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Postby pidar » Wed Aug 09, 2017 11:44 am

Hi
I have been using this to measure soil mositure and after a few weeks this has happened please see photo
Order ID: #194511
Version of Raspberry: Pi B+
Part Code/Part Name :MMP-0124
Fault: Its corroded away
Troubleshooting Completed:
Test soil PH - PH 7 neutral
[img]MMP-0124_for_email.JPG[/img]

Regards
Philip

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Postby Jake » Wed Aug 09, 2017 4:01 pm

Hi,

Oh my, what a corroded spade you have there! These will of course corrode over time, but seems strange that one side has gone in such a short period of time, but the other side hasn't. . .

Happy to issue a replacement?

There's a couple of things you can try to prolong the life.

1. Regular cleaning with a soft implement.
2. If it doesn't affect the reading (or you can adjust for the difference), perhaps try putting some grease or 3 in 1 oil on the prongs, just to give them some extra protection? Worth a test anyway. Hammerite would probably affect the reading too much :lol:

-- Jake

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Postby BMS Doug » Wed Aug 09, 2017 4:28 pm

Wow!

It kind of looks like you've had some electrolysis going on, the anode seems to have dissolved almost completely.

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Postby pidar » Fri Aug 11, 2017 10:27 am

Hi
A replacement would be good.
However this is part of a project to install a network (10) of these in a poly tunnel and taking each one out and cleaning, say every week is not going to make the owners happy.

This corrosion or electrolysis started after a few days, I just thought that is was “surface tarnishing”

And I am not sure that grease or oil is organic! – Maybe organic olive oil then.

If this is electrolysis as suggested by BMS Doug - I never thought of that (thats why Forums can be great).
What about me painting a new sensor with galvanising paint?

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Postby Jake » Fri Aug 11, 2017 2:14 pm

Hi,

Sure thing, I'll get a replacement out to you today!

Yup, sounds like cleaning isn't an option, so coating is probably the way forward.

https://www.bluesea.com/resources/108/E ... _Materials

Zinc looks to be slightly more conductive than nickel (which is what the spades are pre-coated in), so you may need to adjust your sensitivity, but otherwise I don't see why it wouldn't work?

If you get good results, could you post them back here please?

-- Jake

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Postby BMS Doug » Fri Aug 11, 2017 4:30 pm

If it is Electrolysis then using an iron nail as a sacrificial anode would be a possible solution. (I think the nail would need to be electrically connected to the anode to do any good, Your sensor may need re-calibration to account for the nail).

http://www.marineinsight.com/tech/understanding-sacrificial-anodes-on-ships/

The reason I suggest electrolysis is that all of the corrosion has occurred on one prong of the sensor, with nearly no corrosion on the other.

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Postby pidar » Tue Aug 15, 2017 11:03 am

Hi,
I received the replaced yesterday 14/08/17 - quick work thanks and I will paint and test then let know how its goes

Thanks once again

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