I'm in the middle of upgrading my espresso machine with some blown electronics with external sensors and new control logic, I'm stumped on performing the water level calculations, as the machine did not come with a water level sensor.
It's a single boiler which pressurises upto steam temperatures at a higher pressure, letting water out as steam until the boiler is low and the element exposed, or the boiler isn't completely full before heating, which would result in more cold water entering the boiler than I'd like. Either way, I'm stuck coming up with a reliable method of detecting the water level without modifying the boiler as its pressurised.
The boiler is attached to a metal frame and leaves little option for resistive sensing, but I think that there might be room for capacitive sensing. If I had a probe attached to the boiler, could I measure its capacitance to see if it's full or empty. As water has capacitance, I can use a capacitive touch sensor to detect the change in capacitance in the boiler. Does the capacitance of water change with temperature?
I'm also thinking of adapting the Touche swept frequency sensing Touché with Arduino | Arduino Blog as a method of detecting the state of the boiler. It's really the capacitive sensing running a swept range of PWM frequencies, as the capacitive profile changes with the charge, so I can get more detail than regular touch sensing.
Does this sound viable to go forward with? I'd love to hear any other ideas on how to do this without opening the boiler.
I don't exactly know what your goal is here. Sense water level, why? Are you wanting to turn off the heating elements when the water gets low?
Give us your goal, and how you think you can accomplish it please.
The reason that got me started looking into the water level sensor was a low level cutoff. As the water escapes the boiler as steam, the water level drops and will need to be replaced by the pump, however the boiler is sealed and only has a thermistor sitting inside. The amount of water lost as steam is unknown and I'm not willing to modify the boilers integrity by installing probes.
The goal is to detect if the water level is low in the boiler as a safety shutoff, or to redirect more water to the boiler before that's needed.
I'd also like the ability to detect the water level inside the boiler so I can fill the boiler before heating. As an unknown amount of water leaves through the steamer, I can't simply enable the pump until it's full without getting feedback that it's full.
I think I can accomplish it through capacitive sensing, sending a pulsed signal through a circuit, using the capacitive properties of water, the capacitance should change as the water level changes. I can record the data from several data points and see how the results change as I empty, fill, heat and pressurise the boiler.
I'm still new to capacitive sensing and would love to know if it's a bad idea before I embark on it. I'm safe on the pressurised, heated end of the boiler as the overflows are tested and work, but I need to know if the tank is dry first.
I assume the boiler is a metal enclosure, of some size. I can't imagine being able to get a capacitance reading of the water inside, by testing outside.
A couple random thoughts. I still don't know the setup, so these may not apply depending on that.
Test the weight of the boiler.
If the thermostat connects to the outside, can you repurpose those wires to send the water level outside.
Put a sensor on the output "water escapes the boiler as steam". test for pressure, moisture, or heat. That should tell when the water has been used up.
A couple random thoughts. I still don't know the setup, so these may not apply depending on that.
Test the weight of the boiler.
If the thermostat connects to the outside, can you repurpose those wires to send the water level outside.
Put a sensor on the output "water escapes the boiler as steam". test for pressure, moisture, or heat. That should tell when the water has been used up.
[/quote]
Agreed. I'm working with pressurized steam and the best way to control your feedwater timing is by monitoring the pressure change on the output. As the water in the boiler is depleted, the pressure drops.
Also, depending on the placement of the thermistor, you could use the temperature change caused by the fresh (cooler) water hitting the thermistor. If the placement is close enough, it would be simple. If the placement is a little low you can adjust with a delay before shutting off the feedwater pump, (delay=volume needed / pump flow rate) and so on.
Also, if anyone has any leads on high pressure sensors that can take some heat, please let me know.
Cheers