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current reading for soil moisture meter

Hi. I recently made a small mistake. I purchased one of those probe type "Made in China" soil moisture testers. There was a gardening workshop, and the UC Master Gardeners group recommended the use of these meters to prevent over or under watering.

The meter had no reading, even in soaking wet soil. It also had no reading in dry soil. The resistance, as measured by a DMM , across the probe tip was infinite. The meter was opened and the probe disconnected. The measurement of resistance across the D'Arsonval movement meter was similarly infinite. There were solder blobs and solder spray across the front of the meter, indicating a sloppy assembly technique. Since the case was now damaged, and the package was long since discarded, this meter could not be returned. It is likely that the probably now moved-on Chinese manufacturer would not accept it back anyway.

Since the probe part looked like a battery (dissimilar metals), a current reading was taken on the aformentioned dry and saturated soils. A reading of 6 microamps and 700 microamps were obtained, respectively.

Does anyone know the calibrations of the meter, offhand? Are these rmeasured values representative of the observed range?

If a decent range can be provided, the meter (without the movement) may be salvageable.

Thanks, Eric

Reply to
ericchang
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Made in rip-off land ;) Read about the "Dell" transformer with extra metal weight for that robust feeling. And missing ground, thermal protection etc.. ;) Or the wlan adapter where the antenna is just a piece of plastic. Or the FET's that don't manage even 1/4 of their rateing..

You could tell the shop you want you money back. And you can prove that the product was faulty.

You can use "buffers", it's liquids with precise pH value. And the buffer will not change pH unless you push them far with acid or alkaline. Blood infact works in a similar way to keep pH balance. It might even work to use that substance too. It's readily available, and got a documented pH :)

Reply to
pbdelete

What do you suggest should be the soil moisture calibration setting, assuming the soil is saturated with the OP's blood?

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

"too wet?"

;-)

Reply to
Rich Grise

On Mon, 12 Jun 2006 09:50:21 -0700, ericchang wrote: [about dead plant soil moisture meter]

Apparently so, yes. :-)

Sure - calibrate it! Set up a small array of pots, and let one get bone dry, and soak the dirt a different amount in each, until the one on the other end is "too wet"; then use an ordinary microammeter and note the current for each saturation level - then the one that feels "just right" should be mid-scale. :-)

I've also found that by just feeling the soil with your finger you can usually tell if it's too dry or too wet.

Good Luck! Rich

Reply to
Rich Grise

You proberbly only need a drop or two between plates, if you don't ought to get to the pharmacy store. No murder needed :-)

Reply to
pbdelete

I think the suggestion was that the soil be saturated with the manufacturer's blood. Ed

Reply to
ehsjr

I have always assumed that these cheap pos soil wetness indicators are just 0 to Fs - in your case 0-1mA - movements with limiting so the battery doesn't fry the meter. Ed

Reply to
ehsjr

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