When choosing a humidity sensor, you must first figure out what kind of humidity sensor you need; your financial resources allow you to buy what grades of products, and weigh the relationship between “need and possible†and not blindly. From the interaction with users, we feel that the following issues are worth noting.
1. Select the measurement range and measure the weight and temperature. Select the humidity sensor first to determine the measurement range. In addition to meteorological and scientific research departments, temperature and humidity measurement and control generally do not require full wet range (0-100% RH) measurement. In today's information age, sensor technology is closely integrated with computer technology and automatic control. The purpose of the measurement is to control, the measurement range and the control range are collectively used. Of course, for those who do not need to engage in measurement and control systems, it is ok to directly select a universal hygrometer. The following is a list of the different requirements for the temperature and humidity of the humidity sensor in some application areas for the user's reference (see Table 1). The user proposes the measurement range to the sensor manufacturer according to the needs. The manufacturer gives priority to ensuring that the performance of the sensor is stable and consistent within the scope of use, and obtaining a reasonable performance-price ratio is a mutually beneficial thing for both parties.
2. The measurement accuracy is the same as the measurement range. The measurement accuracy is the most important indicator of the sensor. Every increase is a percentage point. For the sensor, it is the last step, even the previous level. Because of the different precisions, the manufacturing costs vary widely, and the selling price is far from the same. For example, an imported low-cost humidity sensor is only a few dollars, and a full-wet humidity sensor for calibration is several hundred dollars, a difference of nearly a hundred times. Therefore, users must tailor their clothes, and they should not blindly pursue "high, precise, and sharp." Manufacturers often give the accuracy of their humidity sensors in sections. For example, the medium and low temperature sections (0-80% RH) are ±2% RH, while the high-humidity section (80-100% RH) is ±4% RH. And this accuracy is the value at a given temperature (eg 25 ° C). For example, use a humidity sensor at different temperatures. The indications also take into account the effects of temperature drift. It is well known that relative humidity is a function of temperature, which severely affects the relative humidity within a given space. The temperature changes by 0.1 °C. A humidity change (error) of 0.5% RH will be produced. In the case of use, if it is difficult to achieve constant temperature, it is not appropriate to propose excessive humidity measurement accuracy. Because the humidity is also erratic with temperature changes, the luxury measurement accuracy will lose its practical significance. Therefore, the first thing to control the humidity is to control the temperature. This is why a large number of applications are often temperature and humidity-body sensors rather than just humidity sensors.
In most cases, the accuracy of ±5% RH is sufficient if there is no precise temperature control or if the space being tested is unsealed. For areas requiring precise control of constant temperature, constant humidity, or where it is necessary to track and record humidity changes at any time, select a humidity sensor with an accuracy of ±3% RH or higher. The temperature sensor corresponding to this should have a temperature measurement accuracy of ±0.3 ° C or more, at least ± 0.5 ° C. The requirement that the accuracy is higher than ±2% RH may be difficult to achieve even the standard humidity generator of the calibration sensor, not to mention the sensor itself. According to the article in the humidity room of the National Standards Research Center, "The relative humidity measurement instrument, even at 20-25 ° C, is still difficult to achieve 2% RH accuracy."
Field department temperature (°C) humidity (%RH)
Textile spinning mill 2360
Weaving factory 1885
Pharmaceutical pharmaceutical factory 10 ~ 3050 ~ 60
Operating room 23 ~ 2650 ~ 60
Light Industry Printing Factory 23～2749～51
Cigarette factory 21 ~ 2455 ~ 65
Match factory 18~2250
Electronic semiconductor 2230～45
Computer room 20～3040～70
Communication cable inflation -10 ~ 300 ~ 20
Food beer fermentation 4 ~ 850 ~ 70
Breeding of agricultural varieties 15~4040～75
Artificial greenhouse 5～4040～100
Warehousing fruit freezing -3 ~ 580 ~ 90
Underground dish 窖-3～ -170～ 80
Cultural relics storage 16～1850～55
3, consider time drift and warm drift
Almost all sensors have drift and temperature drift. Since the humidity sensor must be in contact with moisture in the atmosphere, it cannot be sealed. This determines its stability and longevity is limited. Under normal circumstances, the manufacturer will indicate that the effective use time of one calibration is 1 year or 2 years, and it is responsible for recalibration due to expiration. Users should consider the channels for recalibration in the future when selecting sensors. Do not greet cheap or superstitious foreign goods and ignore the after-sales service.
The temperature drift has been mentioned in the last section. Select the humidity sensor to consider the temperature range of the application, to see if the selected sensor can work normally at the specified temperature, and whether the temperature drift exceeds the design specifications. The user should be reminded that the temperature coefficient α of the capacitive humidity sensor is a variable, which varies with the temperature and humidity range. This is because the dielectric constant of water and polymer is not synchronized with the change of temperature, and the temperature coefficient α depends mainly on the dielectric coefficient of water and the moisture sensitive material, so the temperature coefficient of the capacitive humidity sensor is Very few. The capacitive humidity sensor has the lowest temperature coefficient in the normal temperature and the medium wet section, and the temperature drift in the middle and low humidity sections is negligible at 5-25 °C. However, when used in high temperature and high humidity areas or negative temperature and high humidity areas, it is necessary to consider the effects of temperature drift and make necessary compensation or correction.
Product Name: Car Charger
Place of Origin: Guangdong, China (Mainland)
Brand Name: OEM
Output Type: DC
Connection: Other
Rated Voltage: 12V-24V
Working Temp: 0-55℃
Weight: 36g
Materials: PC+ABS
Color: White Black
Warranty: 1 year
Suitable for:Most digital devices
SMART PROTECTION & ATTRACTIVE DESIGN ------ Intelligent circuit design protects against short circuiting,over-heating,over-current,and over-charging. Charging stops when battery is full. Car charger with blue LED indicator,which makes it convenient to find exactly where the connection should go; And the light is soft enough not to distract at night.
Dual USB Car Charger Adapter,USB Smart Port Charger ,Car Charger,USB Car Charger For Phone
Shenzhen Waweis Technology Co., Ltd. , https://www.waweispowerasdapter.com