I have Endress and Hauser FMU90 transmitter and E&H FDU93 sensors. I have a silo with a conical bottom. The system seems to sense great until the material is low into the cone. Today I tried to create a linearization table and extend the range to allow the unit to pick op the waves that are obviously bouncing around after it bounces off of the angled sidewall. I have had trouble finding the right length, or combination of lengths. I saw some changes but the overall reading was unstable.

I know its a matter of setting it up to read the right echo once it ends up bouncing around.
The silo is 30' to the top of the cone, and 35 to the bottom of the cone.
I set up the 1st table like this:
1 0-0 (67.79')
2 48-0.1 (32.57')
3 100-100 (2')
This is the triangle config of the sensor waves.

Can anyone help with their insight and experience?

 

>Can anyone help with their insight and experience?

Good Luck. If you find the magic solution, please let us all know.

My experience in ultrasonic level sensing is that it does real well until the beam gets to where the side walls are no longer vertical. Than it's a crap shoot.

I've considered guided wave radar (radar that runs down a cable) for the one tank where it might make a difference, but haven't gotten there yet.

Carl

 

If you have a scope and can connect it to see the echo you may be able to point the transducer so that you get less echo off the side wall. It's also possible the gain is too high at that distance, does it have a setting like Time Variable Gain?

 

Here's how an ultrasonic transducer works. It is like a drum and an ear. You bang the drum and then listen for the echo. Bang the drum again, and listen. Repeat. The length of time it takes for the sound to originate and be received back divided by two is the distance between the sensor and the target. When you have a conical or curved bottom, you can reflect the signal off the side walls, and cause multiple ghost echos. If you have multiple echos, your transmitter has to be capable of discriminating between the real echo and the repeat echos, or the false echos. In most instruments this is impossible.

Basically, you can't use an ultrasonic level meter in a conical or curved bottom tank. You can't use a time-of-flight (pulse) open air radar gauge either. Same problem.

You can use a laser level gauge, or a guided wave gauge, or an RF Admittance gauge. In some cases you may be able to use an FMCW open air radar gauge, but that's dicey. The higher the dielectric constant of the material, the more likely you can use one.

Have you considered using a bolt on load cell?

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Is it absolutely necessary to in include non linear portion of the silo. I have used E& H ultrasonic level in many silos but never scanned the cone.
Using guided radar is only one solution that will help you in this regard.

 

Try aiming the ultrasonic sensor directly at the discharge opening of your silo. This should optimize the valid returned echo amplitude (depending upon the actual sensor mounting location) and it will eliminate the "three cushion pool shot" effect when your material levels fall into the cone. This is usually best accomplished when the silo is empty (or very nearly so). I've done this successfully for close to 100 sensors when we used to sell them.

 

Thanks all. I am not there yet. I have reverted back to my basic setup with basic silo dimensions for now. Its reads ok, but i get a sharkfin in my level trends every 13 minutes. I may look for an interference issue.

E&H has suggested giving it a greater lenth to empty value. They are convinced that I can read the cone. (or most of it, the beam hits the side of the cone) They said its a matter of tricking it to looking at right echo. Once it hits the side of the cone, it would be getting a few back.
E&H said that once I find the right lenth to get the strongest echo back is when I have the right one tuned in.

At that point its a matter of breaking it down in the linearisation table to get the ratio of fill properly reported.

 

Is the controller in MANUAL or AUTO?

A "shark fin" pattern while in AUTO can be an indication of a sticky control valve.

For more on stiction, see:
http://www.expertune.com/r2.asp?f=AList&l=articles/isa2001/StictionMR.htm

-George