Measuring water level (help!)

[sigve]

Hi

I have buildt a radio controlled car out of four bottery opperated drilling machine (looks realy cool) I have mounted some lights and a water canon, and done all the electronics my self. the next thing I want to mount on it is a way to measure the water level in the water tank (and eventualy send it back to my transmitter by IR) The Question is how do i measure it what cind of sensors are there, I know about Capasitiv (Or however it is written :confused: ) but they are so expensive, i need thre outputs (levels) to make it compatibel with the rest of the elektronics.

Thanks for all help

Sigve
sigve@hotmail.com

[sesat]

http://www.freescale.com/files/sensors/doc/app_note/AN1950.pdf
http://www.freescale.com/files/sensors/doc/app_note/AN1516.pdf


Ram.

[Acetronics]

:)
Hi,Sigve

There's a very simple way to measure it, if you do not want too a precise scale ...

use your tank ( plastic, of course !!! ) as a condensator; you just stick two thin copper sheets ( used for RF protection inside metering electronics ) on the top and the bottom ( all the surface ) and use it as an 8 pins PIC clock capacitor ( RC Osc, of course ) ...

Just compare the Osc freq to values mesured with precise contents ... that's all !!!
And it is already sold as a Fuel gauge for Methanol engines ...by LLM Electronics ( France ) !!!

Hé, Hé !!!

Another use is metal detector ... here, metal presence changes the coil value, and the osc freq ...

Think simple !!!

Alain

[Comatose]

Depending on the size, anotherway to go might be a float (piece of styrofoam) on a shaft (piece of balsa) with a spring (rubber band) which has a potentiometer on one end. As the water level falls, the potentiometer will rotate, giving you capacity.

[Arp]

You could put a pressure sensor on the bottom of the tank.

I have seen ready-made fluid pressure sensors sold in bigger component stores, but how they indicate their reading (voltage? resistance? frequency? TTL serial interface?) I cannot tell.

[sigve]

Thanks for all the help.
The pressure sensor sounds like a good idea
Alain i did not understand your idea completly, but is it somthing about changing the capasistans of the "condensator" with more ore less wather :confused: and what is that about an 8 pin PIC :confused: .
How about a system with a LDR in the botom of the tank and a led in the top (the tank is not transparent)?

Sigve
sigve@hotmail.com

[j8m8l]

How about two wires which are shorted when the tank is reaching a minimum level. You could use a potential divider and transister to get it all tuned up. Really simple but could do the job!

Josh

[lazy-b]

Alain,

Yes, I have one of those Fuel Level Indicator made by HIROBO, they have one electrode connected inside the tank, and a copper plate attached on the side of the tanks, the two wire goes thru a MatchBOX size module where there is a trimmer that you can adjust the mininum fuel level to activated the LOW FUEL INDICATOR thru flashing LED.

I guess, they use one electrode always submerge to fuel to maximize capacitance reading.......I like the idea of using a TWO copper plate only, this will avoid putting an electronde in the fuel.

Guys: you might what to experiment this, using a CAPACITOR TESTER, attached the two copper plate on the 2 opposite side of the Fuel tank, and connect the two copper plate to CAPACITOR TESTER, filled the Fuel Tank and you read the CAPACITANCE as you fill it......I guess it very very small, I even not sure if it can be detected by the Capacitor tester........I guess you have to use a Fuel Tank with a thinner plastic walling.

Been using this Fuel Tank Indicator on my Scale Helicopter, but later find its not reliable, have to constantly recalibrated the fuel level....I did not use it any more, Its more reliable to use TIMER, just set the TIMER for 10 minutes average flight.

But, for simple Water application, I guess a simple Float attached to a micro-switch, as suggested by other will do the job.

[Acetronics]

[QUOTE=sigve]Thanks for all the help.
The pressure sensor sounds like a good idea
Alain i did not understand your idea completly, but is it somthing about changing the capasistans of the "condensator" with more ore less wather :confused: and what is that about an 8 pin PIC :confused: .

Hi, Sigve

The value of the capacitor depends on what is between the electrodes ... methanol, water, air ....

