrated controller detects the change in resistance to provide a temperature value.
RTDs come in three configurations: 2, 3, and 4-Wire. Increasing the number of wires or wire thickness can lead to better accuracy, as the lead wire resistance can hinder the results of RTDs. The resistance wire can be made of different materials, resulting in various temperature ranges and accuracy.
● Semiconductor Temperature Sensors
Another popular type of temperature sensor is the semiconductor sensor. These sensors come in integrated circuits and are also called IC temperature sensors. When the temperature of the two diodes changes with the environment, a voltage change is created. A circuit detects the output and then converts it into a digital device signal.
These sensors are the most affordable and most widely adopted by the electronics industry. Computers, smartphones, data centers, and all other electronic hardware utilize these sensors to detect temperature changes. However, they are not ideal for high-temperature or very low-temperature applications. Their accuracy reduces drastically with temperature.
Working Principle of Humidity Sensors
Humidity sensors are widely used in the HVAC, food, and medical industries. Humidity can directly affect human comfort and, in the case of industrial motors, cause damage to the electrical conductors. Sensing and maintaining humidity is vital for process and environmental conditions. There are mainly three types of sensors:
● Capacitive Humidity Sensor
These sensors can detect humidity in the 0% to 100% (RH) range using the simple mechanism of measuring capacitance. A dielectric material separates two conductive materials. When the dielectric material is exposed to moisture or water molecules, its capacitance changes. The capacitance is directly proportional to relative humidity (%RH)
The sensor detects relative humidity by changing the capacitance value and is widely used in environmental monitoring and HVAC systems.
These capacitive humidity sensors have the fastest response time, less than a second. They can provide an accuracy of ±2% RH.
● Resistive Humidity Sensor
These are the most affordable types of humidity sensors. They use a hygroscopic material, such as salt, that absorbs atmospheric moisture. The hygroscopic material sits between the two conductors or electrodes. When the hygroscopic material absorbs moisture, its resistance increases, which the circuit detects to represent humidity in the air. A calibration curve (resistance vs. %RH) provides the relative humidity value against resistance.
● Thermodynamic Humidity Sensor
It is one of the more expensive types of humidity sensors, with a slow response time but high accuracy. They use a mirror surface that is cooled with temperature control. As the temperature starts decreasing, droplets begin to form on the mirror. The sensor detects this moment and registers the dew point temperature, which can translate into RH%.
Categories of Temperature and Humidity Sensors
Considering the different types of temperature and humidity sensors. We can divide them into five major categories:
- Standalone Temperature and Humidity Sensor: These sensors do not require any control systems. Batteries can power them and contain a display or analog with a pointer to indicate temperature and humidity.
- Infrared Temperature Sensor: Infrared temperature sensors are best for applications where the sensor cannot directly contact the solid or fluid. They are usually handheld and throw infrared light onto a surface, which bounces back into the detector on the handheld machine. The detector portion is also called a thermopile. The IR changes into heat and then into an electrical signal.
- Wireless Temperature and Humidity Sensor: This category is widely available for smart home applications. A central control unit gathers data from all the wireless temperature and humidity sensors and sends it to the user application. The user can then change settings such as HVAC, space heating, and water heating applications as per requirement.
- Analog Temperature and Humidity Sensor: These sensors are widely used in industrial and HVAC applications. They measure temperature and humidity changes with high accuracy to ensure that the process or production remains unaffected by these factors. They require a controller and wiring to operate.
- Digital Temperature and Humidity Sensor: These are usually IC or semiconductor sensors that generate output in 0 and 1. They are ideal for monitoring the temperature of silicon chipsets or other electronic hardware for feedback and protection shutdown signals. They have a low-temperature detection range, and their accuracy is only ideal for electronics applications.
Applications of Temperature and Humidity Sensors
Applications in HVAC Systems
Heating, ventilation, and air conditioning (HVAC) require multiple temperature and humidity sensors to make the environment suitable for humans, products, or processes. These sensors take real-time values to judge the conditions and adjust the HVAC system output accordingly.
To enhance the performance of your HVAC system, consider Alsavos' comprehensive range of products. Their product lineup includes thermostats, temperature sensors, humidity sensors, thermal actuators, thermostatic radiator valves, and other accessories. These products are suitable for residential, commercial, and industrial applications, providing solutions for optimizing HVAC system performance, improving energy efficiency, and enhancing comfort and control.
According to the OSHA Compliance for General Industry Manual, the ideal temperature range, also known as the “comfort zone,” lies between 22 °C to 27 °C and a relative humidity of 40% to 60%. HVAC systems adjust the environment through feedback from temperature and humidity sensors.
Applications in Industrial Settings
Using temperature and humidity sensors is inevitable in industrial applications such as medicine, warehouses, logistics, etc. In the warehouse, temperature and humidity are constantly monitored and adjusted to maintain the quality of the stored material and prevent damage. Similarly, product quality and chemical reactions can drastically change in medicine under different temperature and humidity ranges. Temperature and humidity sensors can be used on an industrial scale.
Applications in IoT Devices
IoT devices with wireless data transmission for user monitoring and control are ideal if you have a floor, water, or air cooling/heating system. They utilize the internet and WiFi to communicate and allow users to adjust temperature and humidity conditions. They play a vital role in smart homes. However, their recent implementation in agriculture and medical equipment has rapidly grown owing to their wireless nature. There are no wires, drastically reducing the cost of setting up such systems. Thermostats, temperature, and humidity sensors maintain target temperature and humidity.
