Operating Below Dew Point

Q: What are some general tips and guidance when operating my Proteus paddlewheel type flow sensor below dew point?

A: Insulating foam and ambient controls are the most common solutions when operating a Proteus paddlewheel type flow sensor below dew or freeze point. (Proteus also offers Vortex type flow sensors, which are covered in a separate note.)

Definition of “dew point” from Wikipedia:

The dew point is the temperature to which air must be cooled to become saturated with water vapor. When further cooled, the airborne water vapor will condense to form liquid water (dew). When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface. When the temperature is below the freezing point of water, the dew point is called the frost point, as frost is formed rather than dew. The measurement of the dew point is related to humidity. A higher dew point means there will be more moisture in the air.

Generally, dewing and frosting become issues at lower temperatures. With dewing, frosting and hot/cold cycles, water dripping/pooling occurs below the flow sensor. This can create problems since it behaves like a small leak in the user’s system or process area.

Key points:

• Insulating foam covers are used on sensors to reduce condensing and freezing problems:

o On the sensor’s flow body
o On the sensor’s electronics enclosure
• Sensor’s IP or NEMA rating?
• Use of secondary enclosures to contain sensors.
• Control of ambient temperature and humidity.

Custom Foam Covers for Proteus Paddlewheel sensors:

Proteus utilizes custom designed closed cell foam covers for our flow sensors to prevent condensation and freezing of the meter when operating below dew/frost point. We have a large and growing library of foam designs for various applications. Depending on the application, foam covers may be used around the flow body, or the electronics enclosure. You are welcome to use an existing design, or we will develop one for you.

Enclosure ratings – sensors electronics and secondary enclosures:

Proteus paddlewheel flow meters used for below dew/freezing point are NEMA4X rated. They can withstand external condensation and freezing build up. Some customers prefer to use a secondary enclosure with a controlled environment (nitrogen purged or Clean Dry Air) to eliminate the need for foam or reduce the size of the foam cover.

Ambient controls:

Customers can control the surrounding ambient environment (the entire room or a secondary enclosure/box) by using air dryers/dehumidifiers as well as temperature controls which can reduce or eliminate condensing and freezing cycles

Proteus standard & custom foam services

“Customization is our way of life!”  Proteus Industries is happy to work with OEM’s to develop a standard or custom foam solution for your below dew/frost point use.