On the difference between humidity sensor and humidity transmitter

Temperature and humidity transmitter is a kind of transmitter device equipped with humidity sensitive and temperature sensing elements, which can be used to measure temperature and humidity and display them Due to its small size, stable performance and high precision, temperature and humidity transmitter is widely used in various fields of production and life Temperature and humidity sensor refers to the equipment or device that can convert temperature and humidity into electrical signals that are easy to be measured and processed There is no display function 1 The function of the temperature and humidity transmitter is to change the electrical signal transmitted by the temperature and humidity sensor into 0-5V voltage or 4-20mA industrial control current signal 2 Classification and characteristics of the humidity sensor 1 Classification of the humidity sensor The humidity sensor is divided into resistance type and capacitance type The basic form of the product is to form the humidity sensing film by coating the humidity sensing material on the substrate After the water vapor in the air is adsorbed on the humidity sensing material, the impedance and medium constant of the element change greatly, so that the humidity sensing element is made 2 Characteristics of humidity sensor: the level of humidity sensor products of various manufacturers at home and abroad is different, and the quality and price are quite different How to choose the ideal product with better performance and price than Zui is really difficult, which needs to be understood in depth The humidity sensor has the following characteristics: (1) accuracy and long-term stability The accuracy of the humidity sensor should reach ± 2% ～± 5% RH, which is difficult to be used as a measuring instrument It is difficult for the humidity sensor to reach ± 2% ～± 3% RH Generally, the characteristics given in the product data are measured in normal temperature (20 ℃ ± 10 ℃) and clean gas In practical use, due to the influence of dust, oil pollution and harmful gases, aging will occur and accuracy will decline after a long time of use The accuracy level of humidity sensor should be judged in combination with its long-term stability Generally speaking, long-term stability and service life are the first problems affecting the quality of humidity sensor There are few products with annual drift controlled at 1% RH level, generally ± 2 %Left and right, even higher (2) humidity sensor's temperature coefficient humidity sensor is very sensitive to not only the environment humidity, but also the temperature Its temperature coefficient is generally in the range of 0.2 ~ 0.8% RH / ℃, and some humidity sensors have different temperature coefficient under different relative humidity Temperature drift is non-linear, which requires temperature compensation on the circuit The accuracy of the whole temperature range can not be guaranteed by using the single chip microcomputer software compensation or the humidity sensor without temperature compensation The linearization of the temperature drift curve of the humidity sensor directly affects the compensation effect The non-linear temperature drift usually can not be compensated well Only the hardware temperature follow-up compensation can obtain the real compensation effect The temperature range of humidity sensor is also an important parameter Most humidity sensors are difficult to work normally above 40 ℃ (3) when DC voltage is applied to the power supply of humidity sensor, such as metal oxide ceramic, polymer, lithium chloride and other humidity sensitive materials, the performance will change or even fail, so this kind of humidity sensor cannot use DC voltage or AC voltage with DC component It must be AC powered (4) interchangeability at present, the phenomenon of poor interchangeability is common in humidity sensor The same type of sensor can not be interchanged, which seriously affects the use effect, and increases the difficulty of maintenance and debugging Some manufacturers have made various efforts in this respect, but the interchangeability is still very poor, which has achieved good results (5) humidity correction humidity is much more difficult than temperature correction A standard thermometer is often used as the standard for temperature calibration, but the humidity calibration standard is difficult to achieve The dry and wet bulb thermometer and some common pointer type hygrometers cannot be used for calibration, and the accuracy cannot be guaranteed, because they require very strict environmental conditions Generally, (Zui is better under the conditions suitable for humidity environment) in the absence of perfect calibration equipment, they are usually used A simple method for the determination of saturated salt solution and the measurement of its temperature 3 Several methods to make a preliminary judgment on the performance of the humidity sensor In the case that the actual calibration of the humidity sensor is difficult, some simple methods can be used to judge and check the performance of the humidity sensor (1) consistency judgment: for the same type and the same manufacturer's humidity sensor products Zui, it is better to buy more than two at a time, the more the problem is, put them together to power on and compare the test output value, and observe the test consistency under relatively stable conditions If further testing is carried out, it can be recorded in a period of time within 24 hours Generally, there are three kinds of humidity and temperature conditions of high, medium and low in a day The consistency and stability of the product can be observed comprehensively, including temperature compensation characteristics (2) humidify the sensor with wet towel or other humidification means, and observe the characteristics, sensitivity, repeatability, dehumidification performance, resolution, Zui high range of the product under the condensation state (3) test the product at high temperature and low temperature (according to the specification standard), and compare the test and the record before the test when it returns to normal state, check the temperature adaptability of the product, and observe the consistency of the product The performance of Zui products must be based on the formal and complete testing methods of the quality inspection department In order to judge the quality of the humidity sensor comprehensively, the saturated salt solution can be used for calibration, and the product can also be used for comparison test In short, the longer people use humidity sensors, the deeper and more comprehensive understanding At the same time, it also puts forward new requirements for the product, which brings new opportunities to the product and promotes the technology to a new height We believe that humidity sensor products will play an increasingly important role in the application field 3、 Difference between humidity sensor and humidity transmitter humidity sensor in narrow sense refers to humidity sensitive devices, now generally refers to various humidity sensor components or circuit boards that can not be directly used in the field Generally, its output is not standard 0 ~ 5V or 4 ~ 20mA signal, and there is no power protection, filtering and other field necessary peripheral circuits, and there is no direct use of wall mounted or pipeline type packaging forms In traditional sense, humidity transmitter refers to 0 ~ 5V, 0 ~ 10V or 4 ~ 20mA output humidity sensor Now it generally refers to a variety of humidity sensor products that can be directly used in the field In practical use, the two concepts are not very clear, often referred to as humidity sensor However, there are still great differences in practical application Humidity sensor only ensures the accuracy of sensor probe The comprehensive accuracy of Zui terminal is not only related to the principle design of peripheral circuit, but also related to the welding process of peripheral circuit The humidity transmitter guarantees the comprehensive accuracy of Zui terminal (including peripheral circuit), and gives the test data without correction Therefore, it is convenient for users to use humidity transmitter.