I have a process which takes one of two products, either ground raw meat or slaughtering floor runoff water, into an open top square tank. Size is about 1m wide X 1.5m long and 1.75m high. This tank is the beginning of a recovery process for various constituents of the waste streams, and it is very dirty.

We're having trouble finding a stable sensing method for level in the tank. We have tried conductive probes, but the ground meat product deforms and breaks the probes. We have tried a simple pressure transmitter (diaphragm type with capillary tube sense line to isolate the mechanical vibration from the pump) but we keep finding the diaphragm damaged from junk in the waste stream. We have rejected a simple float mechanism because the ground meat would dry up around the mechanical parts and seize the switch. And we are currently trying to convince ourselves an ultrasonic level sensor can stay clean enough in spite of the splash from the liquid product.

One idea that has been proposed, but we haven't seriously
considered it yet, is to install a bubbler tube in the tank with a periodic water purge of the line to keep it clean.

Does anyone have a similar problem that has found a solution, or have an idea we're missing that might help. This is getting expensive.

Thanks,
Michael
--
Michael R. Batchelor - Industrial Informatics, Inc.
Contribute to society: http://www.distributed.net/ogr/

 

http://www.almegcontrols.com/ may be able to provide a product that only has a say: 6" float on a rigid rod. As the float rises it activates the unit above the tank. Above the tank is a cylinder that can give you both a visual and continuous like 4-20 or 3 wire output. It is used in dirty applications. This system is used on shipyard totes so it is very rugged.

 

I ever face same trouble with yours. I must install level transmitter in salt dissolver open pit. In this pit, salt is dissolved by water. I decide to instal level transmitter with bubbler pipe type, because it is a cheapest way. Unfortunately, the salt vapor in bubler pipe often frozen and harden and make bubbler pipe clogged. To solve this problem I replace bubbler pipe with original 1/2 inch by 2 inch, then I supply a few water to purge a bubbler pipe continuosly to avoid pipe clogging. Actually, additional purge water will add differential pressure to transmitter. Therefore I do actual zero adjustment on transmitter after this transmitter calibrated in its original range. Change pipe to 2 inch also give effect a slow measurement, but I can compensate this problem by add supply pressure to bubbler pipe.
Until now, the level indication is stable and no problem related this level transmitter.

The last solution if this way fail, you must install non contact ultrasonic transmitter. In the market provided cheap ultrasonic meter from many vendors.

I hope it will useful.

Best regards from Indonesia
OsaKI

 

Air radar may be an alternative. It can be placed to avoid the splash. Ultrasonic may be possible also.

 

Perhaps something that works like this? Lowering a float to the surface and sensing the slack when contact is made should work for either solid or liquid and pulling it up out of the muck should prevent anything from hardening on it. Sometimes crude mechanisms work best in crude situations. Someone probably makes these. Perhaps Bindicator?

Regards

cww

 

Most ultrasonic heads have a .6 to 1 foot blanking distance, so you should be able to mount a ultrasonic up high enough to prevent any splash back from getting the head really gunky. Since the tank is open, a regular cleaning - (hose down) would not be a bad idea to keep things for getting to gunky anyways.

Got Consulting?

[email protected]

 

Hi,

I work in the food industry in the UK and we have also tested many different technologies including some vey elaborate radar systems. However, one thing always seems to let them down and this seems to be the environment in which they are installed.

I wonder if you have considered attacking your problem in a different way, we have found that the usual direct approach of measuring level is not necessarily the best option.

Would it be possible to support your tank on loadcells, from here your level would be determined by the weight of liquids/solids measured in the tank.
Depending on your accuracy requirement you could then introduce the necessary control for controling pumps/alarms or whatever you like.

The beauty with this system is that it can be kept well away from all the "spooge" in the tank and is relatively simple to retro fit.

Loadcells are available in many configurations and are extremely hardy even in the most harsh of environments, our company is testament to that.

If you wish to continue down your original route checkout this link. http://www.endress.com/

We have used their equipment and found them to be one of the best for non-contact measurement.

Hope this helps.

Paul Mann

 

We might have some equipment, which can do the job you ask for. We are a Danish manufacturer of level measuring equipment. We have many similar installations on slaughterhouses, where we use our ultrasonic level meters.
I copy this mail to our company MJK North America Inc. in the US who can help you with brochures etc. You can get in touch with us at our toll free number 1 877 MJK LINK.

Best regards,
MJK Denmark
Jens Kruse
[email protected]

 

Here are my thoughts.
1. How about a strain guage to weigh the tank? Try Metler Toledo.
2. I have put in ultrasonic meters that have gotten a lot of liquid buildup on them and they have worked pretty well.
3. How about putting a clamp on ultrasonic meter or magnetic flow meter on the supply line to the tank? The clamp on meters work well and are totally non contact nor non fouling. The only downside is that you need full pipe flow conditions.
4. How about a mass flow meter on the inflow pipe. Pricey.

Just my thoughts. Good luck.


I would assume that the meat slurry might not be liquid enough to assume a constant level so laser depth might not be that accurate.

 

Try Hyde Park at http://www.hpsensors.com/ultrasonic.asp They make an inexpensive IP68 food grade sensor that is ideal for your situation. The only thing that might be an issue is if there is foam on the waste water. They make sensors with built-in pump up/down logic. Really cool and a lot of value for the money. Prices range from about $100 for contact output to $600 for 4-20 analog output. Their SM900 would work for your application.

Bruce

 

A sure way would be to weigh the tank by mounting it on load cells but this is not the cheapest.

I would go for ultrasonics and suggest www.vega.com as a good place to look.

Their software is really good for setting the probes up as you get a trend of the echo curve making it easy to remove unwanted false echo's. You should be able to get reliable measurement with ultrasonics and the probe can be mounted high above the tank.

Good Luck

 

If you don't get foam an ultrasonic will work very well, if you do it may give you unrealable results. If build up is left behind from the splashing you will need to clean it, trouble is you will only find that out when it fails.

Instead of a bubbler you could try a top mounted hydrostatic sensor suspended by a cable or tube with a flush ceramic diaphragm, extremely robust, overload, shock, vibration and wear resistant.

Another alternative is an admittance probe designed to ignore build up by special electronics and PTFE coated too.
See www.vegacontrols.co.uk for idea's and applications

 

I would think Ultrasonic Level Transmitter should work well with this application.

[email protected]

 

Hi there,

You should try using WADDECO's simple Microwave Level Switch, this type of sensor is perfectly suited to your application: non-contact, non-invasive, cost effictive and highly reliable. See this link: http://www.wadeco.co.jp/sensorweb/
and check out the microwave sensors page.
Email me at [email protected] for more info.

Regards,

Mike

 

I believe noncontact ultrasonic technology is the best solution. I recommend the Pulsar ultrasonic level system Vanguard 90 (http://pulsar-us.com/docs/LowLit-Vanguard.pdf) and dB3 transducer (http://pulsar-us.com/docs/LowLit-dB-Transducers.pdf). This will provide accurate and reliable level measurement up to 3 meters and has a 3 degree beam angle for the small area needed. It also has a 5 inch blanking distance for close distance requirements.

Please call for questions 850-609-1777 or visit our website http://pulsar-us.com.

Robert

 

Air radar is another possibility to consider. Several manufacturers, Vega, ThermoElectron, Siemens can be considered. Top mounted non-contact.