Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Liquid level sensors for LN2 in a dewar?

Liquid level sensors for LN2 in a dewar?

Liquid level sensors for LN2 in a dewar?


I recently joined a research group that is using a dewar for containing samples that need to be immersed in liquid nitrogen.  An automated mechanical gripper occasionally takes samples into and out of the dewar. The dewar is automatically refilled by a system that pipes in liquid nitrogen. A capacitive level sensor triggers a solenoid valve in the LN2 supply line, to maintain a sufficient level of LN2 in the dewar.

I am told that we are having problems with the level sensors because they get iced up and give a false zero reading, which causes the dewar to overflow. Obviously, we must do our best to keep the moist room temperature air out of the dewar, but some will inevitably accumulate.

My question is, what sensors exist for determing the level of liquid nitrogen in an open container?  

If anyone can give practical reference info for cryogenic techniques, I would appreciate that. I see that last year, 'eigenstate' posted a couple of books,  "Cryogenic Engineering" by Hands (1986) or "Matter and Methods at Low Temperatures" by Pobell (1991).  Do these books cover practical tachniques of LN2 system design?

Thanks in advance,
Jon Spear

Jon Spear
Berkeley Lab

RE: Liquid level sensors for LN2 in a dewar?

I have no idea what the capacitance of ice is but if it is even close to water, it should register overfull, not empty.  Maybe there is another problem.  Either way, if you don't need to know the actual level at all times and just when it is full or empty, I would switch to a temperature sensing device (2 RTD's would be my choice).  You can buy RTD switches from OMEGA or ???.  I'm not sure whose dewar you are using, but CHART and Taylor Wharton probably have a liquid level switch they offer for the dewars you're using.  They would probably be RTD's (or Differential Pressure if it's a big dewar).  You probably have to call to find out about them, I doubt they are listed on their websites.

Good luck,

RE: Liquid level sensors for LN2 in a dewar?

You might also consider using a weight scale and simply weighing how much LIN is in your dewar.

RE: Liquid level sensors for LN2 in a dewar?

Weight scale is a great idea, if not try an all stainless float switch, not sure this would work due to LN2's lower density.  Solenoids leak all the time, the Parker Gold Seal valve is petty good.  I once bought five Asco's and they all leaked.  Good Luck


RE: Liquid level sensors for LN2 in a dewar?

Try using a pressure difference level sensor which is designed for open systems however is also suitable for closed containers.

DeMaCo Holland manufacture this equipment you can visit their website www.demaco.nl

RE: Liquid level sensors for LN2 in a dewar?

I used a cork float with a wooden rod as a primitive level gauge many years ago when LN2 first showed up on the industrial scene.  Today you would probably have to use one of the foams instead of cork.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close