water sensing electronically

Hi all,

I am working on an electronic water sensing mechanism.

In an underground water tank I need to sense various levels of water as the water level is consumed and refilled. Later I want to control the sump motor with logic when various conditions are met.

focusing on just electronic sensing mechanism there are many choices available

- biase a transistor with the help of water as conductor
- use Logic gates inputs to become HIGH/LOW when water touches probes.
several choices for gates, any gate can be used in general, even a NOT gate can do.
- Ultrasonic depth sensing.
- LDR based
- various other.

I am working with logic gates at teh moment but will transfer it to microcontroller later when I am satisfied with 'water sensing'
the problem with many techniques above are, their reliability changes with many environmental effects. water vapours, hydration, corrosion, electrolysis, temperature and many similar factors change parameters which can affect changes in sensing.

currently I am working with NAND CD4093. it has built in schmitt trigger so it can shape inputs.
I am prefereing to give oscillated inputs to this logic gate, so at least electrolysis can be prevented. probes will be usually dipped in water.

To perform oscillation in sensing probe I can use transistors ( ac biased), 555, opamp.

Q.1 which one would be better option for oscillating in this scenario?

Q.2 How can I simulate the properties of tap water in reservoir e.g. water conductance and other electrical properties in NI multisim?
currently I GND the inputs with a switch to give the effect of water touching the probes in NI MultisIM. How I can model the real
water properties effecting my probes

Q.3 any other idea to achieve the task?

waiting for reponse

regards

ultrasonic transducers are the best for the job,secondly,i use proteus for it but the problem that you will face is to simulate the water level thats basically done by providing analog values to the input randomly. THERE IS NO OTHER WAY TO SIMULATE WATER LEVEL ,i suppose.

thanks

ultrasonic sensors should be placed at top somewhere where water level is to be observed.
water vaporization and hydration effects may introduce errors in sensing ( transducer may have contaminated vapor deposits)

I want a robust, reliable, error free, sensing system which I install and forget.

this sensing mechanism is at initial experiments, I will convert it to microcontroller with many variables to be watched once the sensing part is over.

for Water Modeling and level simulating in any simulator, I am GNDing the probes by a switch for the presence of water, that is OK.
but how can I model the real properties of water conductivity, capacitance (if applicable) or other characteristics involved in stored water which can come in effect to my sensing probes

sunnyimran said:

Hi all,

I am working on an electronic water sensing mechanism.

In an underground water tank I need to sense various levels of water as the water level is consumed and refilled. Later I want to control the sump motor with logic when various conditions are met.

focusing on just electronic sensing mechanism there are many choices available

- biase a transistor with the help of water as conductor
- use Logic gates inputs to become HIGH/LOW when water touches probes.
several choices for gates, any gate can be used in general, even a NOT gate can do.
- Ultrasonic depth sensing.
- LDR based
- various other.

I am working with logic gates at teh moment but will transfer it to microcontroller later when I am satisfied with 'water sensing'
the problem with many techniques above are, their reliability changes with many environmental effects. water vapours, hydration, corrosion, electrolysis, temperature and many similar factors change parameters which can affect changes in sensing.

currently I am working with NAND CD4093. it has built in schmitt trigger so it can shape inputs.
I am prefereing to give oscillated inputs to this logic gate, so at least electrolysis can be prevented. probes will be usually dipped in water.

To perform oscillation in sensing probe I can use transistors ( ac biased), 555, opamp.

Q.1 which one would be better option for oscillating in this scenario?

Q.2 How can I simulate the properties of tap water in reservoir e.g. water conductance and other electrical properties in NI multisim?
currently I GND the inputs with a switch to give the effect of water touching the probes in NI MultisIM. How I can model the real
water properties effecting my probes

Q.3 any other idea to achieve the task?

waiting for reponse

regards

Click to expand...

There are several methods useful to detect water level in a tank. You can choose a low-cost one or quite expensive, as follows:

- a contact driven by a floater. A plastic-foam ball , or a ping-pong ball is the floater. Mounted on a lever or on a magnet drives a sealed contact, or a reed switch, to indicate water level above a selected limit. Several such sensors can be mounted in a tank. Safe, low-cost, and reliable.

