【 Weak current College 】 how to choose the humidity sensors determine humidity sensor performance-Power By 【 China power house network 】

With the development of the times, research, agriculture, HVAC, textile, machinery room, aerospace, electric power and other industrial sectors, increasing need humidity sensor, the product quality requirements, industry, environmental temperature and humidity control, as well as industrial material moisture value of monitoring and analysis have become more common technical specifications. Humidity sensor products and humidity measurement is the rise of industry in the 90s. How to use good humidity sensor, how to judge the humidity sensor performance, the average user, there is a more complex technical issues.
Following this text for your reference.

First, the classification and the humidity sensor humidity characteristics
　　
Humidity sensor, is divided into two kinds of resistive and capacitive, the basic form of the product are in the substrate coated with wet materials are wet film formation. Air humidity absorption of water vapor in the materials, components of impedance, media, constant great changes occurred, thus made of humidity sensor.
Domestic manufacturers of humidity sensor product levels, different quality price, users how to select an optimal price-performance ideal product does have a certain degree of difficulty, needs to be made in this regard. Humidity sensor has the following characteristics:

1. accuracy and long-term stability
　　
Humidity sensor accuracy should meet ± 2% ~ ±5% RH, not reach this level is very difficult to use as measuring instruments, humidity sensor to meet ± 2% ~ ±1% RH precision is difficult, usually given in the product information of the characteristics is at room temperature (20 ° c ± 10 ° c) and clean gas measurement. In actual use, due to dust, oil and harmful gases, use over time, will produce a decline in ageing, precision, accuracy level of humidity sensor with its long-term stability to determine, in General, long-term stability and useful life is a top quality humidity sensor, volume control, drift in 1% RH level of products rarely, usually in ± 2% or even higher.

2. humidity sensor temperature coefficient
　　
Humidity sensor in addition to ambient humidity sensitive, very sensitive to temperature, the temperature factor generally 0.2 ~ 0.8% RH/° c, and the humidity sensor under the different relative humidity, temperature coefficient differentiated. Drift nonlinear, it needs in circuit plus temperature compensated. Using SCM software compensation, or without temperature compensation of humidity sensor is can not guarantee the accuracy of the full range of temperature, humidity sensor drift linearization curve directly affect compensation effect, often linear temperature drift compensation not better results, only use hardware temperature follow of compensation will be real compensation effects. Humidity sensor working temperature range is also an important parameter. Most humidity sensor to 40 ° c above normal.

3. humidity sensor power supply
　　
Metal oxide ceramic, polymer and lithium chloride, humidity sensitive materials imposed DC voltage, can cause performance changes, or even failure, so this type of humidity sensor cannot use DC voltage or AC voltage DC components. Must be AC power supply.

4. interchangeability
　　
At present, the humidity sensor prevailing interchangeability of phenomena, the same models of sensors are not interchangeable, seriously affecting the use of results, to repair, debugging, increased difficulties, some manufacturers in this context efforts, (but the interchangeability is still very poor) achieved good results.

5. humidity correction

Calibration of temperature and humidity than correction is much more difficult. Temperature calibration is often a standard thermometer for standard, but humidity calibration standards more difficult to achieve, wet and dry bulb thermometers and some common analog hygrometer is not used as a calibration, accuracy cannot beguaranteed, because it requires very strict environmental conditions, General conditions (preferably in humidity environment fit) in the absence of complete verification device, usually with a simple method of calibrating the saturated salt solutions, and measure its temperature.

Second, on humidity sensor performance for preliminary judgment of

Actual in humidity sensor calibration difficult situations, you can make some easy way to judge and humidity sensor performance.

1. consistency of the judgment, of the same type, the same manufacturers of humidity sensor product is the best time to buy two or more, more, put together power comparison test output values, in a relatively stable conditions, observe the consistency. If further testing, a section within the interval 24h time records, a day usually has high, medium, low humidity and temperature 3 kind, can comprehensively study product uniformity and stability, including temperature compensation feature.

2, with mouth gas or use other wow humidification means on sensor wetting, observation of their sensitivity and repeatability, rising damp dehydration performance, as well as the resolution, the maximum range of products, etc.

3. on the product as open cartridge and close the box of the test. A comparison is consistent, the observation of the thermal situation.

4. on the product in high temperature and low temperature (depending on the specification of criteria) and back to their normal state detection and the record before the experiment to compare the test product temperature adaptability and observe the consistency of the product.
Product performance final quality inspection departments to be based on regular complete detection means. Use of saturated salt solutions for calibration, brand-name products can also be used for comparison testing, product should conduct long-term use of long-term calibration to more comprehensive judgment humidity sensor quality.

3. on the market some humidity sensor product analysis
　　
Domestic market a lot of humidity sensor products at home and abroad, capacitive humidity sensor, comparatively see more species are wet materials, mainly for high polymer, lithium and metal oxides.
　　
Capacitive humidity sensing elementOne advantage is that response speed, small size, linearity, more stable, foreign some products also have high-temperature performance. But the performance of the product for the overseas famous brand, prices are more expensive. The market sold some capacitive humidity sensor low-priced products, often do not meet these standards, linearity, consistency and repeatability are not satisfactory, 30% RH to 80% RH, humidity above paragraph deformation. Some products using microcomputer compensation correction, the humidity with a "step" of jump, the loss of precision, consistency, linear differential weakness. Whether high-or low-quality capacitive humidity sensor, long term stability are not satisfactory, the most serious long-term drift, humidity capacitance tolerance values change as the pF, 1% RH deficiency of change, capacity value 0.5pF drift change often caused dozens of RH% error, most capacitive humidity sensor does not have more than 40 ° c temperatures often failure of performance, and damage.
　　
Capacitive humidity sensor corrosion resistance is relatively short, often on environment cleanliness requirements are high, some products also have lighting failure, failure phenomena such as static electricity, metal oxide varistor for ceramic wet, with humidity capacitance of the same advantages, but dust environment, ceramic fine-pored will be plugging components, often using power dust removal to deal with, but the effect is not ideal, and flammable and explosive environments can not be used, aluminium oxide humidity material could not overcome its surface structure "natural aging" weaknesses, impedance, metal oxides ceramic humidity resistance there isalso the weakness of the long-term stability of difference.
　　
Lithium chloride, humidity resistance has the most significant advantage is the extremely strong long-term stability, through a rigorous process, made of instrument and sensor products can achieve high precision, stable is a product with good linearity, accuracy and consistency, a long-term service life of a reliable guarantee. Licl humidity sensor humidity long term stability of other materials are irreplaceable.