I am attempting to develope a simple circuit to detect the presence of water (tap water) in a tank. The idea is to use two stainless steel probes with one connected to circuit ground and the other stainless steel probe connected to a 5 VDC source through a current limiting resistor (about 4.7 mΩ resulintg in current less than one µA to keep the total circuit consumption low enough to operate from a 9 volt battery for at least one year). With one of the probes out of the water there will be no current flow and the voltage should be at or very near the 5 VDC level. With the probes in the water the voltage seems to run from about 0.5 to 1.9 volts. I planned to use a CMOS inverter to detect the voltage change when one (or both) of the probes are out of the water. Unfortunately, the lower worst case threshold voltage useing a 5 VDC supply is below the 1.9 VDC. However, I can use a comparitor set at say 3 VDC to detect when the water level drops below the probes. Here are my questions since I am certeinely not an expert with electrolysis and water detecion.
1. The tank capacity is bout 5 gallons with the water level never above 2 gallons at room temp. The tank is not sealed so I am not concerend about any hydrogen gas build up. However at 5 vdc at less than one µA I can't believe that the hycrogen/oxygen productions would be significant?
2. I have read that stainless steel probes work well and should not rust. Looking to use V4A stainless steel. Is this a valid assumption?
3. Not sure why there is a slow build up of voltage across the probes when they are in the water. Can someone enlighten me on this phenomona? If the voltage can build up to my set detection voltage than I am in trouble?!
4. I have seen information indicating that they use AC to avoide electrolysis. Is this just to avoid the build up of gas or is there some other reason why they want to avoid electrolysis?
Any help is much appreciated!! Thanks in advance!!
1. The tank capacity is bout 5 gallons with the water level never above 2 gallons at room temp. The tank is not sealed so I am not concerend about any hydrogen gas build up. However at 5 vdc at less than one µA I can't believe that the hycrogen/oxygen productions would be significant?
2. I have read that stainless steel probes work well and should not rust. Looking to use V4A stainless steel. Is this a valid assumption?
3. Not sure why there is a slow build up of voltage across the probes when they are in the water. Can someone enlighten me on this phenomona? If the voltage can build up to my set detection voltage than I am in trouble?!
4. I have seen information indicating that they use AC to avoide electrolysis. Is this just to avoid the build up of gas or is there some other reason why they want to avoid electrolysis?
Any help is much appreciated!! Thanks in advance!!
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