- an ultrasonic sensor is commercially available, to measure distance to sound-reflecting level. The advantage is that it can be mounted on the top of a tank. Disadvantages are: wavy water level disturbs its function, reflections of ultrasonic waves from tank walls can generate fake readings, corrosion can cause a failure. Moderate cost.

- a microwave "radar" sensors are available, some need "antenna rods"down to the tank bottom, others operate without it. Precise, reliable, high-cost.

- another low-cost solution is to measure water tank weight from outside, e.g. by a tensometer or weight sensor mounted on a support. Often the best solution.

Q1. The best oscillator design is one that you are able to understand and apply to your requirements. Any of these can work. Some commercial conductivity sensors are simply using 50 Hz AC low voltage from a transformer, by the way.
Q2. In the present regard, water can be simulated as a variable resistance (presuming you are using moderate frequencies), think about kohm range. Commercial conductivity sensors often have adjustable threshold, e.g. 1 - 100k.
Q3. Besides the mentioned sensor principles, hydrostatic pressure is quite popular, e.g. immersion pressure sensors for tanks.

Hi.
How many points of level detection do you want ?
3? ---Full, half, empty; or more points in between ?
Or analog infinite ?
What is the difference in depth from full to empty ?
At what depth below surface ground is the tank bottom ?
How much reliable and lasting do you want it to be ?
Will the level reading control a water pump motor or will do other things ?

Externet said:

Hi.
How many points of level detection do you want ?
3? ---Full, half, empty; or more points in between ?
Or analog infinite ?
What is the difference in depth from full to empty ?
At what depth below surface ground is the tank bottom ?
How much reliable and lasting do you want it to be ?
Will the level reading control a water pump motor or will do other things ?

Click to expand...

I want 8 points of level detection
each point is one foot higher than previous one.

from full to empty, the difference is approx is approx 10 foots. this is an underground tank of concrete.

I want it reliable and long lasting, free from errors and safe from enviromental changes. a one time install solution, no corrosion at probes, no electrolysis, no
reading errors due to temp changes, hydration, vaporization, ...................

Tank bottom is approx 10 foots

level readings at the moment will only light up LED's but at the next phase they will be the inputs to a micro controller based logic algorithm implementation where two pumps will be in service in parallel but one at a time, next time next up, will take turns. several conditions will be checked to turn the right pump, or to just give warning beeps. and more ....... but this all will come in next phase, later.

- - - Updated - - -

I understand all three oscillators I mentioned, AC biased transistors, 555 clock generator, OP AMP generating square waves.
I want an oscillator which will oscillate in +ve and -Ve polarities, this scheme can avoid electrolysis.
I think OP AMP will do that better.

now how to make the reading from probe non-oscillating so that it can be fed to a logic gate, otherwise logic gate output will also oscillate.
should i use de-bouncing before giving input to logic gates

Are there any stray capacitive/inductive or other parameters in tap-water other than the conductance ( or resistance) that should be taken care considering digital inputs?

I am trying to avoid any commercial sensors. I prefer building my own.

bro i have been using it for approx 6 months uptil now,and it hardly cost 200rs,whats the difinition of robust,its true it has vapours but it wont damage ur transducer,as its a crystal and i dont believe sound could be immensely affected by vapours. 2ndly grounding the probe is not a robust technique in a month or two it will get corroded or a layer might get deposited over it which will alter the functionality of your schema.

Usama Siddiqui said:

bro i have been using it for approx 6 months uptil now,and it hardly cost 200rs,whats the difinition of robust,its true it has vapours but it wont damage ur transducer,as its a crystal and i dont believe sound could be immensely affected by vapours. 2ndly grounding the probe is not a robust technique in a month or two it will get corroded or a layer might get deposited over it which will alter the functionality of your schema.

Click to expand...

