露点と|その計測方法について

Hello Tony
Thanks for contacting us and showing your interest in dew point measurements. The capacitance signal is measured by converting it first to frequency, where the sensor is a variable capacitance component in the oscillator circuit. This frequency is then counted and converted to relative humidity based on the sensor calibration and linearization (this part is based on the sensor model and other proprietary algorithms that are not public, unfortunately). Please note we always measure relative humidity, and therefore, we need also precise temperature reading that is measured on the humidity sensor surface. This is a normal resistive (pt100) measurement.

With a help of this document, you can derive the dew point calculation based on the measured RH and T: https://www.vaisala.com/system/files/documents/Humidity-conversion-formulas-Technical-eBook-B210973EN-L.pdf
I hope you will also find answers to other humidity-related calculations like absolute humidity, pressure-dependency, and other humidity formulas under the same document.

Best regards
Juhani

Dear Sunny, More information on RH and calculations you will find here:
https://www.vaisala.com/en/lp/make-your-job-easier-humidity-conversion-formulas, or then you
can register for our webinar: https://www.vaisala.com/en/events/webinars/lp/real-life-use-cases-humidity-calculations
I hope the Humidity Conversion Formulas eBook and our humidity calculator tool will be helpful! Both are free.

Dear Yashwanth Kumar, Thank you for your question. Would you watch our webinar https://www.vaisala.com/en/events/webinars/lp/humidity-measurements-under-pressure to get more information on what pressure is and how it is related to humidity?

Dear Vikul, We have an excellent eGuide that helps in choosing the right instrument for your needs:
https://www.vaisala.com/en/lp/download-vaisala-compressed-air-eguide

Dear Ashok Pujari,
To find out the dew point in a certain temperature, pressure, and humidity can be solved relatively easy by using e.g. the Vaisala Humidity Calculator: https://www.vaisala.com/en/measurement/humidity-dew-point-and-moisture. With this free tool we can calculate how much the dew point maximum and minimum are. The maximum dew point happens under higher pressure, higher relative humidity and higher temperature. If we put 7 bar, 80 % RH, and 50 degrees Celsius to the Humidity calculator, we can see the calculated dew point temperature is about 45 degrees C. So, if the gas is cooled down to 45 degrees C, the condensation happens. On the other hand, if our conditions are 6 bar pressure, 60 % RH and 25 degrees C, the dew point temperature would be then about 17 degrees C. Based on this information, the dew point temperature is between 17… 45 degrees Celsius depending on the conditions.

Dear Velan, Thank you for your questions.
A) If the real frost point (dew point below zero degrees Celsius) is lower (drier) than e.g. the DMP74B, the instrument typically shows the lowest possible reading (with this product the frost point reading goes somewhere to -74 degrees Celsius because the sensor cannot anymore detect the drier condition.

B) Argon and nitrogen are both inert gases and can be measured with Vaisala capacitive thin-film sensor technology. Please note that the pressure of the measured gas has an influence on the dew/frost point and should be inputted to the MI70 handheld to compensate for the pressure effect (the DMP74B cannot measure the gas pressure itself but you need to tell it to the instrument if the pressure is not ambient, i.e. 1 bar(absolute)).

Hello Munawer. Thank you for sending your question. It depends on the moisture analyzer if it can output the dew point temperature or not. Most of the Vaisala humidity instruments can also output dew point. We are happy to advise you with all Vaisala related product questions.