How to chooseand humidity sensor
How to choose Humidity sensor With thedevelopment, research, agricultural, HVAC, textile, machine room,aerospace, power and other industrial sectors, a growing need toadopt Humidity sensor, the product of higher quality requirementsmore industry, the environmental temperature , humidity control andthe value of industrial materials, monitoring and analysis of waterhave become one of the more common technical requirements. Humiditysensor and humidity measurement products, 90 belong to the rise ofthe industry. How to use a good Humidity sensor, how to determinethe Humidity sensor performance, which is the average user isconcerned, is still a more complex technical issues. The followingarticle for your reference. First, the Humidity sensor humiditysensitive characteristics of the classification and Humiditysensor, resistive and capacitive divided into two types, the basicform of the product are coated in the substrate material to form asense of being wet wet film. Adsorption of water vapor in the airin the sense of the wet material, device impedance, dielectricconstant change a lot, which made humidity sensor. Domestic andforeign manufacturers of the Humidity sensor products, differentlevels, quality and price are different, the user how to choose theideal product for the best cost performance certainly has somedifficulty in this respect in-depth understanding. Humidity sensorhas the following characteristics: 1, accuracy and long-termstability of the Humidity sensor accuracy should reach ± 2% ~ ± 5%RH, very difficult to reach this level as the use of measuringinstruments, Humidity sensor to achieve ± 2% ~ ± 3 % RH accuracy ismore difficult, and often feature product information is given atroom temperature (20 ℃ ± 10 ℃) and the clean gas measurement. Inactual use, due to dust, the impact of oil pollution and harmfulgases, the use over time, will produce aging, decreased accuracy,Humidity sensor's accuracy level is combined with its long-termstability to judge, in general, and the use of long-term stabilityLife is the impact of Humidity sensor first-class quality problems,the annual shift of control in 1% RH level products rarely,generally in the ± 2% or so, or even higher. 2, the Humiditysensor's temperature coefficient of humidity sensor in addition tohumidity-sensitive, but also very sensitive to temperature, thetemperature coefficient is generally in the 0.2 ~ 0.8% RH / ℃range, and in some cases the relative humidity sensor at differenthumidity , there are differences between the temperaturecoefficient. Nonlinear drift, which needs to increase thetemperature compensating circuit. Using SCM software compensation,with or without temperature compensation of the Humidity sensor isnot guarantee the accuracy of the whole temperature range, Humiditysensor drift and the linear compensation of a direct impact on theeffect of nonlinear temperature drift compensation is often notgood results, only the use of hardware temperature compensationwill be granted following the true nature of the compensationeffect. Humidity sensor working temperature range is also importantparameters. Most humidity sensor is difficult to work in more than40 ℃. 3, the Humidity sensor in the supply of metal oxide ceramics,polymers and lithium chloride humidity sensitive materials such asDC voltage is applied, it will lead to performance changes, or evenfailure, so this type of Humidity sensor can not use DC voltage orDC component AC voltage. Must be the AC power supply. 4,interchangeability present, Humidity sensor interchangeabilitywidespread phenomenon of the poor, the same type of sensors are notinterchangeable, seriously affected the results, to themaintenance, testing increased the difficulty, some manufacturershave made in this respect the efforts (but still very poorinterchangeability) achieved good results. 5, humidity, temperaturecorrection calibration and humidity much more difficult thancorrected. Temperature calibration is often used as a standard to astandard thermometer, and humidity calibration standards difficultto achieve, wet and dry bulb thermometer and hygrometer some commonpointer is not used for calibration, the accuracy can not beguaranteed, because the Environment conditions are very strict, ingeneral, (the best fit in the humidity conditions) in the absenceof complete test equipment, usually saturated salt solution with asimple test method, and measure its temperature. Second, to theHumidity sensor performance for several methods to determine theinitial Humidity sensor calibration difficulties in practicalcases, the method by some simple Humidity sensor to determine theperformance and inspection. 1, the consistency determination, thesame type, same manufacturer of Humidity sensor products, the besttime to buy two or more, the more illustrative, comparative testingtogether power output value, in the relatively stable conditions,the observation of the consistency test . If further testing can berecorded in the 24h time to time the inner room, generally within aday of high, medium, low humidity and temperature conditions 3, youcan observe a more comprehensive product consistency and stability,including temperature compensation. 2, mouth Oh wet gas or usingother means of humidity sensors to observe the sensitivity,reproducibility or drying wet performance, and resolution, thehighest range of products and so on. 3, open boxes and relatedproducts for both cases, the test box. Comparison is consistent, toobserve the thermal effect situation. 4 products in hightemperature and low temperature (according to the instructionsstandard) test, and returned to normal before the next inspectionand test records for comparison, examine the product's temperatureadaptation, and observe the consistency of the product situation.Based on the performance of the final product quality inspectiondepartments to complete the formal means of detection. Saturatedsalt solution used for calibration, can also use the brand-nameproducts for comparison testing, the product should be in theprocess of long-term use of a more comprehensive long-termcalibration to determine the Humidity sensor's quality. Third, themarket Humidity sensor products, some of the domestic market, therewere many foreign Humidity sensor products, is common in capacitivehumidity sensor, a sense of the main types of wet polymer material,lithium chloride and metal oxide. Capacitive humidity sensor hasthe advantage of fast response, small size, linearity, more stable,also has some foreign products, high temperature performance.However, the performance of the products to achieve the above andmore for foreign brands, prices are more expensive. The market tosell some of the capacitive humidity sensor low-priced products,often reach the level of linearity, consistency and repeatabilityare not that good, 30% RH less, 80% RH over the wet section ofdeformed sense. Some products using SCM compensation correction, sohumidity is a "step" of the jump, the accuracy decreased, thereconsistency is poor, the shortcomings of linear difference. Whetherhigh-end or low end of the capacitive humidity sensor, long-termstability is not ideal, the majority of serious long-term use ofdrift, as the humidity changes in capacitance values of pF-level,1% RH change of less than 0.5pF, capacitance drift Gaibian oftencaused the error scores of RH%, the majority do not have thecapacitive humidity sensor temperature of 40 ℃ above theperformance of the work, often fail and damage. Capacitive humiditysensor is also more a lack of corrosion resistance, often require ahigher cleanliness of the environment, and some products are stilllight failure, such as the failure phenomenon of staticelectricity, metal oxide ceramic humidity resistance, capacitancewith the same humidity merits, the dust environment, the ceramiccomponents will fail pore is blocked, often by removal of the waysto deal with power, but the effect is not ideal, and can not beused in explosive environments, alumina can not overcome a sense ofwet materials The surface structure of "natural aging" weakness,impedance instability, humidity resistance of metal oxide ceramicmaterials are also weaknesses in poor long-term stability there.Lithium chloride humidity resistance, with the most prominentadvantage of strong long-term stability, so by strict productionprocess, instrumentation and sensors made products can achieve highaccuracy, strong stability is a product with good linearity ,precision and consistency, a reliable long-term life assurance.Lithium chloride humidity sensor humidity sensitive materials,other long-term stability could not be replaced.