Need help for solid level sensor

[neubex]

Im very much new to this electronics and know only basics.

Im working on a mini project called rice storage level detector. I have searched all over the web for solutions.

What ive found was using strain gauge. This confuses me since it changes resistance due to weight and wont detect the rice level.

Please advise. Thank you

 

[sky_123]

I'm sure there are lots of interesting ways to do that ; ) Maybe you get more marks for more unusual methods.
How about a piezo element (or microphone element) on the end of a spatula-type "thing", that is on a hinge, and can "slap" on top of the rice.
Then it is a timing issue : ) How long it takes for the piezo element to generate an electrical impulse is related to the time
it took for the spatula "thing" to swing from the high position until it slapped the top of the rice.

 

[neubex]

I'm sure there are lots of interesting ways to do that ; ) Maybe you get more marks for more unusual methods.
How about a piezo element (or microphone element) on the end of a spatula-type "thing", that is on a hinge, and can "slap" on top of the rice.
Then it is a timing issue : ) How long it takes for the piezo element to generate an electrical impulse is related to the time
it took for the spatula "thing" to swing from the high position until it slapped the top of the rice.

Thanks for the reply =)

What I have in mind is that, a sensor will detect if the rice is still at high or low level of storage.

The other sensors found in net are mostly for industries and extremely expensive. i.e. capacitive level sensor

 

[sky_123]

Yes, there must be countless ways to detect this, so you need to decide on a property. There are sensors for all purposes, so if you
find a physical phenomenon/property that you wish to measure/monitor, then you can look for an appropriate sensor that is sensitive to
that phenomenon, or a side-effect of that phenomenon. e.g. rice 'high' can be monitored indirectly by the property of weight for example.

If the container is transparent, then you could shine light through it, from the bottom, and a light sensor at the top. If the rice level is only a few grains thick, then
the light might illuminate the rice still (assuming the rice is translucent..), but more than (say) 10 grain layers thick, then the light will no longer be visible.
Pulse the light at a high frequency to make it detectable with an AC amplifier connected to your light sensor (photodiode).

 

[FvM]

Are you referring to level switch or level measurement?

For level switch, capacitive proximity or tuning fork sensor should work well.
For continuous level measurement, laser time of flight, ultrasonic/sonic time of flight, regular or wired radar are often used with grain silo level measurement.

 

[dselec]

Im very much new to this electronics and know only basics.

Im working on a mini project called rice storage level detector. I have searched all over the web for solutions.

What ive found was using strain gauge. This confuses me since it changes resistance due to weight and wont detect the rice level.

Please advise. Thank you

What is your resolution ? mm cm meter ???... also the-shape of the rice grain on top is usually a cone unless u have a Shaker for leveling.

 

[jiripolivka]

There are numerous types of sensors to detect loose material level in a container. Rice can be tricky for electrical sensors as its moisture content affects its permittivity. Light sensors may also be affected by various types of rice grain. I would recommend to try the ultrasonic sensor like Craftsman distance sensor sold for $10-20 at ACE stores. Sound wave is reflected from the surface of rice grains; with some tests you will see how accurate measure it offers. As the surface may be uneven, you can use three or more such sensors across the cross section of the container, operated one after another.
Distance is indicated in a digital form, in cm or inches; the range is 0.5 to 15 meters which could cover a common silo size. The devices are hand-held, use a 9V battery, and they look rugged to be used on construction sites.

 

[dselec]

"Craftsman distance sensor sold for $10-20 at ACE stores"
Cant locate that item on internet ? can u please help me find that ?
thanks

 

[jiripolivka]

"Craftsman distance sensor sold for $10-20 at ACE stores"
Cant locate that item on internet ? can u please help me find that ?
thanks

It looks everybody now prefers laser meters, but I do not think they will be as good with rice level like ultrasonic meters. Try EXTECH DT-100 ultrasonic distance meter, also e-bay has many such meters. I bought mine by Craftsman on sale at ACE hardware store, not online.

 

[dselec]

REAl cheep on amazon as low as 7$ if u buy 10 pcs... about shipping not so clear .

