Poly beads level detection

[dr pepper]

2 1.6mm tig welding rods tie wrapped to each side of a piece of 20mm plastic ega tube conduit.
I got around 20:1 variance in capacitance.
Static might be an issue, the poly is 'sucked' out of the silo by a vacuum conveyor system, but thats only every few minutes, so could be dealt with in software, protecting the measurement system will need some consideration.

 

[dknguyen]

2 1.6mm tig welding rods tie wrapped to each side of a piece of 20mm plastic ega tube conduit.
I got around 20:1 variance in capacitance.
Static might be an issue, the poly is 'sucked' out of the silo by a vacuum conveyor system, but thats only every few minutes, so could be dealt with in software, protecting the measurement system will need some consideration.

TVS diodes? No idea what kind of static energy is built up in this kind of thing though. Will add bit of capacitance though. Probably not enough to matter. But no idea what kind of static is built up in these things

Is the tube filled or empty?

 

[dr pepper]

The earth cable has failed a couple of times, and people have been sent flying, so's theres a fair old static charge build up.
I could isolate the oscillator part of the system to lessen damage through discharge to ground.
The ega tube was empty, I probably would use it on the final design as I cant get long enough lengths.

 

[alec_t]

I cant get long enough lengths.

Couplers and solvent-weld ?
Have you considered putting the wires inside the tube, for protection?

 

[dknguyen]

Couplers and solvent-weld ?
Have you considered putting the wires inside the tube, for protection?

how do you adhere it inside a tube that long?

 

[kinarfi]

I have seen the use of strain gauges work well on tanks, one on each leg of the silo.

 

[ChrisP58]

The earth cable has failed a couple of times, and people have been sent flying, so's theres a fair old static charge build up.
I could isolate the oscillator part of the system to lessen damage through discharge to ground.
The ega tube was empty, I probably would use it on the final design as I cant get long enough lengths.

Do you need constant, real time measurements?
If occasional updates are OK, I'd suggest connecting your electrodes to the common contacts of a DPDT relay. Connect the normally closed contacts the the grounded tank wall, and your oscillator to the normally open contacts. Then just energize the relay to make a measurement.

 

[alec_t]

how do you adhere it inside a tube that long?

You don't. You use spacers at intervals along the tube.

 

[dr pepper]

Ega tube is not going to survive in the tank, refills get pretty energetic, thick wall hose would be better methinks, need to find a way to secure wires inside it.
Yes updates every few minutes is fine.

 

[ChrisP58]

Is this project still pending? Or is it all wrapped up, delivered and making everyone happy?

If the former, what wire spacing do you need?
What distance out from the tank wall?
How long does the sensor need to be?
Any special requirements for the wires?

 

[dr pepper]

Nope not finished, I have lots of other responsibilities and for the now occupied.
Wire spacing can be up to 150mm (tank hole size).
The sensor needs to be about 10 meters long.
If the wires are exposed in contact with the poly I'd use 316 stainless, if insulated no special requirements.

 

[kinarfi]

Is it possible to post a photo of the tank, if it's 10 meters tall, I would assume it's a round tank, probably standing on 4 legs which makes it a candidate for strain gauges bonded to each leg. When I worked construction at a soda ash plant, I worked on a tank which trona oar in it and just for fun, I hopped into the tank and the weight read out increased accurately, 250 pounds. I was very impressed, might be worth your time to investigate.

 

[dr pepper]

Its outside and I'm working overnight so it'll have to be next week for a pic.
The tank is round yes, however its not on legs, the circular wall goes all the way to the ground, there is a conical base welded in part way up for the outlet, that way the bottom of the silo is weather and theft/tampering protected.
There isnt a hole big enough anywhere for a person to get into the tank, probably for safety if you fell in you'd suffocate.

 

[large_ghostman]

Actually capacitance seems perfect, seeing as you get poly capacitors. Do they ground the trucks on delivery? Hows it actually done?? Like pipework for filling etc. I am asking because the more i think about it, that most be some serious energy in static when filling up. hat do they use the beads for?

 

[kinarfi]

https://www.omega.com/pptst/SGD_LINEAR1-AXIS.html
https://www.omega.com/subsection/strain-gages-accessories-all.html
here's a start for you to look at, it says you get 10 for $70.50, so several around the base in series would give you a good span, I imagine you're looking for a max reading = full & min reading = empty & middle =half full. This would be easy, if you want to know the weight of product, that's just a matter of more calibration. they have a chat line if interested.

 

[dr pepper]

The problem with strain guages on the outside is wind loading.

Yes trucks are grounded on delivery, its similar to cow feed, the beads are blown with a pump up to the top of the silo then in through the top, theres an air vent to allow air out and in.
The beads are then sucked into the plant with a decent sized vacuum pump.
Static certainly is a problem without an earth, with an earth though its fine.
The beads are melted then extruded into 2 layers of paper or board, commonly used for food packing.
The most reliable idea so far is 20 capacitance on/off sensors on a string.
Somewhere on this site theres a thread to when I made a esp8266 webpage thingy that showed all 3 silo's on a webpage with some nice graphics, that interfaced to the original hardware, now 40 years old and just about had it.

 

[kinarfi]

The problem with strain gauges on the outside is wind loading.

My guess is that you have never dealt with strain gauges, a large one is smaller than a postage stamp and bonded to the metal at a spot that has been prepared (sanded smooth) and then covered with silicone (at least, that how I did it). there may be better methods. I was hoping you ad access to the inside of the silo stand. Is there a web sit for the silo you're using?
One thing that I didn't say about the bin I got into to see it would weigh me, the 4 legs for the bin were 4 x 1/4" angle iron.

 

[large_ghostman]

So you cant use the silo as a capacitor if its grounded. I cant think of anything better than you already come up with, should be fairly accurate.

 

[kinarfi]

So you cant use the silo as a capacitor if its grounded. I cant think of anything better than you already come up with, should be fairly accurate.

Why can't you use the silo walls as one plate of the capacitor if grounded. The capacitive level I made used the wall of a gas tank as such. Then depending on where the holes are in the top of the tank, a single or multiple rod or pipe could be used for the other plate, they could be insulated if need be.

 

[dr pepper]

I dont have much experience of strain guages, but I do have experience of load cells they are common in industry, as I understand it a load cell is a strain guage with a mechanical interface.

Not sure what ghostie meant there, I'm pretty sure I can have the grounded silo as one of the capacitor plates.
Is there something you've thought of I havent ghostie?