There are two types of temperature and humidity sensor, contact and non-contact, according to the monitoring method.
Contact:The detection part of the contact temperature sensor has good contact with the measured object, also known as thermometer. The thermometer achieves thermal equilibrium by conduction or convection, so that the indicated value of the thermometer can directly represent the temperature of the measured object. Generally the measurement accuracy is high.
Within a certain temperature measurement range, thermometers can also measure the temperature distribution inside the object. But for the moving body, small target or heat capacity of the object is very small will produce a large measurement error, commonly used thermometers are bimetallic thermometers, glass liquid thermometers, pressure thermometers, resistance thermometers, thermistors and temperature difference thermocouples and so on.
Non-contact: Its sensitive element and the object to be measured do not contact each other, also known as non-contact temperature measurement instrument. This type of instrumentation can be used to measure the surface temperature of moving objects, small targets and objects with a small heat capacity or rapid temperature change (transient), as well as to measure the temperature distribution of a temperature field.
The most commonly used non-contact thermometry instruments are based on the fundamental law of blackbody radiation and are called radiometric thermometry instruments. Radiometric methods include luminance (see optical pyrometer), radiation (see radiation pyrometer) and colourimetric (see colourimetric thermometer). Each type of radiometric thermometry can only measure the corresponding photometric, radiometric or colourimetric temperature.
The temperature sensing element can be classified into three categories: platinum RTD temperature sensors, thermocouple temperature sensors, and thermistor temperature sensors.
1.Platinum RTD temperature sensor
Platinum RTD is the use of platinum wire resistance value with the change of temperature and the change of this basic principle of design and production, according to the 0 ℃ resistance value R (℃) size is divided into 10 Ohm. (graduation number for Pt10) and 100 ohms (graduation number for Pt100), etc., the temperature measurement range are -200 ~ 850 ℃.
The use of PT100 platinum RTD as a temperature sensing element models are armoured, assembled, socketed, end face RTDs. The measurable range is from -200 degrees Celsius to 150 degrees Celsius and -50 degrees Celsius to 850 degrees Celsius. Mainly used in industries that require small temperature error or precision instrumentation.
2.Thermocouple temperature sensor
Thermocouple temperature sensor is mainly through two different metal materials welded together, the main temperature change, then there will be different potential generated at both ends, through the potential change to derive the corresponding temperature change.
Measurable temperature: up to 2300 degrees, in the high-temperature section of the more accurate use of the K-type positive level.
3.Thermistor
Composed of metal oxide ceramics, is a low-cost, highest sensitivity temperature sensor.
Temperature measurement range: small temperature range -50 to about 200 degrees, small size, fast response time. Because of the low price so in many household appliances are used.
The main purpose of the temperature sensor:
Temperature is a physical quantity that reflects the degree of heat and cold of an object, and is an important and common measurement parameter in the process of industrial and agricultural production. Temperature measurement and control in ensuring product quality, improve production efficiency, energy saving, safe production, and promote the development of the national economy plays a very important role.
Due to the ubiquity of temperature measurement, temperature sensors rank first among all kinds of sensors, accounting for about 50 per cent. Temperature sensors measure temperature indirectly by changing certain properties of an object. The properties of many materials and components change with temperature, so there is a considerable number of materials that can be used as temperature sensors.
Temperature sensors vary with temperature in physical parameters such as expansion, resistance, capacitance, electric potential, magnetism, frequency, optical properties and thermal noise. New temperature sensors will continue to emerge as production evolves.