The pic has its clock oscillator working with an RC combination; as C is very small ( ~ 20 pF to nF ) the capacitor can be your tank with its electrodes ...

Hi, Lazy - B

The electrode inside your tank gets dirtyand full of oil , may be oxydation on the electrode ( methanol Ph can reach a value of 2 !!!) ... just try the second electrode outside the tank.

The float is the simplest ... but must enter the tank !!!!

best regards
Alain

[lazy-b]

Alain, Yes, your right, the electrode gets dirty. thats why I do not use it any more......I guess the new version that you mention is more intelligent.

Been thinking of using a Magnetic Float...put a small magnet in a float, the the float is inside the tank....using a linear hall effect sensor, to sense the position of the float....I guess this look better....for more simple circuit, you might use a simple reed-relay instead of using a Hall-effect.

Ellion

[sigve]

hi

is it possible to sense the cunductivity of water. maby use two copper rods that are very close to each other to sense if there is wather ore not?

[Acetronics]

:rolleyes: Hi sigve

Seems you just want to know if there's water ...

Then very simple too : there is a pump somewhere ... place a diff pressure sensor between input and output: If there's diff pressure, there's water.

That's all.

Alain

[sigve]

no I want to know how much there is in the tank, and was thinking of using three or four sensors in different hights in the tank (one on tob, one in the middle and one on the botom). or maby one analog measuring divice for the whole tank.

[Fluid-Druid]

Sigve
I've seen a circuit that was used on a model train that used three stainless
steel electrodes fixed into the backplate of the boiler via p.t.f.e. insulators.
This was connected to a transistor circuit (it was years ago) that relied on the
impurities of the water,the boiler was the earth connection.this caused one of three
leds to light according to the water level,It could be done with op-amps now,but you
would have to have a copper strip in your tank if it is made of plastic.However
if the water is splashing around it will cause erroneous readings,the train didn't
jump around so not a problem! :)
So you could have a tube on the side connected top and bottom of the tank,with small
inlet aand outlet then the level will not jump around so much.and use opto slot sensors
arranged up and down the tube you may be able to detect the level. :confused:

Mike

[william541]

Sigve,

The stainless probes do indeed work and yes there needs to be minerals in the water to make it work properly. Typically you make a resistor divider with the center of the divider connected to either the base of a transistor or even a 74HC04 inverter input. Use the analog HC04, and not the schmidt trigger HC14 because of the hysteresis. One end of the resistor divider gets attached to your pulse source and the other gets attached to your tank probe.

On your tank, you need a measurement probe (attached to the resistor divider) and a common or ground probe. Place the two probes horizontally from each other so they both get submurged at about the same time, or place the ground probe lower. The spacing can be adjusted for sensitivity. Typically 1.5" to 2" between probes works well. You can use as many probe pairs as you want for different levels.

How the circuit operates is that the two resistors plus the resistance of the water make up a voltage divider. If there is no water present, the transistor or 74HC04 will be forward biased and turn on. If there is water present, the voltage at the center of the divider will get pulled low by the resistance of the water and not turn on the device.

Keep in mind that you need to apply a short pulse to the probes during the measurement. The reason for this is that the probes will corrode very fast if you just applied straight DC all the time. The down fall to this system is when you get mineral build-up on the probes and tank walls, then moisture will look like there is water when there really isn't.

The pressure sensor also works with very high resolution, I have made systems that measure in mm of water column. The thing about using pressure sensors is that you need to use a differential sensor. The differential can be between atmospheric pressure and water pressure at the bottom of the tank. When using atmospheric pressure, you need to make sure the tank is well vented. You can also use a closed system where you have two wet ports on the sensor. One port is attached to the top of the tank and the other to the bottom. The pressure differential is your fluid height. The wet port, dry atmospheric port differential sensors are easier to get working properly and the sensors are less expensive. The sensors need to be very sensitive, as it takes about 27" of water column to equal 1 psi. So short tanks are harder to design for than tall ones.

Have fun with your project! -Bill-

[sigve]

Hi William and fluid-druid

I think il try that system, I will just mount the probes with screws so they are easy to take out and change if they corrode.

Thanks everybody for all help.

Sigve
sigve@hotmail.com