Humidity sensor procurement guide

1. Select the measurement range and measure the weight, temperature, select the humidity sensor first to determine the measurement range. In addition to the meteorological and scientific research departments, the measurement of temperature and humidity generally does not require a full-scale wet process (0-100% RH) measurement. In today's information age, sensor technology is closely linked with computer technology and automatic control technology. The purpose of the measurement is to control, and the measurement range and control range are collectively called the range of use. Of course, for those who do not need to implement a measurement and control system, the direct selection of a universal hygrometer is all that is required. Here are some of the different requirements for humidity sensor temperature and humidity in some application areas for users' reference (see Table 1). The user provides measurement scope to the sensor manufacturer according to the needs. The manufacturer gives priority to ensure that the user's performance is stable and consistent within the use range, and obtaining a reasonable performance-cost ratio is a matter of mutual benefit for both parties.

2. Select the same measurement accuracy as the measurement range. The measurement accuracy is the most important indicator of the sensor. Each increase - a percentage point. For the sensor is the previous step, or even the previous level. Because to achieve different accuracy, the manufacturing costs vary greatly, and the price difference is very far. For example, an imported low-cost humidity sensor is only a few dollars, and a full-humidity humidity sensor for calibration is several hundred dollars, a difference of nearly 100 times. Therefore, users must tailor their clothing to avoid blindly pursuing “high, fine, sharp”.

Manufacturers often segment the accuracy of their humidity sensors. For example, the middle and low temperature (0-80%RH) is ±2%RH, while the high humidity (80-100%RH) is ±4%RH. And this accuracy is a value at a specified temperature (eg, 25°C). If the humidity sensor is used at different temperatures, its indication must also consider the effect of temperature drift. As we all know, relative humidity is a function of temperature, and the temperature affects the relative humidity in a given space. Each temperature changes by 0.1°C. A humidity change (error) of 0.5% RH will be generated. If it is difficult to use a constant temperature in the occasion of use, it is not suitable to propose excessively high humidity measurement accuracy. Because the humidity changes with temperature, the accuracy of measuring humidity will lose its practical significance. Therefore, we must first control the temperature control of humidity, which is a large number of applications are often temperature and humidity - body sensors instead of simply the sake of humidity sensor.

In most cases, the accuracy of ±5% RH is sufficient if there is no accurate temperature control method or if the space under test is unsealed. For those applications that require precise control of constant temperature, humidity, or humidity, or where moisture changes need to be tracked at any time, use a humidity sensor with an accuracy of ±3% RH or more. Corresponding to this temperature sensor, its temperature measurement accuracy must be more than ± 0.3 °C, at least ± 0.5 °C. Accuracy higher than ±2% RH is not even a standard humidity generator for calibration sensors, let alone the sensor itself. According to the article in the humidity chamber of the National Standards Material Research Center, “The relative humidity measurement instrument is still difficult to achieve 2% RH accuracy even at 20-25°C.”

3. Consider drift and temperature drift when almost all sensors are present. Since the humidity sensor must be in contact with atmospheric moisture, it cannot be sealed. This determines its stability and longevity is limited. Under normal circumstances, the manufacturer will mark the effective use time of 1 calibration as 1 year or 2 years, and will be responsible for recalibration. Ask the user to consider the channel to be recalibrated in the future when selecting the sensor. Do not try to be cheap or superstitious and ignore the after-sales service.