In addition to electrical signals, the signals people use daily are optical signals. But in fact, temperature and humidity can also send out signals. The device that receives temperature and humidity signals is a temperature and humidity sensor. People use temperature sensors to make many supplies. The most common one is the thermometer, which is the simplest kind of temperature sensor. Temperature sensors are also divided into two types, one requires contact with substances and is called a contact sensor, while the other does not require contact because it has a sensitive element. Let’s teach you how to choose a temperature and humidity sensor.
Introduction to temperature and humidity sensors
Temperature sensor (temperature? transducer) refers to a sensor that can sense temperature and convert it into a usable output signal. Temperature sensors are the core part of temperature measurement instruments and come in many varieties. According to the measurement method, it can be divided into two categories: contact type and non-contact type. According to the characteristics of sensor materials and electronic components, it can be divided into two categories: thermal resistance and thermocouple.
Method for selecting temperature sensors
1. Thermocouple
Thermocouple is the most commonly used temperature sensor in temperature measurement. Its main advantages are wide temperature range and adaptability to various atmospheric environments. It is also sturdy and low-priced. It does not require power supply and is also the cheapest. A thermocouple consists of two different metal wires (metal A and metal B) connected at one end. When one end of the thermocouple is heated, there is a potential difference in the thermocouple circuit. The measured potential difference can be used to calculate the temperature.
However, there is a non-linear relationship between voltage and temperature. Since voltage and temperature are non-linear, temperature needs to be measured a second time for the reference temperature (Tref), and the test equipment software or hardware is used to measure the temperature inside the instrument. The voltage-temperature conversion is processed to ultimately obtain the thermocouple temperature (Tx). The Agilent 34970A and 34980A data loggers have built-in measurement computing capabilities.
In short, thermocouples are the simplest and most versatile temperature sensors, but thermocouples are not suitable for high-precision measurements and applications.
2. Thermistor
Thermistor is made of semiconductor material, most of which have negative temperature coefficient, that is, the resistance decreases as the temperature increases.
Temperature changes will cause large resistance changes, so it is the most sensitive temperature sensor. However, the linearity of the thermistor is extremely poor and has a lot to do with the production process. The manufacturer cannot give a standardized thermistor curve.
The thermistor is very small and responds quickly to temperature changes. But the thermistor requires a current source, and its small size also makes it extremely sensitive to self-heating errors.
The thermistor measures absolute temperature on two lines and has better accuracy, but it is more expensive than a thermocouple, and its measurable temperature range is smaller than a thermocouple. A commonly used thermistor has a resistance of 5kΩ at 25°C, and every 1°C temperature change causes a resistance change of 200Ω. Note that the 10Ω lead resistance only causes a negligible 0.05°C error. It is ideally suited for current control applications requiring fast and sensitive temperature measurements. The small size is advantageous for applications with space requirements, but care must be taken to prevent self-heating errors.
This is the introduction to the temperature and humidity sensor method. I believe everyone has a certain understanding of it. In fact, the most important thing is not the selection of the temperature sensor, but what everyone should know about the device. Principles and correct usage methods to make it better serve people. Moreover, people will choose what kind of temperature sensor to use based on their own needs. Technology is still developing. I believe that the application of sensors will gradually increase, and more related substances will be invented to work for people.