 

[Externet]

I prefer simple things.
I would use a string passing trough wheels O at the upper edge of the silo.
One end of the string with a larger weight WW resting on top of the grain inside the silo.
Another smaller weight W at the end of the string outside the silo.

A little motor that pulls the string towards the outside every hour, or as often as reading is needed, and then releases. That positions the inside weight on top of the grain to tell the level. Can be pulled from the outside manually too if you are after the cheapest way.

With markings along the silo outside wall, you tell the reverse position of the weight inside the silo.

Let me try a drawing:

O--------------------------------------------------------------WW<--- on top of rice
|
|
Silo wall=================================================|Floor
O-------------------W <---hanging outside

Turn the above sketch 90 degrees clockwise. "O" are wheels, "-------" is the string

 

[dselec]

I used 2 long metal plated electrodes to check water level using as capacitor and making a oscillator... sure it will work for solids as well.
first decide what is your resolution.

 

[jiripolivka]

I also like simple things! But any mechanical system like the above requires often a daily checking by a trained person.
Using the two electrodes to measure water level can work but rice is quite different a medium. Measuring water level depends on conductivity, and this varies with salt content. Corrosion on electrodes renders the system unusable after a short time. With rice and other grains the problem is that its moisture content varies, so will the detector output.

I have seen and tested many sensors for many cases; for rice I support the ultrasonic detector as it is reliable, low-cost and needs no maintenance for a long time.
For water the pressure detector looks best to me, no corrosion and no salt content problem.

If the rice container is a cylinder like a silo, I would try to design an acoustical resonance detector. Install a water-proof speaker on its axis, use a sweep-frequency audio oscillator and use speaker voltage output to detect volume resonance. The frequency of this resonance will be controlled by rice (and anything) level in it. Depending on silo volume, the frequency can be as low as units of Hertz, so you can listen or feel the resonance from vibrating wall (s).

Good luck!

 

[FvM]

The two wires can work in different ways:
- as a capacitive level switch
- as a continuous capacitive level sensor, accuracy will possibly likely suffer from moisture effect
- as a conducted microwave radar, see

Liquid level sensors are mostly using conductive detection, but capacitive is basically possible too

 

[jiripolivka]

Yes I know about all that stuff. There is a long string of International Workshops on Interaction of Electromagnetic Waves with water and moist substances, since ~1995 where you can see the gradual sensor and method development for many cases, also for rice and grain measurements. Many nice attempts turned to be "end of way" in real applications.

 

[FvM]

Many nice attempts turned to be "end of way" in real applications.

I was referring to a subset of thinkable techniques that has proved reliable in industrial applications. Acoustic TOF is among them, but it's obvious that laser TOF and radar are slowly superseding it in applications demanding some accuracy. The classical ultrasonic and sonic echo methods will stay for some applications nevertheless. A sonic echo system has e.g. the advantage of averaging a conical solid surface in a silo, I remember commercial sensors for this application.

A main disadvantage of all acoustical sensors is temperature dependent sound velocity, sensitivity to movement of air, and in some cases really worse, dependency on the gas mixture.

Unfortunately the original poster never mentioned the intended measurement accuracy.

 

[dselec]

If its a 30-50 meter height silo will ultra... work ?

 

[FvM]

If its a 30-50 meter height silo will ultra... work ?

Good point. Ultrasonic sound attenuation in air is already considerable at 50 m, in combination with diffuse reflection echo intensity will be low. That's why sonic echo sensors (e.g. 5 - 10 kHz) are used for this application. A "Resonance" measurement as discussed by jiripolivka or acoustic FMCW should work too.

 

[dselec]

So the cheapest way is to use a wheel with weight inserted and measure the marks on the cable ... a;ll done with hand and with a counter weight it will measure automatic the usage of rice.
I use that for checking height at my house.

 

[FvM]

That's in fact a very rugged measurement. Externet mentioned an automated variant, using a motor. Similar methods are used in industry e.g. for tanks with layered liquids, or liquids covered with foam.