Step 7 for Compressed Air Analysis : Setting up Dewpoint measurement and monitoring

The aim in compressed air systems is to produce dry and oil-free air that is low in particle contaminant with the most efficient effort. While oil and particles can be removed by complex filter systems, moisture must be removed by means of dryers (refrigeration, adsorption, membrane dryers etc.).

Since air has the ability to bind water vapor, water vapor is condensed into dew or frost as air is cooled down. At dew point temperature, the air is 100% saturated with water. Thus the air is capable of more water vapor at higher temperatures, denoted by the maximum humidity at which air is saturated with water.

Above shows a general view of the drying process in the compressed air system. At a flowrate of 10m³/min at 25^oC and 80% RH, the condensate generated is 184.4g, under which it goes through a refrigeration dryer with a dew point 5^oC to remove 177.6g of condensate ,and lastly an adsorption dryer with a dew point of -50^oC for a water content of 0.038g per 10m³/min of air going through the compressor. 10m³/min is an expected value for a 2" pipe at standard speeds (92.7 m/s), thus a compressor running at 8 hours per day is expected to generate 184.4g x 60min/h x 8h = 88,500g (88.5L) of water!

What would moisture in the compressed air distribution system cause:

1. Corrosion in functional elements, which can lead to leaks.
2. Ice formation in compressed air lines which causes obstruction and blockage.
3. Lubricant films in machines getting washed away, increasing the frequency of maintenance.
4. Increased probability of machine failure and production interruption.
5. Reduction of product quality, especially powdery goods (e.g. bacteria formation).
   

A dew point sensor consists of capacitive polymer sensor, in which the electrode is able to measure a different capacitance the water vapor enters the measuring medium. The porous cover electrode allows the diffusion of water into the polymer layer, while protecting the sensor from dust and oil. The polymer sensor can be easily cleaned with isopropanol, and can absorb and desorb water unlike Aluminum Oxide sensors. 

CS Instruments are always evaluating and continuously improving their sensor technology in dewpoint measurement, with the following key features in the FA Series Dewpoint Sensors:

• Sensor element is able to absorb and desorb water.
• Long term cycle life and stability >5 years.
• Handles a range of dewpoints from -80 to 20^oCtd 
• Auto-calibration with heating cycle to enable fast response time, particularly at low dew points and auto-calibration, where freezes/delays might occur.
  

When connected to a chart recorder such as DS400 and CS-Basic software, peak rises during hot chamber switching of hot generation adsorption dryers can be monitored, and abnormalities in peak amplitude and intervals between switching gives insights on machine failure and irregular chamber switching.

There is wide variety of dew point sensors to choose from CS Instruments, including mobile solutions for technicians, usage in explosive atmospheres, remote and integrated types. 

CS Instruments Dew Point measurement Solutions

	DP 500/510 •       Mobile dew point device		DP 400 mobile •       Mobile dew point device in a sturdy service case
	FA 510/515 •       Dew point sensor for residual moisture measurement in compressed air and gases		FA 500 •       Dew point sensor with integrated display.
	FA 515 EX •       Dew point sensor for residual moisture measurement in compressed air and gases in potentially explosive atmosphere		FA 550 •       Dew point sensor with sturdy die-cast aluminum housing
	DS 52 •       Plug-in dew point set		DS 400 •       Plug-in dew point set

Additional accessories such as measuring chamber is also available even for high-pressure applications up to 350 bar.