Ideas For Level Sensor

[Brad93]

Have a small project for one of my customers.

Imagine a cylindrical tank about 2 foot deep with a conical bottom, heated to 70 degree celsius, full of gloopy plumbers flux. Incredibly corrosive to certain plastics.

They used to use a float which pushed up a rod, which moved a lever connected to a mercury tilt switch. This was operated at 230v and capable of carrying a considerable current for it small size.
It was all housed in a rather pants plastic housing with springs. Anyways the plastic broke down over time, springs shot off into oblivion. I managed to fit the tilt switch into a small metal enclosure however on first use it somehow arced out against the housing despite being in shrink tubing.

I'm now looking for a suitable alternative for fill control.

I tried a microswitch, unfortunately the force required to activate it was too much and the float doesn't have enough buoyancy to push the switch down before the flux solidifies over the top of the float rendering it useless. When it was working the pump was also coming on for 2 seconds, off for 2 seconds, etc etc which isnt going to do the pump any good.

Ideally we want the fluid level to go down 200mm then the pump runs till max, then drops 200mm again etc.

This leaves me with two options, only one of which I'm certain will work although it will require some relay logic i think to get it to do what I want.

Ultrasonic sensor, ideal as its non contact and should work acceptably off of the gloopy liquid flux.

or one of these. my only concern is the float getting bunged up with solidifying flux and then it not working. https://uk.rs-online.com/web/p/float-switches/4928946?gb=s

Anyone got any ideas? I can post some pictures today.

Can not have any plastic. Three phase plugs, cable ties, plastic cable glands - they all disintegrate and become brittle in the presence of this stuff!

 

[ajlelectronics]

Those floats are a tenner on Ebay and I have no doubt that they are one and the same.

How about a magnet on the rod and a glass reed switch for sensing?

 

[RichardM]

Used to use ultrasonic in the liquid silos at work. Worked well, better than the load gauges they installed later.

 

[Brad93]

Those floats are a tenner on Ebay and I have no doubt that they are one and the same.

How about a magnet on the rod and a glass reed switch for sensing?

That ones on eBay don't work the same

 

[Misterg]

This leaves me with two options

Have you thought about air pressure based switches?

This sort of thing, but in metal:

PLS 1 Pneumatic Level Switch

AWE LTD

www.awe-ltd.co.uk

If the product will stand some bubbles, you could add a bubbler tube fed with low pressure compressed air / nitrogen and monitor the back pressure to determine the level (just a pressure switch). Bubbler tube and plumbing could be metal & switches mounted remotely. Keep the air flowing, and no flux will go up the tube.

 

[bricol]

In water and similar solutions, we used a float with a rod vertical from it - the float or rod, I can't remember which, loosely constrained in a length of suitable hollow section.

Through the side of the hollow section, targeting the rod, we had three proxy switches for low level- stop all, fill, and stop fill/full. Needed a plc to take the signal and control pumps, valve etc. But as all non-contact, it was pretty reliable, only failing if lots of foam, when the float would sink lower than ideal.

 

[Dozzer]

in this app, Im with @RichardM ultrasonic sensor, use a relay if it need to switch larger current.
other than that, use a float make from glass or hastelloy, neither will rot but will cost and need to be made. not off the shelf.

 

[MetalMonkey]

You can get non contact capacity sensors - but I don't think that will work if it is a metalic container, which it sounds like.
https://cpc.farnell.com/dfrobot/sen0368/non-contact-capacitive-liquid-sensor/dp/SC21079

A lot of level sensing stuff is going to work off 4-20ma controls - so you might be looking at a PLC to do the control logic - might actually be easier than relays in some ways.
Really you are going to want two methods of detecting the level - primary and a backup, configured in such a way as if the backup sensor is engaged it limits the level and also raises an alarm.
i.e. you have an operating level range, and a “s**ts about to overflow” limit. Especially if its nasty stuff.

 

[Bravheart]

Proximity sensors had them in a grain silo one for off one for on. OK not such a harsh environment but there's a fair choice here. Probably ultrasonic but give them a shout can't be a million miles away.

Sensors - ifm

Display Sensors and choose from 4548 ifm products ✓ Fast delivery ✓ 5-year warranty ✓ 50 years’ experience ✓ 165,000 satisfied customers

www.ifm.com

 

[daleyd]

We use loads of non contact sensors for level detection, there’s loads of choice - radar, inductive, laser etc

As said above you’ll need something to read off the level, if you only want indication then a cheap indicator display will do, just needs to accept the input type the sensor is giving out, 0 or 4 to 20mA or 0-10 volts commonly. If you want it to actually do something when a level reaches a position (eg operate a relay, flash a light etc) then a small controller will do. You could add a plc if your feeling fancy.

 

[Hitch]

Probably 90% of sensors we fit are IFM nowadys. Lots and lots of solutions for harsh environments, contact and non contact...some will need some electronic wizardry to read/switch.

Combined with a pressure sensor, or a secondary level switch you could get a reading of how much below the fill level it is, operating the pump through a vfd could fill it steadily too.

Probably getting a bit out of control then, more control than the job is worth.


The other other brand we sometimes use if Endress and Hauser, again, some ugrade to the wiring would be necessary no doubt for that, but I'm no expert on the electrical side of automation.

We tend to fit them to setups with dozens and dozens of sensors and pneumatic valves and various pumps all controlled though plcs and a HMI screens, in control cabinets big enough to enter Narnia.

 

[GRW]

Ultrasonic gauges are what we used to use for large diesel fuel tanks. Programmable with tank dimensions to provide your levels, also can give alarms and outputs etc.

Might be worth looking on www.centretank.com
Or call and speak to Centre Tank Services in person on 0121 351 4445.

 

[Cuthy246]

Is the flux conductive?,

A couple stainless rods of appropriate lengths would be able to give an I'm too low fill me and a stop I'm full signal based on change in continuity between them, couple relays and away you go. Nice and simple not much to go wrong inside the tank.

Something like this?

 

[winchman]

Best way is to put the tank on load cells and weigh the contents or a cheaper way is a stainless float pushing a rod up a tube with a magnet on the end on the outside of the tube have a pointer or switch to sense the magnet

 

[Robotstar5]

Another vote for ifm, they have sensor solution for most jobs - example

 

[Robotstar5]

Another company to look at is Vega we used a lot of their fluid level sensors in the paint shop at JLR.

 

[winchman]

Another company to look at is Vega we used a lot of their fluid level sensors in the paint shop at JLR.

Good company also Endress and Hauser but neither will be cheap, but should give years of trouble free level monitoring

 

[Blue Chips]

I don't know how accurate the sensing needs to be within your target range of liquid levels, but a tethered sump-pump type switch can't get clogged up with any of the glop in the tank, as the switch is enclosed in a rubber/plastic bulb, and there is no external mechanism...just the rubber cord that is fixed to some location on the tank wall...and there's nothing to corrode.

https://www.kdpumps.co.uk/sump-pump-float-switch/

https://m.media-amazon.com/images/I/71Bk5Ivm2gL._AC_SX679_.jpg

 

[Seadog]

The flux eats plastic, and probably rubber.

 

[Gareth J]

Cotswold all stainless steel float switch - Mill Dairy Service

Cotswold all stainless steel float switch - complete.

www.milldairyservice.co.uk

Keeping it simple?

Pump overrun can be sorted with a simple external overrun timer.