Level Measurement for a difficult application
Level Measurement for a difficult application
(OP)
Hello everyone!
I've been racking my brain for a bit trying to figure out the best option for this problem.
I have an application with a very viscous resin and a powder catalyst being mixed in a small vessel (a very small one I will elaborate later). I would like to know the level on this vessel but there are a few problems:
1) The vessel can't be too big (I'm thinking maybe 4-5 inches of fluid maximum) because we want to minimize the residence time of catalyzed resin.
2) It would be best if the sensor is non-contact because catalyzed resin will build up on any type of contacting device
3) The catalyst is a powder and makes things very cloudy inside the vessel.
I have thought of the basics, laser (worry about particulates), ultrasonic (also worry about particulates, however maybe this isn't a big problem?), capacitance (rejected because of contact with fluid), Radar (this on seems the best but where can I find a small one?)
I guess I'm in between ultrasonic and radar but I'm not sure which is best. I'm a little worried about the dust with the ultrasonic but like the price and size (i've seen smallish ones). Is there a good small radar out there that will do better? Is this even the right direction in your opinion? Any help would be appreciated. Thanks!
I've been racking my brain for a bit trying to figure out the best option for this problem.
I have an application with a very viscous resin and a powder catalyst being mixed in a small vessel (a very small one I will elaborate later). I would like to know the level on this vessel but there are a few problems:
1) The vessel can't be too big (I'm thinking maybe 4-5 inches of fluid maximum) because we want to minimize the residence time of catalyzed resin.
2) It would be best if the sensor is non-contact because catalyzed resin will build up on any type of contacting device
3) The catalyst is a powder and makes things very cloudy inside the vessel.
I have thought of the basics, laser (worry about particulates), ultrasonic (also worry about particulates, however maybe this isn't a big problem?), capacitance (rejected because of contact with fluid), Radar (this on seems the best but where can I find a small one?)
I guess I'm in between ultrasonic and radar but I'm not sure which is best. I'm a little worried about the dust with the ultrasonic but like the price and size (i've seen smallish ones). Is there a good small radar out there that will do better? Is this even the right direction in your opinion? Any help would be appreciated. Thanks!
- Bizzy





RE: Level Measurement for a difficult application
A variant on the laser is a line line generator that's imaged by a camera. The image is processed to determine why the line image is distorted, and the result is what surface profile is. Since the laser profiles along the entire line, you can mitigate surface irregularity impact on the level measurement:
http://w
There are also 2-D laser profilometers: http://w
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
Chinese prisoner wins Nobel Peace Prize
RE: Level Measurement for a difficult application
Yes the powder floats in the air. When I said it makes things cloudy I meant that the inside of the vessel has powder floating all over the place. We have to keep the vessel covered so that powder doesn't get all over the place.
Now that I think about it, the resin becomes cloudy in appearance as well..... that may have been the source of confusion :)
- Bizzy
RE: Level Measurement for a difficult application
I wouldn't necessarily rule out capacitive sensors. Seems to me that there ought to be a way to protect the sensor head and still get it to work for your application.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
Chinese prisoner wins Nobel Peace Prize
RE: Level Measurement for a difficult application
Thanks for your suggestions so far. Any ideas who I could talk to (vendor?) that would be able to work with me through this problem? I don't have much experience with lasers.
If anyone else still has ideas I am open to hear them. I'm still trying to find a solution. Thanks!!
- Bizzy
RE: Level Measurement for a difficult application
Banner engineering has some small ultrasonic transducers that might work better for a short shot on your small vessel than the Milltronics/Siemens industrial monsters intended for long shots on silos and large tanks.
http://ww
RE: Level Measurement for a difficult application
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Level Measurement for a difficult application
Or would measuring the weight of the vessel and contents suffice?
With a weigh scale, there is no intrusion/entrance into the vessel to determine its contents. Everything is external.
______________________________________________________________________________
This is normally the space where people post something insightful.
RE: Level Measurement for a difficult application
Level is the concern for overfill. I though about weight too but this hopper would be attached to a ~300 pound mixer and there would probably be less than a pound of resin in the hopper. I worry about being able to get good data from it.
@danw2,
Thanks for the ultrasonic suggestion. I will take a look. Do I need to worry about and ultrasonic transducer with the particulates in the air? At what point do the particulates interfere with the reading? Thanks!
- Bizzy
RE: Level Measurement for a difficult application
I don't know the answer for that. Operation in dust environment with the large tank/silo instrumentation was/is purely empirical. Getting out of a fill stream was a must. other dust could be handled in some amount. Radar tends to be better at shooting through dust, but I don't know who makes a 'short shot' radar.
I suppose there's some suspended-solids-in-the-air measurement, but the vendors don't supply such a factor, probably because the material makes a difference, the distance makes a difference and most people don't have whatever instrument it is that can take the measurement, anyhow. It's more practical and easier to plop in a transducer, power it up and see whether it works.
I haven't priced them, but I suspect that those Banner units aren't beyond the price where one can be bought just to try it.
RE: Level Measurement for a difficult application
The scale might, but I am guessing there will be piping that will scew that measurement.
I would consider a Nuclear gauge. I have had to use this in similar applications in the past.
