Measuring Silo Level with Perilite Material

[anthr_plcnewbie]

I am looking for a way to determine level in a silo. The material is called Perilite which has a very light density. Bulk density could be anywhere between 2-25 lb/cub.ft. Due to this, instrumentation reps are unsure if radar, guided wave radar, ultrasonic would work at all. The height of the silo is about 90ft.
Any other ideas or technologies that could work?

 

[Toine]

Is the density fluctuating all of the time? Or can it be assumed to be somewhat constant for a limited amount of time? E.g. for one batch if this is a batch type process. If it can be assumed to be fairly constant and known for at least a limited amount of time then the silo might be put on load cells. The weight reported by the load cells combined with the density and known volume of the silo are enough to calculate a level.

 

[anthr_plcnewbie]

Thanks for the reply. These are existing silos. We are building a new roof for them hence we are looking to add something at the top. Unfortunately, cannot go the load cell route.

 

[OkiePC]

I've not used these, but have seen them recommended for many similar applications:

https://www.binmaster.com/

 

[Toine]

Do you require a somewhat exact level, or would be one low level and one high level indication be enough?

For a somewhat exact level where load cells are ruled out, it seems to me either acoustic or radar would be the way to go.

If all you require is a low level ("start refill if level drops below L") and high level ("stop refill when level rises beyond H") then two relatively affordable digital indicators would be enough. Membrane pressure switch type, tuning fork, rotating vane and the like.

 

[TWS]

These should work
https://www.bindicator.com/p/continuous-level-measurement/yo-yo-series-level-indicator/. Old technology but very reliable.

 

[saultgeorge]

Hi, I'm not sure if you would want a constant level status (e.g. 0 - 100%) or as stated simply a low and high.
I've worked on some grain silos, and some folks used a product called a "Bindicator" which was merely a diaphragm located on the side of the silo. One cut a 4" hole in the silo and mounted the device. This was on corrugated metal silos, not concrete or anything very thick. The pressure from the height of the product pushed on the diaphragm and activated a switch. Also on top there was a bindicator that used a fractional horse motor with a torque switch. The motor had a gear reduction which turned a variable length rod that had paddles attached to the bottom of the rod. The rod hung down into the silo and turned slowly (fraction of an RPM) and if the product got to the paddles and caused resistance for the motor to turn, the torque switch made and set off an alarm, or an input to stop the filling process, etc. It was not a very large device, but you would probably need AC up there. So the diaphragm switch for low level and the other for high level. Hope this helps.

Ooops!! TWS beat me to it, I guess.

 

[goghie]

When you say Perilite you mean the one used for example in Starch suspension filtration?

 

[danw]

Assuming the material is Perlite, I would be very wary about using top-mounted non-contact radar because the operating principle of level radar is the change in dielectric that the radar beam sees.

It might work when the density is high but will certainly fail with a Loss of Echo (LOE) when the density is low and there is lots of air mixed in and surrounding the medium.

Level radars have a spec of a minimum dielectric needed to as a threshold that the device can detect, for instance a minimum dielectric value of 1.3. Air has a dielectric value of 1.

The radar beam shoots through air with dielectric of 1 and has to bounce from a minimum change in dielectric. But the material is surrounded by LOTS of air so it never creates much of an echo.

I'd want to try it for an extended period to check the performance under different conditions, before making a decision.

 

[anthr_plcnewbie]

Thank you everyone.
To answer one question - Yes operations prefer to have continuous instead of two level for a high and low.
I agree with danw that the radar not being an effective way to know things as the bulk density might be too low for the material.
I have installed radar and ultrasonic type level measurement instruments in other silos with minimal issues but the material bulk density was over 25lb/cub.ft. The yo-yo type bindicator does sound like an interesting option, but have never used one so not sure on how reliable of a method it would be.

 

[TWS]

The yo-yo style level transmitters have been in use for over 50 years.
Contact the factory for support for your application. they will be able to pick out the correct weight for your application.