Underwater temperature monitoring device

Projects General Guidance
1

Good day everyone.
I'm here to ask about any suggestions, ideas and professional guidance regarding my project about vertical temperature stratification using arduino in a lake.

My problem is, I dont have ideas on what is the best sensor that I can use to determine the temperature under water, with different depth, that will last for about 3 to 5 months data logging.

Can anyone could suggest to me what sensor should i use?

Thank you

2

Interesting questions, lots of possibilities. We need to narrow this down.

  1. What is the maximum probe temperature worse case?
  2. What is the minimum probe temperature worse case?
  3. What accuracy do you need?
  4. What is the ambient temperature range?
  5. What is the ambient humidity range?
  6. How much drift is allowed over time?
  7. How long will the sensor cables be?
  8. What is your power source?
  9. What are its limits?
  10. Do you have a reasonable budget?
  11. How many samples per day?
  12. How many samples will you have to store?
  13. What is the sample data configuration (byte, word, string, ..etc)?
  14. How is it going to be packaged?
  15. If a primary or rechargeable power source what is the life required?
    This is a start, what else do you know that will help us?
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3

First consideration : DS18B20
There is an encapsulated version, which is the obvious one to buy, but it is waterproof only up to a point. You will need to get liberal with epoxy or something.

The advantage of the DS18B20 is that you can put many sensors on one Arduino pin.

If you can get them similarly packaged, you may find thermistors are entirely adequate.

The depth of the lake may have some bearing on your choice.

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4

There is an entire set of web pages devoted to DIY underwater data logging with Arduino: About Us | Underwater Arduino Data Loggers

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5

Thank you! Your questions give me insigns in different aspects of prototyping the device. This is the answer to you questions.

  1. What is the maximum probe temperature worse case? Approx. 35°C
  2. What is the minimum probe temperature worse case? Approx. 15°C
  3. What accuracy do you need? Atleast 80% accuracy
  4. What is the ambient temperature range? 30°C to 40°C
  5. What is the ambient humidity range? 60-80
  6. How much drift is allowed over time?
  7. long will the sensor cables be? 5m or 10m if possible
  8. What is your power source? a DC power source, depends on the sensor power source needed
  9. What are its limits? No answers for this yet
  10. Do you have a reasonable budget? Yes.
  11. How many samples per day? 48 data per day
  12. How many samples will you have to store? 4000+ samples
  13. What is the sample data configuration (byte, word, string, ..etc)? No planned yet, but i can consider wireless data logging
  14. How is it going to be packaged? Still in planning stage for possible prototyping and interfacing of a sensor to arduino
  15. If a primary or rechargeable power source what is the life required? 3-5months
6

Thank you! This helps so much for me to be able to consider different type of sensor. I look at read about this sensor

7
  1. This does not appear to be reasonable to me. 20C that is about 1.6 degrees C (+-0.8). I would expect the gradients to be in the 0.01 degree range but I know very little about what you are measuring.
  2. This will be in a building?
  3. That is ~5K byte. FRAM may be your best bet as it is low power, non volatile, and fast.
    Later,
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8

Use a single or series of thermowells with DS18B20’s .
I use two in my fish pond , been in about 5 yrs now. Calibrate them alltogether first

.

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9

Can you send some picture of it or link to where i can buy ? I struggles in finding it on web

10

Amazon eBay.. These things can't possibly be hard to find. Note that they come in different cable lengths, up to 5m, which may be useful.

Screenshot_20230929_132503_com.android.chrome
Screenshot_20230929_132503_com.android.chrome1080×2280 182 KB

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11

beware
Those you found maybe ( they look good ) but many sold as waterproof are not , despite what it says , the tip is , but you cannot submerge the cable - a few you can , but many from Amazon etc you cannot .
Pressure rises rapidly and they may not work at depth ??

Here

You can make a thermowell from a length of copper tube , seal the end with a solder fitting and fit your sensors daisy chain and lower them inside the tube .You can back fill with a silicon oil if you wish .
Or ( better still ) make up for a single sensor with a capped short length of copper tube joined to a plastic length ( use plumbing fittings for this ) .
Submerge !!

Read me !

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12

If OP never worked with DS18B20 before, each one come with a unique serial nr. Connect one at a time, take note of the s/n and label the sensor so you know the correlation. Otherwise you'll end up with a bunch of sensors and not knowing at which depth each and one are at.

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13

Supplemental question.
If your mounting arrangement were a single vertical 'stick' to be lowered into the water, how many sensors would be mounted on the stick, and what is the range of positions? Your answer might be something like:
21 sensors, 0.5m spacing, 0 - 10m range.

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14

Yeah exactly

15

I'll consider it. Thanks for this.

16

People seem to imagine this as something to be lowered into water. I would go the opposite way and build all into a sealed, water proof box and anchor to the bottom. The temperature sensors would be floated in line to the surface. I would have a multi-conductor cable to the shore that provides power and receives data from the box on the bottom of the lake.

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17

Usually the fewer joints you need under water the better

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18

Correct, of course! But if the OP is looking for an autonomous monitoring device, he had better be prepared to build several so at least one will work for the required time. By having a shore connection the underwater device can be monitored real-time.

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19

Hello, I would like to ask if where could I find thermowells that can fit on DS18B20?

20

I either never found a thermowell, or never found a thermowell I was prepared to pay for, so I made my own. I'm not sure a thermowell in the accepted sense is what you need anyway. A thermowell is inserted into a wet tank or pipe, and the sensor is kept dry on the outside. In your case I think you intend the sensor dry inside a pipe which is wet on the outside - something totally different. I imagine you need no more than a short length of pipe for each sensor with a compression gland at each end. It would also act as a sinker.

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