Thanks Colin, but that=B4s not the case. The probe I said=
=20
is actually a complete digital pressure transducer, with a pressure=20
sensor, ADC, a PIC16F1708, EEPROM memory, etc. It measures the water=20
pressure and sends the digital value in RS-485 to a logger outside the well=
..
                 I just looking for someone that may had experienced the=20
same problem with surges induced in long communication cables, and how=20
they did to fix it.

                     Best wishes,

                                     Dagmar


On 21/09/2015 21:10, cdb wrote:
> n Mon, 21 Sep 2015 10:12:44 -0300, Dagmar Carnier Neto wrote:
> :: Hello all,
> ::                 I'm developing a digital water-level probe to be
> :: installed inside wells, and last week found some of them stop
> :: working.
> :: They were installed inside deep wells, around 250 meters deep. A 4-
> :: wire cable connect them to the top, being 2-wires for power (5V and GN=
D)
>
> If you are providing your probes with DC they will eventually corrode due
> to electrolysis.
>
> You need to provide them with an AC voltage, a simple square wave will
> work, either using a 555 timer or a set of NAND gates set up as an RC
> oscillator.
>
> I have no answer to your pump dying problem, apart from maybe the cable
> goes high resistance or corrodes due to impurities in the water.
>
> I'm attaching a circuit separately.
>
> Colin
> --
> cdb, colin@btech-online.co.uk on 22/09/2015
>  =20
> Web presence: www.btech-online.co.uk
>  =20
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>  =20
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> This email is to be considered private if addressed to a named  individua=
l
> or Personnel Department, and public if addressed to a blog,  forum or new=
s
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>  =20


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