Differential pressure transducer

LadderLogic

Member
Join Date
Jun 2003
Location
Chicagolandia
Posts
1,484
I am looking for a differential pressure transducer for a lab automation project.

We need to be able to accurately measure level of water in a glass burette. The maximum level is 250 mm and we are seeking the resolution of at least 0.5 mm. However, the measurement system is pressurized by air up to 200 psi...

I have been doing some searching, but all I could find either works in much higher pressure range or is not capable to withstand 200 psi.

Does any one know of such a thing? Thanks in advance.
 
Transmitter

Honeywell makes a unit in the ST 3000 series 100 that should work.
You can have it spanned to 0-250mm of H2O for maximum resolution. The pressure rating of the body should well exceed the 200 psi that you are looking to achieve.


Dave
 
I don't beleive Diff. Press. is the good way to make this measureent. Thinck outside the box.
 
Mtn_Bkng_Dave, thank you. I'll take a look.

Pierre, for a number of reasons, we do not want to insert anything into the burette, be that a float or an ultrasonic sensor. I also don't think an ultrasonic sensor can provide the resolution I need.

Are there any other methods I might be missing?
 
Ladder,

For more info see
http://content.honeywell.com/imc/pdf/fi/34-ST-03-60.pdf
Check with honeywell to be sure about the body pressure rating though. They dont list any info in the brochure about it but I think off the top of my head its 600psi on most of the transducers they manufacture.

As for other methods if anyone can "contribute" any I would sure love to take these DP cells with bubblers out of my caustic and acid tanks because its nasty "in that box". :D

Dave
 
Do I get this right?

Your need is to measure the level based on pressure differental caused by the volume displacement of the fluid in a seald vessel?

If my understanding is correct, why not measure the level by weight? Place the fluid vessel on a scale, or stran guage of some type.

Mike.
 
Mike,

The reason for using differential is the elevated pressure in the process.
Vertical linear measurement of water column is a primary pressure standard.
A single ended pressure transducer wont work because it will read the 200 psi plus the pressure of the water column acting on it decreasing the final resolution. Also changes in barometric pressure due to weather would also be a factor in an accurate measurement unless an absolute pressure transducer is used.

A sensing tube is installed at the bottom of the vessel and the other in the head space above the vessel. Doing it in this manner neutralizes the effect of all external and internal pressure forces and only measures the pressure of the column of water which in turn yields the correct height.

Dave
 
Dave,

As you can tell this is not my area of expertise. Thanks for clearing that up for me. Now I know something new.

Mike.
 
While researching the topic, I ran into something interesting I've never heard of before:

http://www.machinedesign.com/ASP/strArticleID/55724/strSite/MDSite/viewSelectedArticle.asp

It is my understanding this thing doesn't exist as an off-the-shelf item yet - there is only an idea, the patent and the samples. Nevertheless it looks promising - if not for my problem, then for Dave's. Who knows, maybe someday he will not have to crawl into those nasty caustic tanks anymore...
 
Looks like a neat idea but I am sure that the caustics and the +90% purity mixed acids I have to measure would turn that into as Emeril would put it..."yum yums" :D I had a hi level capacitive probe in one of the acid tanks that was only exposed to the vapor and a nitrogen blanket. Stainless steel was devoured in about 3 weeks along with the fiberglass piping from the conservation vent to the scrubber.... Nasty stuff.



Dave
 
Last edited:
Really outside the box!

OK, now if I understand the liquid(water) is visible through a glass container. If so you may have a perfect application for vision recognition software. Check out LabVIEW by National Instruments.
Here's a quote from the website.

"The National Instruments LabVIEW Vision Development Module is for scientists, engineers, and technicians who are developing LabVIEW machine vision and scientific imaging applications. It includes IMAQ Vision, a library of powerful functions for vision processing, and Vision Assistant, an interactive environment for developers who need to prototype LabVIEW applications quickly without programming, or who need off-line inspection. "

I attended a workshop for National Instruments several years ago and was wowwed by the vision recognition applications they were developing. If you have a clean environment that you can set a video camera on the process, the software can convert the picture to a value that can be used for alarming, whatever.
Way to advanced for my backward company but if you are in a lab...take a look.

for 250mm at .5mm resolution you would likely require a picture with 1000 pixel vertical resolution (.25mm/pixel) but I am no expert.

Also if the water is clear you may have to add a dye to it.

Brian.
 
Thank you, Sliver, this is really outside the box - and outside of anyone's pocket too... I wish my customers were of a "crazy zillioner" type but, unfortunately, they are not.
 
Hello,

Pierre, for a number of reasons, we do not want to insert anything into the burette, be that a float or an ultrasonic sensor.

If you were going to use a differential pressure transmitter you also have to insert something into your burette. You even have to make two insertions. An other option is a radar sensor, there more accurate then an ultrasonic and offcors also more expensive.

Why is measuring the level by a weighingscale not possible, the only thing you need to know is the temperature?

Rudi
 
Although I have called it a "burette" (that is what the customer calls it), it is not exactly the thing you would find in the science class.

This is a glass cylinder, with the level marks etched on it, mounted on the panel between two blocks of lexane-type plastic. The plastic blocks already have ports drilled into them, adding a couple more small holes would not be a problem.
 
diff pressure

If you want to use a meassure principle of dif. pres., in a closed tank under pressure, at least the preassure must be cnst.
otherwise, you can't use this principle.

What you can use (but it's more expensive) is a displacer.

That's the principle that is often used on destillation collums.
They are always under pressure (not constant the same pressure).
And the measuring pipe (burette) is placed outside. Connected by two connections (one at the upper side and one a the lower)

Greetings
Walter.
 

Similar Topics

I am updating controls on a leak tester, from a SLC 5/02 to Compact Logix. The SLC used a DDV instruction to help scale a differential pressure...
Replies
17
Views
4,272
Any recommendations for a DIY home automation suppler that has a inexpensive WiFi device that I can use to monitor my HVAC filter. Thanks, Bob O.
Replies
13
Views
3,308
On site we have Yokogawa EJA110E differential pressure transmitter connected to process air line. I'm not sure if this can be used to measure air...
Replies
9
Views
4,357
Hi, I am working on a current system using a Bailey Differential Pressure Transmitter. Unfortunately the label is torn off, the only thing left...
Replies
2
Views
1,675
Has anyone used a sensor like this on flammable gasses like natural gas? I have an orifice plate installed in a gas line that I'd like to...
Replies
17
Views
7,022
Back
Top Bottom