All right I will keep sound transducer in consideration. my tank is cover sealed in normal usage so lot of hydration and vaporization exists at top of water level.

can you share design idea for transducer based sensing?

thanks

I would stick to an industry proven reliable method. If you prefer to build the sensors yourself, well, gather the parts and replicate these magnetic reed sealed switches :

http://i00.i.aliimg.com/photo/v0/405215382/Mini_Float_Switch_plastic_type_.jpg

and an example supplier: http://www.deeterelectronicsinc.com...es-vertical-liquid-level-sensors-float-switch
should be available at your location, at industrial supplies.
Eight of them nested inside a ~1" PVC pipe, and a second 1/2" pipe glued/clamped next to it carrying the wires to the outside, to a tiny 8 led array like this :

http://www.jameco.com/Jameco/Products/ProdImag/789961.jpg
-------------------------------------------------------------------------------------
A second way is using a 8 feet long 1/4" open-bottom pipe vertically inserted in the tank attached on top to one single inexpensive automotive pressure sensor which provides an analog voltage output and a LM3914 to drive the same LED array :

http://www.allpar.com/fix/codes/sensors/MAP.html

Available for nothing at wreck yards.

I tested a "Craftsman" low-cost ultrasonic distance meter, also to detect water level in a tank. It works well until the level is disturbed by waves. If your water tank has no waves on water, ultrasound can be used. The device, however, is designed as a pocket instrument for construction workers, with a range of ~10 meters max. For a long-term use on a water tank, you will have to make it (or the sensor) water- and corrosion-proof.

As I wrote, I used the ping-pong-ball driven reed switches in a water well level sensor. It is corrosion resistant, very reliable, and very low-cost. It has worked for more than 15 years, and I think it still works, no maintenance, no failures.

jiripolivka said:

As I wrote, I used the ping-pong-ball driven reed switches in a water well level sensor. It is corrosion resistant, very reliable, and very low-cost. It has worked for more than 15 years, and I think it still works, no maintenance, no failures.

Click to expand...

good to hear 15 years in operation for reed switches.

what's do you say about hall-effect IC sensors in place of reed switch fixed at many level marks inside a pvc pipe, while a floating circular magnet (permanent magnet) running through pipe length. this way no terminals exposed to water.
but yeah sometimes floating magnet may stuck up on pipe.

that floating

sunnyimran said:

good to hear 15 years in operation for reed switches.

what's do you say about hall-effect IC sensors in place of reed switch fixed at many level marks inside a pvc pipe, while a floating circular magnet (permanent magnet) running through pipe length. this way no terminals exposed to water.
but yeah sometimes floating magnet may stuck up on pipe.

that floating

Click to expand...

Please try what you want; I recommended what I did and I had the vest experience with simple solutions.

A multi reed switch + single floater design is often used for quasi continuous level measurement with analog output (potentiometer circuit). I think it's a good solution for clean liquids, e.g. water tanks.

I was thinking of OP-AMP as LOGIC producer, I realized OP-AMP is an analog device. Reason to utilize was that I needed some tolerance at inputs of a logic gate. Later I relaized that a schmitt inverter such as 74HC14 can provide tolerance at input because of built in schmitt.

Now if considering water conductivity to make a logic’s input to LO or HI I have following considerations:

- Use ACTIVE LOW OUTPUT SCHMITT INVERTER ( such as 74HC14)


NOTE: water conductivity at input of the inverter makes the input LO to make the output HI



- Use NAND with Schmitt inputs such as CD 4093 but make it a NOT gate by shorting the two inputs together


NOTE: water conductivity at input of the NAND makes the input LO to make the output HI


Q. What difference can it make in above two scenarios if I use inverter Vs if use NOT-GATE based on NAND both have Schmitt?

VS


Q. should use CMOS or TTL family? Which would be better suitable

Q. what supply rating devices would be better. These devices are available in 5V and higher ratings. Higher voltage rating device like 10V ( series 4000 and 74C00) their input will have more margin for voltage levels. So a slightly larger current we can pass through water probes so I think that would be better with contaminated probes.


Q. Also need to consider the length of wire from sensor probes to circuit is approx. 10m and it may pick noise in between. It will pass nearby the electrical water pump. I am thinking of using CAT5 ethernet cable for this purpose, it is readily available and has cross twisted pairs. I think therefor, AC signals would be better than DC because DC LO/HI can be fooled easily if my wire picks noise.


Q. In Multisim what is the difference between Vss and GND and Digital GND ? I used GND only and it works for all CMOS devices. is it necessary to use VSS also?

It's not clear to me what you want to achieve now. As previously mentioned commercially available conductivity based level switches are using AC resistance measurement with an adjustable threshold in 1K to 100K range. It can be made in different ways, e.g. using CMOS ST or OPs for oscillator and threshold detector.