Maximum Overhang?

[amoose136]

Why not stick two long copper probes close together and held vertically in the water and then measure the resistance? It should drop as an inverse function of fluid height as the resistivity of the salt water should be constant if it doesn't heat up too much from the resin hardening (which is exothermic) but the fluid wire crossection would be a linear function of height.

[Synchron]

Why not use the laser and a floating mirror on the resin. Messure the time, the laserlight needs to a sensor.

[Synchron]

(sensor)
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/ (semitransparent mirror) - - - - (laser)
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_ (floating mirror)

[jsondag]

I think a capacitive sense would work best. Resistance is relative to salt concentration, and would require re-calibration every time. I could easily rig up a test with an arduino. you just need to tape a conductive strip to the outside of the container vertically, and submerge a corrosion resistant lead into the water. Gold coated PCB trace would be ideal, and cheap/easily salvageable. You can measure the capacitance which should increase linearly as the water level rises. You can measure it with an arduino using 3 pins, and two resisters, or using a 555 timer, to generate a digital modulated output which could be measured by your drip input on the peachy.

[CescoAiel]

Why not use the laser and a floating mirror on the resin. Messure the time, the laserlight needs to a sensor.

Hardest there would be to maintain the floating mirror's position!

I think a capacitive sense would work best. Resistance is relative to salt concentration, and would require re-calibration every time. I could easily rig up a test with an arduino. you just need to tape a conductive strip to the outside of the container vertically, and submerge a corrosion resistant lead into the water. Gold coated PCB trace would be ideal, and cheap/easily salvageable. You can measure the capacitance which should increase linearly as the water level rises. You can measure it with an arduino using 3 pins, and two resisters, or using a 555 timer, to generate a digital modulated output which could be measured by your drip input on the peachy.

Now there's a new and novel solution I hadn't thought of! Will it be accurate enough tho?

[jsondag]

Now there's a new and novel solution I hadn't thought of! Will it be accurate enough tho?

That's a good question. One that I think more relates to the parts used, and the resolution of said parts, than the method itself. I can test this maybe in the next day or two, just with some foil tape, and my multimeter, and see if that provides decent resolution. for a micro, the test involves charging the capacitor through a known resistance, measuring the time it takes, draining the cap, then repeating. The resistor value, and build of the "Capacitor" will need to be experimented with a bit.

[amoose136]

Capacitance would depend on the dielectric constant which also depends on saltwater concentration so I don't think we've saved much by measuring capacitance instead of resistance.

Laser interferometer with a floating mirror is better but as soon as you add another laser and electronics that can measure time delays that small you significantly increase monetary costs.

[Synchron]

The laser is still there, we could use the peachy laser... But you are right, the sensor elektronics have to be added.

[FredAstaire]

True, but it does seem a reliable measurement can be gotten that way. Possibly by submerging the sensor in the fluid, we could get better results (measuring delta is more important than the absolute level here. We can give it a one-time offset to compensate for the measurement difference too, so the absolute is corrected)

At a previous job I built robots that used the Olympus ultrasonic thickness sensor to detect the thickness of metal plates. It needs a layer of water between the probe and the plate to achieve a good reading. I am not sure about corrosion although most of the probe is anodised metal. The end of the probe is also about the size of a dime.

[jsondag]

Capacitance would depend on the dielectric constant which also depends on saltwater concentration so I don't think we've saved much by measuring capacitance instead of resistance.

Laser interferometer with a floating mirror is better but as soon as you add another laser and electronics that can measure time delays that small you significantly increase monetary costs.

The saltwater is the conductor, not the dielectric. The dielectric is the container wall. It will vary from build to build, but remain constant on a single container.