RE: Level Measurement for a difficult application
If required resolution needs to be extremely tight, a load cell will probably be the best option here. Good ones have accuracy to within 0.03% of full range.
Radar does not accurately read below 6 inches of liquid as it pierces the material and reflects back the bottom of the tank resulting in a constant zero level reading. That eliminates it entirely.
Ultrasonic that resides on the lower end of the frequency range is capable of handling dusty conditions, but finding one is difficult. In general, ultrasonic resolution isn't very accurate for such a small span, so count it out if you need high resolution.
You also mentioned this tank is mounted on a mixer. Does the level need to be measured during agitation? Yes? Then resolution of laser and ultrasonic will be highly diminished.
This brings us back to the load cell. Highly accurate and widely used in batching operations just like this one.
RE: Level Measurement for a difficult application
ht
Best,
Medeski
RE: Level Measurement for a difficult application
Endress and Hauser has been good to me in the past for an ultrasonic indicator. I've used this one before on a couple of powder dilution systems where the vessel gets pretty cloudy and it never seemed to be an issue. The only thing I would ask them about is if it would be accurate in such a short range.
http://www.ca.endress.com/#product/FMU40
RE: Level Measurement for a difficult application
Check out the first 90 seconds of the video here
ht
that shows the instantaneous response to the addition of a 500 gram weight to a 1500 Kg mixer on load cells. It is not your run-of-the-mill load cell.
claimer: this product is sold by my company.
RE: Level Measurement for a difficult application
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Level Measurement for a difficult application
If you have the time and inclination, look into Coriolis meters to measure the mass flow of catalyst and resin into your vessel. I would only use Micro Motion for this application. But, you can look into E+H, Krohne, Yokogawa, Foxboro, etc.
The dust created by the catalyst and the size of your mixing tank are going to prohibit the use of many technologies such as ultrasonic and radar. I put ultrasonic on some "non-dusty" product tanks many years ago and the dust was a huge problem. I didn't think there would be enough dust but there was. Operations was unaware of the dust created by the finished product. Radar wouldn't have worked either. I've heard recent stories of radar signals being effected by too much dust. They didn't quantify how much was "too" much. I've also heard stories of vapor effecting radar but, there again, don't have quantifiable information.
The way I understand your setup, small hopper attached to ~300# mixing tank, you'll need to have an excellent mechanical installation for any load cells to prevent measurement interference. Then again, you may be able to overcome this with experience and trending rather than precision measurement. Some processes run this way quite successfully.
Do you need to account for the angle of repose of the catalyst? Don't know your process but it may be something that needs consideration to measure the true quantity of catalyst in your vessel, with distance type instruments.
You could use a Coriolis meter on the resin and maybe an auger on the catalyst. Some paint manufacturers use augers to meter pigment into mixing tanks. I've never reviewed them and cannot comment on accuracy, size, flow rates, etc. My plant produced smaller volumes and we couldn't economically justify the equipment used in the larger plants.
You may be able to convince your suppliers to provide the quantities needed prepackaged thereby eliminating any measurement needs. Unless you want/have to buy in bulk. I would review the economics of those two situations.
Those are some thoughts that popped into my mind. Yours thoughts may vary.
RE: Level Measurement for a difficult application
Why do you want to know the level?
Overfill protection?
As I understand it, this is a batch reaction and from what you say, after each batch you presumably have to clean the vessel.
So if you start with an empty vessel and charge it with pre-measured amounts of each component, how can you overfill the vessel?
Once charged you seal the vessel and then agitate.
When you agitate you won't have a stable level anyway.
With a lid, nothing will escape during mixing.
On that basis the problem is really how to accurately charge the vessel with each component. You could then use load cells, meters or whatever.
And, presumably, once charged and before you start the agitator or fit the cover, someone can eyeball the contents?
But, if what you are trying to do is evaluate how the behaviour in the vessel during mixing/agitation, then that's something else again.
JMW
www.ViscoAnalyser.com
RE: Level Measurement for a difficult application
Close to full = thud
Empty = ring
I would think a piezo transducer/microphone bonded to the outside of the reservoir would be isolated enough to mostly pick up response of the vessel wall and not ambient noise.
Developing a control system for this may be more than you want to get yourself into, unless this type of product is already commercially available (no idea.)
RE: Level Measurement for a difficult application
Nuclear switches are sometimes considered the last resort because of the issues mentioned above. But they work very well in the toughest applications. Once they are installed, they are maintenance free. If you decide to go that route, I recommend you call Berthold Technologies.
http://www.berthold-us.com/industrial/contact.htm
RE: Level Measurement for a difficult application
@jmw
This is not a batch process. It will have to run continuously for several hours before being taken down for cleaning.
The main purpose is prevent overfill (wasted resin) or underfill (air gets mixed into the resin catalyst mixture).
Since we can't be having a bunch of resin/catalyst mixture sitting around curing we make it continuously during production. We also want this vessel to be fairly small for that reason.
I think it is possible to reduce the dust based on how we feed the catalyst (powder) into the tank. If that is the case then things get a little easier.
I am hoping for an analog measurement of some type, possibly multiple switches.
- Bizzy
RE: Level Measurement for a difficult application
Multiple level measurements, multiple floats. Disposable floats, weight gain from resin coating would not affect operation. No problem as long as the floats don't stick together.