Products>> Test System Components>> Tools & Accessories>> BT-810 Back-to-Basics Dew Point Measurement

How does the accuracy of your humidification system affect the results of your tests?

Your test system's ability to control Relative Humidity (RH) will have a significant impact on the results of your tests.

To illustrate the effects of RH on membrane performance, consider the following:

The conductivity of Nafion at 80% RH is a factor of two less than its conductivity at 100% RH. If your measured RH is 80% when actual system RH is 100%, your results would be off by a factor of two.

For a given set point, many humidifiers produce dew points which are a function of flow rate and/or time on test. When flow rates change, as current is increasing, you may see features in the data that appear to be a function of current density. These changes may actually be caused by changes in dew points that are occurring at the varying flow rates. Changing dew points may also be occurring in samples tested over periods of time, as many humidifiers are unable to achieve stable dew point control.

Test your humidification system to verify that your system's set dew point is the same as the actual dew point.

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BT-810 Back-to-Basics Dew Point Measurement

Water Collection System

The accuracy of your test results is significantly effected by the accuracy and reliability of your humidification system. So, how do you determine the accuracy of your humidification system at the operating conditions used for fuel cell testing?

We have researched many relative humidity measurement methods and have tested several of these methods. The result is that often times the method is too limited in its operating parameters, too unreliable when compared test-to-test or too expensive. We developed the Back-to-Basics Dew Point Measurement method to address these limitations.

Theory of Operation

This unit condenses the water from your gas stream using a simple ice bath. The water is collected into a burette. The operator manually records the volume of water collected as a function of time. Given the inlet gas flow rate, the absolute pressure of the gases, and the rate of water accumulation, the dew point and relative humidity are calculated.

An Excel-based calculator is included with this unit. The operator enters the gas flow rate and the water accumulation data collected over time. The average dew point of your flowing gas is calculated from this information.

Operating Parameters

Items included with the Dew Point Measurement Unit


The following image is taken from the Excel-based calculator.


Spread Sheet Calculation