Circuit to trigger an alarm on water level change

I have a water tank where I want to get an alarm when the water level change, up or down, based on to wires going from top to bottom in the tank as sensors. I have found a circuit on the web to trigger alarm on a certain water level, but not one that triggers on change in water level. I want the circuit to be simple with as few components as possible more that accurate. I also have living organism in the tank so the voltage on the sensors to be as low as possible. Can anybody point me in the right direction? Than you.

Reply to
ove
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On a sunny day (Fri, 03 Aug 2007 02:06:25 -0700) it happened snipped-for-privacy@touchsoft.no wrote in :

Pressure sensor in bottom, PIC

Reply to
Jan Panteltje

I forgot to say that that prssure sensor is not an option, I need to use two paralell wire sensor. - Any idea? Offa

Reply to
ove

Why?

Reply to
Bruce Varley

snipped-for-privacy@touchsoft.no

How about putting a square wave signal ( IC555 ) on the bottom wire and monitoring then other wires with a PIC processor.

Keith

Reply to
Keith Sloan

How fast is the change? Would it be ok if the system ignored very slow changes?

Signal --> High Pass Filter ---> Window Comparitor

If you need it to react to even very slow changes, the high pass filter can be a bit of a problem. If yu don't want to use a PIC, you can use a DAC and a counter.

Reply to
MooseFET

snipped-for-privacy@touchsoft.no wrote in news:1186131985.940453.214720 @g4g2000hsf.googlegroups.com:

You have two tasks.

1: Get a linear electronic value of the level in the tank.

2: Sample the signal collected in step 1, and compare with a previous sample. Based on the outcome, you would have a signal of a change in either direction, or a stable value.

Reply to
Gary Tait

It doesn't truly have to be linear.

Reply to
MooseFET

Jesus just weigh the damn thing.

Reply to
a7yvm109gf5d1

On a sunny day (Fri, 03 Aug 2007 07:50:42 -0700) it happened snipped-for-privacy@netzero.com wrote in :

But Jesus walked on water, so things may happen.

Reply to
Jan Panteltje

Probably because it's a homework question!!!

The OP hasn't said whether the 'organism' lives in fresh or salt water. That makes a huge difference to the sensitivity of a two-wire sensor. How about a float running up and down the two wires with a linear Gray code graticule attached. I guess it depends on how much space there is above the tank. Ah, his supervisor won't have thought of that method will he.

--
John B
Reply to
John B

snipped-for-privacy@touchsoft.no

Capacitive sensor on outside of tank. I'm assuming glass or plastic walls.

--
Paul Hovnanian	paul@hovnanian.com
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Reply to
Paul Hovnanian P.E.

Change in water level...like from rain, leaks and fish jumping out...

So call it level A and level B and A-B is the water level change.

So... I guess the circuit sets Level A to be at the water surface..

But the level A set point should change so that a difference can be monitored beginning at any tank level.

| | | Level A | |\\/\\/\\/\\/\\/\\/\\/\\/ water | Level B | | |_________________ D from BC

Reply to
D from BC

If you have access to the outside of the tank, use a sightglass with a ball and an array of optical sensors?

A pressure sensor at the bottom?

Sonar?

Good Luck! Rich

Reply to
Rich Grise

snipped-for-privacy@touchsoft.no

Use platinum wire, and have a reference sensor to tell you the conductivity of the fluid in general. Then just measure the resistance.

Good Luck! Rich

Reply to
Rich Grise

On Fri, 03 Aug 2007 02:06:25 -0700, ove wrote: ...

How do you intend to account for movement of the critter?

Good Luck! Rich

Reply to
Rich Grise

use insulated wires and measure the capacitance between them (perhaps use 0.1" pitch ribbon cable and measure between odd and even numbered conductors

what counts as a change in level?

Bye. Jasen

Reply to
Jasen Betts

I have done some measurement on the sensor and found that the resistans is from 200Ohm to 1KOhm. I need to have a trigger if it drops 50 Ohm within 10 sec. time. - An increase in ohm is not important after all. I also cheked that I can use a measurement voltage of up to 1,5V without disurbing the living organism.

Anybody have an idea of a simple circuit, without too many components, that can solve this?

I found a circuit on the Velleman web that may be used as a starting point.

formatting link

Offa

Reply to
ove

I don't know what's best for your incompletely described situation. You need some kind of precision to detect 50 ohms out of 200 to 1000. LEDs make good voltage references. You could do something like this with a "dual single supply" operational amplifier. Select R1 for about 10mA through a 1.5V red reference LED: View in a fixed-width font such as Courier.

. . . V+ . | . +-----------------+--------|--+--[100k]------------|-\\ | | . red --- .---|-/ | | | >--+--> | | . LED ~ \\ / | |/ [51] .----+--|+/ | -- -- . 1.5V --- | | | |+ |/ | . | +----o o-+--[100k]----' === [100k] . | | || |47u | . | [1.5k] Rx +--------' . | | | . | | [10k] . | | | . '----+-------------+-------------' . | . --- . gnd . .

Reply to
Fred Bloggs

Never mind, I don't like that circuit, it has practical problems...

Reply to
Fred Bloggs

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