Relative humidity conversion using dew point sensor

What is dew point?

Condensation of water vaporIn other words, dew is the condensation from gas to liquid. Dew pointof Dew point temperatureIt is called (Dew Point Temperature) or dew point or dew point.

Relative Humidity changes with temperature and Absolute Humidity is always constant when the dew point temperature represents a certain relative humidity value because a certain amount of moisture is contained in the air. As the temperature of the gas gradually decreases, the relative humidity gradually increases. This is because as the temperature decreases, the amount of water molecules that can exist in the gas phase (Water Vapor) gradually decreases.

If the temperature is continuously lowered, the relative humidity becomes 100%, and moisture changes from gas to liquid, causing condensation. This is dew. This point of dew formation is called the dew point temperature or dew point or dew point.

Therefore, if there are many water molecules contained in the gas, condensation will begin to occur soon after saturating humidity even if the temperature is not lowered. That is, the dew point temperature is high.

Why is the relative humidity obtained using the dew point sensor?

Typically, percentages are used to measure relative humidity. However, when the moisture contained in the gas is very low, the% unit expressed as 0.0001% becomes very uncomfortable. PPM (Parts Per Million), mg / 1 or g / M³ are mainly used to express this value.

However, these units are also used for scientific purposes, but the conceptual difference is not very convenient in the industrial field. In addition, since moisture in the gas often affects condensation, the relative humidity is mainly expressed as dew point temperature.

Just use a relative humidity sensor, but why measure the relative humidity after measuring with a dew point sensor and a temperature sensor? To know the relative humidity in a very high humidity environment is. Thin film leather humidity sensors that are generally used have poor life and precision in environments with very high humidity. Therefore, in a high-humidity environment, it is often measured with a dew point sensor.

1. Relative humidity conversion method using dew point sensor in Radionode365

Basically, you can know the dew point by using the virtual channel of Radionode365.
Relative humidity can be determined using the dew point (dew point) and the temperature value.

UA20Tested by connecting 2 sensors (1 channel: dew point (dew point) sensor (E + E Elektronik EE1950), 2 channels: temperature sensor (E + E Elektronik EE451).

1. EE1950 PDF DataSheet Download
2. EE451 PDF DataSheet Download

Figure 1 shows the wiring connection method for receiving data values ​​of 4 20-2mA output sensors (CH1: temperature sensor, CH2: dew point sensor). If channel 1 sends the dew point sensor value and channel 2 sends the temperature sensor value, Radionode365 calculates and displays the relative humidity value.

2. Add Radionode365 Virtual Channel

If you need device settings, please click the link below to register the device first.
◎ Register a new device

1. Device Settings> Channel list Add Virtual Channel (Beta)After clicking the button, in the template selection User-defined (Direct editing)를 선택 합니다.

2. Enter the formula for calculating the relative humidity from the temperature and dew point in the script.

Copy the script below and apply it to the script to calculate the relative humidity.

return (math.exp ((17.08005[Td]) / (234.175+ [Td]))) / math.exp ((17.088005[T]) / (234.175+ [T])) * 100;

To know the humidity value from the dew point, we need to add both temperature and dew point to the variables.
T: Temperature, Td : Dew point
(The variable name should be the same as the variable name of the script, T (temperature), and Td (dew point).)

3. After saving, create dashboard and data view to record and check data.