How to Choose the Right Temperature and Humidity Sensor
Owing to the massive options of temperature and humidity sensors, finding the right one for your application can be challenging. Here are the simple aspects to look for in sensors to make an informed decision.
Applicability
Evaluate your requirements based on application. IoT devices are suitable for all applications where human comfort is involved. However, using detectors with high accuracy, durability, chemical resistance, and vibrational resistance are essential in industrial applications. Here is a table mentioning the suitable temperature and humidity sensors for various applications:
|
Application |
Temperature Sensor Type |
Humidity Sensor Type |
|
HVAC Systems |
Thermocouples, RTDs, Semiconductor Sensors |
Capacitive, Resistive, Thermodynamic |
|
Industrial Settings (e.g., food processing, pharmaceuticals) |
Thermocouples, RTDs, Semiconductor Sensors |
Capacitive, Resistive, Thermodynamic |
|
Data Centers, Server Rooms |
Semiconductor Sensors |
Capacitive |
|
Weather Stations |
Thermocouples, RTDs |
Capacitive, Resistive |
|
Healthcare Centers |
Semiconductor Sensors |
Capacitive, Resistive |
Accuracy and Resolution
Controlling temperature and humidity is critical to achieving the desired results in industrial and scientific applications. The accuracy and resolution can vary depending on the type of sensor. Here is a table representing the accuracy and resolution of different types of humidity and temperature sensors. Consider these factors based on your requirements.
|
Type |
Accuracy |
Resolution |
|
Thermocouple |
±0.1°C to ±1°C |
0.01°C to 0.1°C |
|
Resistance Temperature Detector (RTD) |
±0.1°C to ±0.5°C |
0.01°C to 0.1°C |
|
Semiconductor Temperature Sensor |
±0.5°C to ±1°C |
0.1°C |
|
Capacitive Humidity Sensor |
±1% RH to ±3% RH |
0.1% RH to 0.5% RH |
|
Resistive Humidity Sensor |
±2% RH to ±5% RH |
0.1% RH to 1% RH |
|
Thermodynamic Humidity Sensor |
±0.5% RH |
0.1% RH |
Response Time
Response time is the time the sensor requires to reach a stable value in line with the environment. The response time in domestic applications does not need to be high. Meanwhile, a high-response sensor is critical in industrial applications to allow the system to adjust parameters as quickly as possible. Here are the general response times of sensors:
- Thermocouple: Fast (seconds to minutes)
- Resistance Temperature Detector (RTD): Fast (seconds to minutes)
- Semiconductor Temperature Sensor: Very fast (milliseconds)
- Capacitive Humidity Sensor: Fast (seconds)
- Resistive Humidity Sensor: Slow (minutes)
- Thermodynamic Humidity Sensor: Slow (minutes)
Durability and Environmental Suitability
Equipment must be durable in a highly corrosive, chemical, humid, temperature, vibration, and dusty environment. A user considering buying a temperature and humidity sensor should have an in-depth look at the following factors before making the purchase:
- Chemical Compatibility
- Resistance to Corrosion
- Temperature Tolerance Range
- Vibration Resistance
- Dust Resistance
- IP Rating
- Humidity Tolerance
- Outdoor Use
Future Developments and Technological Trends
Advances in Sensor Technology
The world is advancing in every field, and owing to massive industrialization, innovation in sensor technology is inevitable. In the future, sensors will have higher accuracy, resolution, and an ultra-low response time. Material technology will allow sensors to operate in extreme conditions without damage. WiFi and 4G are currently implemented in IoT devices for smart homes. Their maturity and expected 5G integration will soon make their reporting ultra-fast.
Sustainability and Energy Efficiency
HVAC systems were the most significant contributors to greenhouse gases, but scientists immediately found the problem of replacing refrigerants with ozone-friendly gases. Similarly, advanced inverter technology and precise sensors improve temperature control and higher efficiency. Modern HVAC systems consume less power and provide more comfort. The food processing industry, power plants, and weather stations are becoming more efficient in detection, leading to better process efficiency and output.
FAQ
- How accurate are temperature and humidity sensors in extreme conditions?
A thermocouple types sensor can provide accuracy of ±0.5°C to ±1°C (for temperatures between -200°C and 1300°C). However, it has slow response time. In comparison, RTDs can provide ±1°C to ±2°C (for temperatures between -200°C and 850°C) accuracy. There can always be exceptions to these ranges, but they are specialized sensors that usually have premium price tags.
- Can a single sensor monitor both temperature and humidity?
Yes, sensors for industrial and domestic use can detect temperature and humidity together. For industrial use, the purpose is to provide space-saving extra ports in process piping or ducts, whereas in home applications, it saves on costs and installation hassle. Their accuracy and range may not be as robust as those of industrial-dedicated sensors.
- How often do temperature and humidity sensors need calibration?
In industrial applications, these sensors are calibrated using preventive maintenance plans, which are usually set at an annual frequency. Sensor material and wiring characteristics can change over time, affecting the calibration curve. The controller must adjust to the change for an accurate reading at least once a year.
- What’s the difference between analog and digital temperature sensors?
Analog sensors sense the temperature change and provide an analog output, while digital temperature sensors provide a digital output. However, the production of an analog sensor can be a change in voltage or resistance across the sensor. Similarly, digital sensors provide output in 0s and 1s that is detectable by digital circuits.
- How do temperature and humidity sensors help optimize HVAC efficiency?
HVAC systems need feedback on temperature and humidity from actual conditions to adjust their settings. Modern HVAC systems come with inverter-based compressors that can change their speed to adjust cooling requirements generated by temperature and humidity sensors. This leads to lower temperature fluctuations with lower power consumption during operation.
