I'm a plumber and I'm not able to find a commercial product that fits my needs, so I'm wondering if it would be feasible to build it from scratch... I'm familiar with basic understanding of electronic circuits, but cannot find an answer by myself.
I'm designing a heating system powered by a fireplace, and a big hot water tank to store heat for use when fire is off. Heat will be usable in the 55-80°C range, and the water is expected to be fairly well stratified, so temperature sensors placed at different heights would give a good figure of the energy content of the tank.
When fire is on, boiler will push water at 80°C into the top, so the tank will start to "fill up" from top to bottom. When water at this temperature reaches, let's say bottom quarter, the operator needs to be warned that the tank is "full" to stop feeding the fire. If water at 80° reaches the bottom, water out of the boiler will be at a higher temperature, which is undesirable.
On the other hand, when the fire is off, the heating circuit will push water at about 60°C into the bottom. When all water in the tank is at this temperature, it is "half full", and it will take this water again down to about 45°, at that time the tank is "empty". The operator should know the amount of usable energy in the tank with a look to plan lighting the fire again.
So, I need a way of displaying the measurements of the sensors in an easy to read form, accuracy is not important. I was thinking about converting it to a voltage that could be shown by an analog voltmeter with a custom drawn scale, but I have no clue how to sum up the results of the multiple sensors. Other suggestions are also appreciated. The system just has to be easy to implement, reliable and easy to read.