HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Comments
View Comments: Newest First|Oldest First|Threaded View
Page 1/2  >  >>
William K.
User Rank
Platinum
Corrosion and water entry.
William K.   3/12/2012 8:15:54 PM
NO RATINGS
I have seen thermocouples hose water 50 feet, I have seen the shield braid on RG8/U cable hose wate farteher than that. BUt thermocouples are cheap and easy and adequate for many applications, that's why folks use them. I also had a situation on a house that we purchased where water ran out of the entry panel when it rained, because the cheap person who installed the entry cable did not use an extra foot for the drip loop.

Water Proof encloseures will fill with water brought in by cable and conduit problems, so the very best choice is to have a drain in the enclosure bottom. But be sure that water can't enter by the drain opening. Another method that will prevent water entry is to have a pressurized enclosure, with sufficient air pressure to prevent water entry. This has been used on communication cables for many years. It is an expensive option, but much cheaper than fixing the problems caused by moisture entry. Of course, you must use dry air or dry nitrogen for pressurizing. That might have worked on the tug boat problem.

Walter
User Rank
Silver
Re: Water intrusion is a hard enemy for instrumentation purposes
Walter   3/12/2012 12:45:32 PM
NO RATINGS
Why do you use thermocouples?  RTDs (Resistance Temperature Detectors) are more accurate, more reliable, cost less and are more corrosion resistant.  Other than that there's no reason to use them.

Critic
User Rank
Platinum
Re: RTV
Critic   3/12/2012 12:10:41 PM
NO RATINGS
Not all RTVs outgas significantly!  This is something to consider when selecting an RTV, though.

Critic
User Rank
Platinum
Condensation
Critic   3/12/2012 12:03:29 PM
NO RATINGS
It is important, if you want to keep water out of enclosures, to consider that the water entering the enclosure may not be in liquid form.  Some seals are great for keeping out liquid water, but may not prevent humid air from entering the enclosure.  When the temperature drops, the moisture in the air condenses and ends up as liquid water inside the enclosure.  Solutions include pressurizing the enclosure with dry air or an inert gas, making the enclosure air tight (as well as liquid-tight), or adding a condensate drain if high humidity inside the enclosure can be tolerated.

Battar
User Rank
Platinum
RTV
Battar   3/12/2012 11:36:19 AM
NO RATINGS
Watch out for the RTV. It outgasses acidic fumes when curing, and that can accelerate corrosion. If you seal warm damp air in a gas tught box, the humidity will condense when you cool it at night.

bob from maine
User Rank
Platinum
Re: Water intrusion is a hard enemy for instrumentation purposes
bob from maine   3/12/2012 11:26:49 AM
NO RATINGS
Something to think about: If you make a sealed box with wires entering it and you daily heat this box to temperatures significantly above ambient, then at night cool it, you have made an efficient pump. If the box is vented, the vent needs to be in a location that draws in dry air. If it is not vented, the box will find a way to breathe expelling and replacing the air from somewhere.

bob from maine
User Rank
Platinum
Re: Capillary
bob from maine   3/12/2012 11:18:08 AM
NO RATINGS
I've had radar lines on a 90' sailboat mast dump water into a junction box that was sealed. Every fall when the mast was removed, the terminals in the box would be severely corroded and the wire needed to be stripped-back to find bare wire. The wire was sealed in the radar dome and sealed in the junciton box, however in winter the mast was stored horizontally with the dome removed and the wire exposed. Somehow water got into the cable and until it was replaced, caused corosion in the sealed box. Once you see this, you can find the same symptom in other areas. It makes for interesting trouble-shooting.

sensor pro
User Rank
Gold
Re: Can naval tech help washdown?
sensor pro   3/12/2012 10:23:33 AM
NO RATINGS
In my experience the scheduled cleaning of the service equipment was the biggest issue with corresion.I noticed that seals were not holdig with time and the quarterly cleaning let some moisture inside. This was the main cause for corrosion on power terminals and transformers, especially where the thermal cycling was evident.

Battar
User Rank
Platinum
Capillary
Battar   3/12/2012 10:16:18 AM
NO RATINGS
Capillary action can draw water between the strands inside a cable from the connector outside the watertight box. a gastight gland is no protection against this.

It's worth remembering that a 1$ plastic bottle of soda has a perfect gastight screw-top seal with no o-rings or RTV.

Aldo Agraz
User Rank
Iron
Water intrusion is a hard enemy for instrumentation purposes
Aldo Agraz   3/11/2012 10:06:00 PM
NO RATINGS
Currently I am working on the characterization and performance evaluation of solar collectors, we are using thermocouples for temperatures measurment in a closed loop of solar collectors in order to read temperature elevation of a recirculation fluid. One of our headaches is water in the terminals of the sensors, it produces oxidation in the ferrite metal of the thermocouple and therefore lecture errors, if anyone can suggest an efective way to isolate thermocouple terminals from water it will be really appreciated. 

Page 1/2  >  >>


Partner Zone
Latest Analysis
The promise of the Internet of Things (IoT) is that devices, gadgets, and appliances we use every day will be able to communicate with one another. This potential is not limited to household items or smartphones, but also things we find in our yard and garden, as evidenced by a recent challenge from the element14 design community.
Researchers have developed a new flexible fabric that integrates both movement and sensors, introducing new potential for technology-embedded clothing and soft robots.
Made by Monkeys highlights products that somehow slipped by the QC cops.
If you didn't realize that PowerPoint presentations are inherently hilarious, you have to see Don McMillan take one apart. McMillan -- aka the Technically Funny Comic -- worked for 10 years as an engineer before he switched to stand-up comedy.
The first Tacoma Narrows Bridge was a Washington State suspension bridge that opened in 1940 and spanned the Tacoma Narrows strait of Puget Sound between Tacoma and the Kitsap Peninsula. It opened to traffic on July 1, 1940, and dramatically collapsed into Puget Sound on November 7, just four months after it opened.
More:Blogs|News
Design News Webinar Series
11/19/2014 11:00 a.m. California / 2:00 p.m. New York
11/6/2014 11:00 a.m. California / 2:00 p.m. New York
10/7/2014 8:00 a.m. California / 11:00 a.m. New York
12/11/2014 8:00 a.m. California / 11:00 a.m. New York
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Dec 1 - 5, An Introduction to Embedded Software Architecture and Design
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Last Archived Class
Sponsored by Littelfuse
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service