How would you test a moisture meter?

Note - I wonder if we should have a series of “How would you test ABC” in which ABC is a simple product which many people would buy. People want to test the product properly before the return window to be sure that they are getting a quality product. You as a tester can help them. How does this idea sound ?

The problem:
I would like to buy a moisture meter for my plants so that I know when to water them. Without a meter, I have to dip my fingers into the soil regularly & wash them with soap which is too much work. There are too many meters on the market and I am not sure if they really work. I would like to run some tests to see if they work or not and if they have any flaws. The max time allowed to test it is the 30 day return window. Please suggest ways to test a moisture meter.

Product link - https://www.amazon.com/Alotpower-Moisture-Hygrometer-Outdoor-Battery/dp/B06XC6QD3B

Product photo:

Product specifications: (copied from the product link)

  • Moisture Meter for Plants:Make your plants more healthy by Soil Moisture Sensor Meter.
  • Easy to Use: just need plug and read.
  • No Battery Required:Simply push the meter into the soil, and you’ll get your reading. It’s no need for batteries.
  • Both for Indoor & Outdoor Use:Easily know when to water for your flowers, plants.
  • Scientifically Accurate:Easy & accurately to read moisture promotes healthy plants.

Points to consider:

  • Meter sellers ask you to not dip the meter into water. Its not meant to detect water, but only moisture in a medium like soil. So, maybe avoid that negative test? Is that an invalid test or are the sellers trying to fool you?

  • Ask the user how they will use the meter. Are my plants potted (yes) or in open soil? Are my pots next to a source of mist/steam by any chance? Am I going to consecutively dip it in pots with different amounts of water? Could that impact the readings? What if the probe bends because the soil is hard and dry? The product is cheap & just $15 or so but the risk of over watering is rotting plants. It is not always possible to recover from that.

  • Should we break open the product and inspect its contents? How does it really work?

PS - I understand that this might seem like a trivial problem, but we might actually need to do some difficult science to test this properly. But, deep testing is not my goal. My goal is to run some basic smoke tests with your help to make a decision whether to keep or return this product. Of course, there is no liability for your suggestions :slight_smile:.

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My problem, is that as someone studied in electrical engineering I would go down that route probably and be testing the meter mechanically.

  • Mechanical testing may be a good thing from a durability viewpoint, but also a bad thing from lack of focus viewpoint.
  • I would also want to verify that it does not classify as a dangerous weapon …
  • Verify chemical contamination of the probe does not impact accuracy by using in a weak alkaline and acid soil for long periods to determine if chemical action degrades the instrument.
  • Verify that it operates at the depth desired by gardeners (indoor pots or outdoor in deeper beds)

I assume the don’t immerse probe in water is logical because that’s likely to let water into the probe - and will “bin” any test results and the device. Oooooh anyone for “destructive testing”? This coudl get good.

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Yes please :slight_smile:

Hi @raghu. Interesting and practical task/challenge, thanks. I think ‘seeing’ how a tester mindset works would be very interesting for folks considering getting into the field, so I would support your idea of having a series of these tasks. It would also be helpful for folks in the field for some time to consider other possibilities/approaches/thinking by seeing how others approach it.

Disclosure:
I have one of these devices and it has helped me a lot in watering my plants, so this may skew my results/approach, but hopefully the below may have value nevertheless.

Fundamental approach/interpretation of the task/challenge:
Take a practical approach to testing the device (unfortunately this means no destructive testing :frowning:) over the course of 30 days.
As we’re talking Amazon as a supplier, I know they have the returns policy so I am going to assume I can get several other devices as a basis for comparison, i.e. not being an electronics expert, i am going to attempt to validate the product specification claim “scientifically accurate” through practical observations (i.e. looking at plants) as well as more (proto)scientific (i.e. comparing three different meter’s results)

Questions I would set out to answer in testing/approach I would take:
Purchase (with zero intention to keep, i.e. I would get refunds for the high and mid priced) three soil meters of varying price, obviously the one for our testing which we may keep, and two others, one at the top end of price, the other middle of range

Test setup:

  • Determine which soil(s) I need the meter to work in
  • Determine which environment(s) I need the meter to work in
  • For both the above, identify soil/environment which has plant(s) representative of what plant(s) I need the meter to work for
  • Determine the initial health of each plant (not sure how to specifically do this, but thinking of marks out of 10 just to keep it basic/simple/practical)
  • Determine what we mean by the terms ‘easy to use’ and ‘robust’. I would ask a user for their input into this and when I am performing the testing each day make my own observations which I would factor in the final test report as well

Test execution:

  • For 28 days, each day at 9am and 9pm using each of the 3 meters, measure the moisture and assess plant health for each plant/soil/environment and record. Water plant only if the meter we are thinking of buying indicates it needs it (i.e. water in accordance with its instructions, which are hopefully very clear, if not probably reject the meter on that basis alone!)
  • Make any observations on ‘easy to use’ and ‘robustness’

NOTE: the above was done over 28 days + 1 day prep meaning we have one day to do the below and send back the meters

Test analysis:
Generate metrics to show how reliable the meter was versus the other two we are sending back
Generate metrics to on plant health

Test outcome:
Generate report showing convergence/divergence of readings and plant health versus the original readings and draw your conclusions and recommendations. Also factor in any observations on meter robustness (i.e. was it ‘easy to use’ and ‘robust’)

Assumptions:

  • Dipping the meter into water is a claim that SEEMS reasonable when we read the information in several of the devices (assuming they operate similarly), but also searching on internet about the mechanism of operation which is that the meter measures the electroconducivity of whatever it is inserted in, and water has a LOT of electroconductivity versus soil with much less moisture. So it seems valid to assume the meter would not take kindly to being immersed in water. Therefore, to me I would avoid any such testing.
  • Breaking the product open and assessing contents is not within my skillset so i would not do this. The other point about this is it may invalidate the possibility of sending it back to Amazon so I would not do this
  • I am assuming we have lots of soils environments and plants available as I am assuming this is a very practical testing, ie. not a lab setup. However, I think the principles are the same for each, except in the lab you would likely look for more variety
  • I am assuming that soil SO hard it would bend the meter is not in scope and/or this is not a valid test type as I am imagining my own garden setup as like an average one, which may or may not be valid as I live in Ireland where it rains a lot so my outside soil is pretty moist and soft which may not be the case in other parts of the world. My indoor pots are all soft enough to not cause a meter problems (at least that is my assumption based on my experience of them)

As I said, this was an interesting exercise and I would like to see more of these if others find them helpful :slight_smile:

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