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TerraMex · 04-30-2003, 01:21 AM

I've found a way to maitain a similiar schematic (see Jsimmons first post) but not having any metal contact with the water.

The trick is to replace those contact points with a thermistor. Connecting the thermistor to a powered wheastone bridge can ajust the output level, and still connect to the switches. This type of system is called a Hot-Wire type measurement. It is supported by the fact that the thermistor in the water is hotter than the one above the water level. Or in cold water, cooler than the ones outside.

However it can be tricky to ajust. The water in a WC system is at room temperature with everything off, it warms up to a few degrees when the pump starts and when the pc is powered it (in average) stabilizes after a few hours at a given temperature depending on the system. Not knowing how sensitive is those logical gates, i cant really say if it would work with a oscillating voltage. I can however, be filtered or even attached to a regulator (see OpAmp basic circuits), but that will certainly boost the cost and complexity.

Another thing is displacer switches, wich are actuated with the connected floater operates a spring. Havent found much literature about it thou.

@ BigBen2k

>You can use a float (plastic) in a tube, and detect its position >with the IR sensors.

I've seen some problems with that . The actual big problem is that you need a good deal of area to bounce off the IR . It's easy to think that you can have an emittor and a receiver next to each other in a small tube but they generate interferance with each other, making that arrangement a faulty one. It does work however with ultrasonic measuring devices.

It can work having a emittor and a receiver at each top upper "corners" of the deposit (opposite), with 45º (ajustable) aimed at the surface of the water. The drop of level will alter the reception of the IR signal to lower points, thus giving a good measure of the water level. I've also seen a that type of measurement , i'll see if can post some diagrams today. Cant find any decent link on the web, but i have access to a few control and instrumentation books at school.

04-30-2003, 01:21 AM	#24
TerraMex Cooling Savant Join Date: Nov 2002 Location: Portugal, Europe Posts: 870	small update. I've found a way to maitain a similiar schematic (see Jsimmons first post) but not having any metal contact with the water. The trick is to replace those contact points with a thermistor. Connecting the thermistor to a powered wheastone bridge can ajust the output level, and still connect to the switches. This type of system is called a Hot-Wire type measurement. It is supported by the fact that the thermistor in the water is hotter than the one above the water level. Or in cold water, cooler than the ones outside. However it can be tricky to ajust. The water in a WC system is at room temperature with everything off, it warms up to a few degrees when the pump starts and when the pc is powered it (in average) stabilizes after a few hours at a given temperature depending on the system. Not knowing how sensitive is those logical gates, i cant really say if it would work with a oscillating voltage. I can however, be filtered or even attached to a regulator (see OpAmp basic circuits), but that will certainly boost the cost and complexity. Another thing is displacer switches, wich are actuated with the connected floater operates a spring. Havent found much literature about it thou. @ BigBen2k >You can use a float (plastic) in a tube, and detect its position >with the IR sensors. I've seen some problems with that . The actual big problem is that you need a good deal of area to bounce off the IR . It's easy to think that you can have an emittor and a receiver next to each other in a small tube but they generate interferance with each other, making that arrangement a faulty one. It does work however with ultrasonic measuring devices. It can work having a emittor and a receiver at each top upper "corners" of the deposit (opposite), with 45º (ajustable) aimed at the surface of the water. The drop of level will alter the reception of the IR signal to lower points, thus giving a good measure of the water level. I've also seen a that type of measurement , i'll see if can post some diagrams today. Cant find any decent link on the web, but i have access to a few control and instrumentation books at school. __________________ "we need more cowbell."