I have been posting few updates in this forum where I listed the options I was considering for water level measurement in my rainwater tank. I somehow strongly accentuated the ultrasonic method of measuring but never actually implemented it as the price of these sensors kept this item low on the priority list. Until I found this – The pressure based water level sensor. Some time ago I noticed these products already, but the ones I was looking at were not suitable for Loxone, these were with current output (instead of voltage), which would require additional HW converting it, not talking about space requirements in the cabinet, and so on. But now this is different.
Let’s have a look at the level sensor I purchased. It has robust stainless steel body, it can be powered by 9-36VDC and the output is 0-10V! Damn! Why haven’t I found this earlier 🙂 The sensor is great, but we will get there.
If you plan to order one of these, make sure you select the 0-10V variant and also provide additional details about cable length and measuring range. I am not sure about the detail how this can get customized, I was offered to choose the measuring range and cable length in whole meters, not a fraction (like 0-2 meters range, 3m cable). For my tank, the measured maximum depth is 108 cm (after that it starts overflow, event though there is a some additional space), so I was fine to order measuring range 0-1 meter, and 2 meters long cable.
I think I do not need to explain, how these sensors work, right? Unlike the ultrasonic ones which are mounted above the water and measure the time (and thus the distance) getting the echo from the reflection of the ultrasonic signal, the pressure based level sensors are mounted at the very bottom of the tank measuring the water pressure difference against the atmospheric pressure. Now, how can they know the reference atmospheric pressure that follows weather changes? The trick is in the cable which has a small ventilation hose that brings the external atmospheric pressure into the sensor. That’s why you need to specify the cable length before purchase and the connection point must be above the water level.
The biggest problem I had was unexpectedly the connection itself, where I wanted to use RJ-45 socket, but apparently I was unable to make the right connection in the connector. I temporarily solved this issue using fixed connection in the installation box, but for the future I want to have the sensor removable. I just need to find the right and robust connector for this purpose. Apart from that the installation is trivial, just three wire connection (24V+, GND, 0-10V output). A recommendation from my side again would be to fuse all external devices to prevent total system shutdown in case of any short-circuit failure on the 24V wires. Especially in the environment like this, which is extremely humid with sensor located permanently in the water, it is a good practice.
The wiring diagram I received was in Chinese, but there was nothing about the wiring colors for this type of sensor. However the seller responded pretty quickly, and confirmed the following wiring details.
I have the sensor installed for about a month now and my biggest surprise is the accuracy of the measurement. This is totally beyond my expectations! The output from the pressure sensor is stable, without any wobbles in some range or something, and it registers every millimeter change in the water level height. Stunning results!
In my case the measuring range 0-1 meter, which means 0V on the output for empty and 10V on full (1 meter high water level) tank. Knowing the shape of the tank, I can also visualize the remaining tank water in liters. In the statistics then I can see not only the remaining amount, but also how much was consumed or added and when.
I have created an icon that illustrates the amount of water in the tank. This way it can be visualized on the dashboard. There are six levels I display using this icon, precise details are obviously in the chart.
Here are the assigned values:
The sensor is giving me exactly what I needed, and the precision is higher than I would have expected.
On the roadmap
Few interesting outcomes can be generated using this. Firstly, while having the rain sensor installed, I could report the rainfall intensity, water consumed vs. stored. It is almost similar to what the energy meter block offers for solar panels, just applied to water. And lastly, better management of garden irrigation is something I will be working on.
I cannot fully compare the ultrasonic sensors with the pressure ones. Both will have its own domain where one or the other will dominate for particular reason. The advantage of the pressure type of measurement is the ability to measure in narrow spaces, where ultrasonic sensors would suffer from unwanted reflections. These can be created by several obstacles in the way (spider’s net, floating water) resulting in false alerts.
On the other hand, pressure sensors are laying at the very bottom of the tank all the time. They are impacted by the liquids they are in, and can degrade over time. I am really curious how long these last before something bad happens.
To sum this up, the price of this pressure water sensor was 50 USD incl. shipment. It is roughly one fifth of the price for the industrial reflective ultrasonic sensors I listed earlier.
Update March 3rd 2019: After about a six months of operation the water level sensor status started appear as “disconnected”. Quick inspection revealed that the problem is in the cable connection located on a top of the tank area. I fully admit that the use of RJ-45 connector was a really bad choice for such humid environment. The contact pins were covered with massive corrosion.
I rebuilt the connection box using the massive 3-pin XLR connector from Neutrik. We’ll see how long it will last.