Looking for a way to sense water level -- through glass

My home brewing system has this sight glass... A glass tube which shows you the level of the liquid inside the kettle to which it is attached. If pump speed is too high and this water level drops too far, you expose the heating element in the kettle to the air, which is bad.

As some extra insurance should I be distracted, I'd like to find a way to sense this water level with some kind of Zigbee or Zwave gadget.

One catch is that the color of the liquid can vary, from clear to beer-colored.

Another catch is that this cannot be something that takes 30 minutes to install every time I want to use it... Maybe not even 5 minutes. Brew day is long enough and this sensor is supposed to be a net time saver.

My best idea so far is a magnetic contact sensor, with a floating magnet in the tube. However, it may not be possible to find a magnet strong enough to trip the sensor which can also float in that narrow tube. I can also imagine that this would be fiddly to set up each time. Something that clips on to the outside and looks for the meniscus passing by feels like the right idea but I've never seen a sensor like that.

Let me know if you have any ideas!

Can you run wire inside the tube? My first thought would be to secure two wires inside the tube with the ends exposed at the lowest acceptable water level. Then connect the other ends outside the tube to the leads on any leak sensor and set your notifications for any time the leak sensor is dry.

Yes, that might work. The wires would have to be something food-grade though. I might be able to run extremely thin copper or stainless steel rods in there.

It would need testing, it's possible that once the liquid level dropped past the ends of the probes, enough water would be sticking around by surface tension to still complete the circuit. The probes probably could not touch the glass walls for that reason. Not a bad idea though!

I see a couple of ways, I think the best (most reliable) is to have a strong floating magnet, with several small reed switches on the outside. it won't tell you to the inch but with several reed switches you should get enough feedback as to where the level is.

Others would be optical.

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Another option might be to use an optical sensor that only checks as good when obstructed.
The fun part would be finding a sensor that the clear water diffraction would still interrupt.

I was initially thinking of the windshield wiper rain sensor type of optics, where they're using flat glass acute angle refraction that is then disturbed by liquid on the far side. This might work, but is likely overkill for your application.

An optical sensor that could watch for a disruption could work -- I could add an opaque float to the tube. Hmm!

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Maybe LIDAR looking down the tube?

Search for the Capacitive Water Sensor. There are many on Amazon. Here is an example:

The output must be wired to whatever ZWave or Zigbee Contact Sensor.

Neptune systems Apex A3 Jr that comes with an optical sensor that plugs into the FMM port on the A3 Jr.

Where to buy?

And today is the last day of the sale on this product. They don’t go on sale often.

Then use the driver from @snell to get the data into Hubitat.

And setup alarms or actions based on reported data.

The way the optical sensor works is if fluid is touching the sensor the switch state is closed and if fluid is not touching it then the switch state is open. Admittedly you would have to ensure the sensor is cleaned because at times in my aquarium salt mixing barrels where the optical sensor goes dry it does get a salt residue on it from time to time that can cause it to not report correctly but I periodically wipe it off and never had any issues. Just requires a small amount of maintenance from time to time. The sensor would go inside the tank held on by a magnet outside the tank. Sensor is fully encased and will not leak or leech into your brew with the disclaimer that you should always check and verify the sensor to ensure its integrity before use each time.

The optical sensor won’t fit inside the site glass. You’d need to install it inside the kettle.

Now this is an interesting gizmo!

Thanks for the ideas everyone - I am going to investigate this first.

I'm thinking that one of these Linptech Human Presence sensors put right on the glass tube and shielded from other goings-on by some surrounding material (?) and adjusted just right in the driver could easily tell the difference between a full-of-liquid tube and an empty tube. Maybe.

Human Presence Sensor ES1,Smart Motion Sensor with 24G mmWave Radar,Occupancy Sensor Requires Tuya Zigbee Hub for Home Security and Automation,Compatible with Alexa,Smart Life,Z2MQTT,ZHA https://a.co/d/0dNsoqoQ

That's not a bad idea. I was already thinking about getting one of those to play with.

I am using one to keep the bathroom light on by sensing motion in a glass-enclosed shower. Works very well. Similar task on a larger scale.

Good luck. Very unlikely this will work.

You could ignore the sight glass and look at the current through the heater element. If the element isn't in a water jacket it will over heat and the current will drop as the resistance increases. Current is very easy to measure. Just switch off the element at an abnormal current excursion and then sound an alarm.

If that won't work put a small float in the sight glass with a magnet on it. Then put a couple of magnetic sensors outside the glass. You can track if water is rising or lowering by which switch closes first. Take a look at a Kuerig coffee maker, they use such a scheme to test if the water reservoir is empty.

How can easily I measure current on a 240V circuit in a way that is easily observable by Hubitat? (Also, this is not a project that merits a couple hundred bucks... Maybe fifty bucks.)

Also, killing power to the CPU would kill the heating element, but it would also terminate the recipe in progress and mess up the timers. I would want to terminate current to only the 240V element which sounds like a lot of extra parts.

A simple warning a few minutes before the element went dry, catching the water level crossing a single point, would be preferable.

I received the gizmo that @vitaliy_kh suggested, and while it's very cool, it unfortunately cannot detect liquid in the sight glass. It can see through a plastic pitcher, but as soon as you get it near the glass and aluminum sight glass, it just shows liquid present regardless of there being liquid there or not. If there's any way to tune it, the instructions don't mention it.


The technology itself is OK if sensor is designed for the water/liquid detection purpose. The Linptech Presence sensor is a very different story...