fluid sensor circuit

[sam12345]

I would like some help in designing a sensor circuit (using Darlington transistors?, may be two in series?) that would with couple of probes in a plastic container sense the presence of a non H2O fluid or lack of it. Lack of fluid then would trigger couple of LED s. I have to use ~8 V (1.2V X 8) cells to accomplish the task. Any help is appreciated.

 

[grim]

if the fluid conducts, then just drive the base current through the liquid.

 

[Leftyretro]

I would like some help in designing a sensor circuit (using Darlington transistors?, may be two in series?) that would with couple of probes in a plastic container sense the presence of a non H2O fluid or lack of it. Lack of fluid then would trigger couple of LED s. I have to use ~8 V (1.2V X 8) cells to accomplish the task. Any help is appreciated.

You really need to be more specific about what the "non H2O" fluid is. What is it's conductivity specification?


Some liquids like oil are very good insulators and a current sensing contact type level sensor might not work reliably.

Lefty

 

[Wingmax]

I would like some help in designing a sensor circuit (using Darlington transistors?, may be two in series?) that would with couple of probes in a plastic container sense the presence of a non H2O fluid or lack of it. Lack of fluid then would trigger couple of LED s. I have to use ~8 V (1.2V X 8) cells to accomplish the task. Any help is appreciated.

Do some experiments on measuring the resistance of the fluid. Use this resistance as a resistor to bias a transistor. Use another resistor on the base if necessary to adjust to turn the transistor on or off if the fluid is present.

 

[grim]

or a float switch

 

[Wingmax]

if the fluid conducts, then just drive the base current through the liquid.

Hope the fluid is not highly flammable.

 

[sam12345]

Hi all
Thanks for your time and info.. The fluid that I have in mind is model engine fuel which does contain oil. I know that it will not conduct current as good as water, but it does conduct some current. This is why I need to amplify the current to activate a 5V relay that will light couple of LEDs. Since I am limitted to using 9.6V nicad pack as power source, which Darlington would you recommend for high amplification of the current that will pass through the fuel? Any one brave enough to draw me the basic schematic? Thanks
Sam

 

[jpanhalt]

Hi all
Thanks for your time and info.. The fluid that I have in mind is model engine fuel which does contain oil. I know that it will not conduct current as good as water, but it does conduct some current. Sam

I suspect the conductivity of model aircraft fuel changes with conditions and source. If you are referring to "glow" fuel, I would suggest a capacitance-based method as has appeared on this site several times. One recent discussion was:

https://www.electro-tech-online.com/threads/liquor-level-detect-via-computer.33273/

Scan down to the post by KMoffett, which includes a schematic. Capacitance probably changes with the fuel composition as well, but capacitance is a well established means for measuring fluid levels. John

 

[KMoffett]

John,

Thanks for pointing to my circuit. I would have done that earlier, but Sam's original spec's (8v battery and a darlington) almost sounded like a school assignment.

Sam,

My circuit was to monitor for an empty plastic fuel line from an aircraft's overhead fuel tank. It could also be used with a plastic "sight tube" outside a container. I just measured some kerosene and naphtha, and got infinite resistance. So, it looks like it's possible to just use two metal probeds directly in the fuel container. Since capacitive sensors are affected by their surroundings, can you describe in detail were and how this "plastic container" is used?

Ken

 

[sam12345]

fluid sensor

Hi one and all
Thanks for showing an interest on my thread. Basically what I have is a 25 ounce plastic container that is filled with model aircraft fuel and located in the fuselage of an RC heli. Normally, to keep track of fuel consumption and prevent fuel starvation, you would reset a clock on your transmitter and fly the thing for so many minutes before landing it, usually 10-12 minutes affair depending on the size of the fuel tank.
What I am trying to do is design a circuit that would have enough current amplification with 9.6 V pack to overcome the resistance of the fuel. I was successful using a 15 V from a DC power supply, but the added weight would jeopardize the flying characteristics of the helicopter. The question is , what transistor would have a very high gain and operate on 8-9v dc?
ty all
sam