Water depth measurement

has anyone done any depth of water measurement sensor work/? I want to measure the depth of water in a tank, DIY style not commercial product. I guess these things will be expensive, but are close to what I want Greenhouse clean water tank 15 mWG 4-20mA submersible level sensor (I only really need 2 or 3 m water depth. @Dave Mc, do you have a go-to 4-20mA reading circuit block you always use

Hi Brett, I am interested in this sensor too for a project to monitor a drinking water tank. Need to find out if this is certified for such use. They are not cheap of course but you can find them for around $300 but you need to check if you need something that is certified for potable water (assuming your tank is)

Pressure to water level is easy and their sensor is probably calibrated in meters already. If not, PSI to M is easy as fresh water is a constant density of 1000Kg/m3 and the formula is easy.

Make sure the sensor has a vent tube to null out atmospheric changes or you get errors. Most level sensors are of this type. You one has 2 options. Use the vented one.

Apply +12 to +24V to the +POS wire and connect the SIG wire to you ADC input with a 100 or 200 ohm resistor to ground. Use 0.1% precision type. This will convert the current to a voltage. For 100 ohm this is 0.4 to 2.0 volts and for 200 ohm it is 0.8 to 4.0V

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How much are you guys planning to spend?

You can measure liquid level using a capactive level sensor.

That would be much lower accuracy. I get <1mm depth precision with a 0.25% pressure sensor. For my application to monitor a 20,000 litre tank, I’d like to have a more stable reading.

Could you use an ultrasonic ranger to measure the top of the water? My uncle had this same problem some years ago. He works in water treatment. They ended up using a float on a pulley with a rope. As the float rose the notch on the rope would lower giving them an idea as to how full the tank was :smile:

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Float on a rope is quite often used, you can get them with the top pulley connected to a dial indicator, but you could always attach a rotary encoder.

This looks interesting: https://www.ebay.com.au/p/100m-Wireless-Ultrasonic-Water-Tank-Liquid-Level-Meter-With-Temperature-Sensor-E/10013680005
For under $AU54 you get the sensor, remote display, temperature as well. Shouldn’t be too hard to decode their protocol. I’d grab one for my underground tank, except for the reviewer warning that it needs 500mm headroom. The listing says 0-15 metres, 500mm does seem a lot. I saw a DIY one on Instructables using one of the cheap Arduino ultrasonics I already have that said they only needed a few cm.

You can but they are expensive and they have a blind spot so if your tank has water to the top, you can’t read it.

The float on a pulley works well for sewage as you avoid any blockages and the needed cleaning. You can use a special sensor with the wire to get a signal that a micro can read.

This project (A Water Tank Level Meter with WiFi and More!) in the Feb 2018 edition of “Silicon Chip” may be of interest.

The pressure sensor is available from their online store. Not sure if it is certified for potable water.

haha, you found the reason I was looking… I want to see if there are options beyond their AU$85.50 sensor option, and the answer is looking more like yes plenty of options but not many cheaper… I’m waiting to hear back hat the cost of the one I posted is, but I didn’t ask about potable approved… but I too am looking for potable water as it’s a drinking water tank

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I can’t read the article but I found the sensor and it’s a very good price and also 4-20mA so that would probably work well for your project Brett.

The only thing I can’t find is the accuracy of the output and if this is safe for potable water use.

We tend to use a lot of ultrasonic devices for tank levels. You simply configure the device for depth instead of distance. Dave is right in that there will be a blind spot (blanking distance) where the device is switching from transmit to receive and this is normally around the 300mm mark but on some units might be as low as 150mm.

Personally I would go down the pressure transmitter route in this application. 1 bar = 10m of water so go with a low range unit for accuracy.

Here in the UK you wouldn’t need drinking water approval if it’s for watering plants and there is an air break between supply and maximum water level.

Brett, I found the standard that covers what you can put in the water.

AS/NZS 4020

I’ve emailed Silicon Chip to request a detailed datasheet on the sensor they sell and asked if this is for use in potable water.


My buddy made a level sensor to detect when certain streets in our college town were flooded, as these were prone to constant flooding.

It then would signal a traffic sign down the road so drivers would know not to turn down the flooded street. It was highly effective for a college project imo.

Anyway accuracy on the read was not hugely important, but I think they did get a decent reading in the end.

A vertical tube, a float inside it, and a cheap ultrasonic at the top of the tube pointed down.

yes, that’s probably good enough when you’re thinking about ground water levels. I’ve even thought that a moisture sensor normally open, and closed when in liquid, would do - it’s the basis for pretty much every basement water leak detector on the market, check continuity between two poles a little apart and if there is continuity then you have water. But for wanting to accurately measure and track drinking water levels of tanks that you can’t get easy access to a wired probe seems a good solution, there’s a simple one-off install and reasonably reliable use after that. Adding a tube and float could be quite a hard task on a large concrete tank, but popping a wire in the opening of it is less problematic… but yeah your mate’s project is a pretty good one for the situation faced

Seems to be plenty of potable water sensors out there. It all comes down to price. Certification bumps up the pricing from your basic level sensor for things like rivers etc. I use a lot Exia IS rated sensors for fuel tanks and that adds around $150 to $250 to each sensor then you add the additional cost for the Zener Barrier in the safe area and you start getting expensive. :slight_smile: