Level Sensing!!!

[Orn Jonsson]

Hi fellars,

I have a 12Ft tall cone shaped Mixer/hopper, i.e. it is a cone shaped hopper with two rorary augers inside. I need to provide level indication for the operator.

Ultrasonic level senor seems to be the way to go, but the medium in the hopper is a very fine powedery activated carbon.

How could I prevent a false level reading, generated by the dust inside the hopper?

Are you guys aware of any noncontact level detection instruments with discriminatory settings, (build-up and dust filtering)?

Thanks,

Later,
Orn Jonsson

 

[rsdoran]

You are working with carbon black powder..fine? That stuff can be messy, gets on everything. Few years back had to work with coarse that ran thru a small hammermill then was fed into product. On our silos for gypsum and hoppers we used an ultrasonic system but the name eludes me right now, will try to locate the company name. I know we didnt have problems with dust but did have a problem with the settings because of the blowers...ie the silos breathed (or got walked on) and it would move the sensor which in turn changed the values we got.

Found it, we used Milltronics (didnt realize it was part of the Siemens group). Guess the company was an integrator.

Anyway you can find info on Milltronics at:http://www.airanger.com/

 

[alanc5]

We had a simular problem measuring saw dust. Endress hauser makes an ultrasonic probe that has material density dettings( to help eliminate dust pick-up).http://endress.com
hope this helps.

 

[Terry Woods]

Have you considered using something as archaic as a Bindicator?
You can stick them in just about anywhere. The only problem is you have to use several if you want to get any kind of resolution.

A Bindicator is a simple little motor turning a paddle. As long as the paddle is free to turn, a contact is maintained providing an "I doan see nuttin yet!" signal. When the material prevents the paddle from turning, a slip-clutch gives way and the switch changes from one contact to the other and sends an "I see whole lots of stuff now!" signal (that's assuming you use both sides of the contact).

Bin Level indicators are a real pain in the A$$. Material problems, steam, condensation, phase of the moon... just about anything can keep them from giving you a true reading. And, of course, there is that everlasting problem associated with dry containers of any kind - kling. Dry containers simply do not level out on their own so as to present a fair indication of the true level.

We have several dry bins that are subject to the conditions I described above. They give lots of problems in Spring and Fall. I've considered using some sort of scattering radar system (yeah, right).

Seems to me that that would be a pretty good project for you inventor-type dudes out there! Two sensors of some kind that provide enough info to develop an electronic 3-D picture that can be analyzed by some software to show, not only the amount contained, but also, what part of that is actually accessible - that is, not klinging to the side!


Bindicators ain't so fancy, but they're pretty damned reliable!

 

[PhilRey]

Check out Magnetrol's vibrating rod level switch at
http://www.magnetrol.com/html/solitel.asp
http://www.magnetrol.com/html/vibrate.asp
http://www.magnetrol.com/html/appsolitel.asp

 

[rsdoran]

yeah, kling and/or bridging. The silo/hopper is still half full (or half empty)and the devices can say empty or full depending how it klings/bridges. We used a lot of different type of vibrators to try to eliminate those issues.

You had to bring up Bindicators, now I will have nightmares tonite.

 

[Alan Case]

If it is a real problem and you must have an accurate reading then moount the bin on some load cells and display the weight. Its more expensive but if its the only way. Regards Alan

 

[Pierre]

IMHO - Nuke it!

 

[Dave Williams]

Along Alan's suggestion, you could use load cells. We use cells that are simply a 4-20 transducer that can be configured for pressure, weight, etc. The advantage is they are mounted in the bottom of the hopper or tank. The ones we use are made by SP-50 I believe. You simply weld the connecting flange to the bottom of the hopper & attach the device to the flange. They're not cheap, about $2000, but are very accurate. The only problem I could see in your application is if the carbon were to become compressed in the hopper, in that case you would get a false reading.

 

[Orn Jonsson]

Level Detection Instruments

Thanks for your responses guys.

I should have been a bit more descriptive on the nature of this silo/mixer.

It's a cone with an attached in-feed conveyor on the top and another attached out-feed auger on the bottom (difficult app, for load cells).
Binmaster or Bindicator point level lindicators would have been my choice if the darn thing didn't have two rotary augers mounted inside, running from top to bottom along the walls attached to a rotating "drive axle" on the top.

This leaves me with no point of penetration on the walls and a rotary drive mechanism across the top inside that will break my ultrasonic beam about four to six times a minute.

I still think the Ultrasonic Method might work if I can filter out the signal when the auger-drive-axle breaks the beeam.

Vibrating probe, Binmaster or any intrusive instrument is going to be a problem.....

Both "Endress Hauser" and "Milltronics" seem to have quite sophisticated sensors that will compensate for dust and such around the medium.

this one is going to interesting.........

Thanks again,

Orn Jonsson

 

[Mike]

Orn,

Check with your scale vendor I have in the past also worked with carbon powder and had many of the same problems you are experiencing. I found that many of the scale companies have transducers which you can either drill and tap in to the steel frame just like a bolt or a pad which is epoxied on to the frame. These transducers measure the defection of the steel to determine the load. These units are actualy very accurate, which was quite a surprise to me. It was in 1990 when I used these and I am sure that there is newer products which are more accurate than the ones I used. I belive Weigh Tronics was the brand which I used back then.

The neat thing about these is that you do not have to do any mechanical work other than drill and tap a 1/2" hole in the frame and screw in the transducers. I hope this helps.

 

[suwichai]

Hi fellars,

I have a 12Ft tall cone shaped Mixer/hopper, i.e. it is a cone shaped hopper with two rorary augers inside. I need to provide level indication for the operator.

Ultrasonic level senor seems to be the way to go, but the medium in the hopper is a very fine powedery activated carbon.

How could I prevent a false level reading, generated by the dust inside the hopper?

Are you guys aware of any noncontact level detection instruments with discriminatory settings, (build-up and dust filtering)?

Thanks,

Later,
Orn Jonsson

 

[suwichai]

Dear All,

 

[suwichai]

Dear All,
It 's may be too late for this information. Now, Endress&Hauser has the new instruments that is specially design for this kind of application. It's called Levelflex-Model: FMP40. This the Guidwire-Radar type sensor. It is very reliable for a powder,or bulk solid application

 

[JesperMP]

Two problems that I have experienced with ultrasonic level sensing (and it was milltronics !):
1: Reflexes from the bottom or other objects in the vessel can cause false readings.
2. If the vessel is 100% filled up, the sensor doesnt recieve the impulse within its "time window" (not enough distance from the sensor to the material in the vessel) and interprets it as 0% (!). Wont happen if properly installed.

I have used load cells with good results.
If you can hange the whole thing from one point, you will only need one load cell. One load cell + transmitter is approx 700 $/€.