AC excitation of a sensor
Archiver
Posts: 46,084
Dear Stamp List
I have a problem with a sensor (a Watermark gypsum block sensor used for
monitroing soil water) which requires excitation with AC to avoid
polarisation. After excitation the sensor is read by measuring a DC voltage
drop. Anyway, is there any way apply this AC excitation to the sensor with a
BS2 and a direct current power supply i.e a battery pack. I'm not too
familiar with electronics and was wondering if there is an easy (cheap would
be good too) way around this such as chip, or standard circuit which I can
add which will do this easily ? Your advice, tips, remarks,
feasibility/possibility of finding a solution would be greatly appreciated.
Cheers John
_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
I have a problem with a sensor (a Watermark gypsum block sensor used for
monitroing soil water) which requires excitation with AC to avoid
polarisation. After excitation the sensor is read by measuring a DC voltage
drop. Anyway, is there any way apply this AC excitation to the sensor with a
BS2 and a direct current power supply i.e a battery pack. I'm not too
familiar with electronics and was wondering if there is an easy (cheap would
be good too) way around this such as chip, or standard circuit which I can
add which will do this easily ? Your advice, tips, remarks,
feasibility/possibility of finding a solution would be greatly appreciated.
Cheers John
_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
Comments
2 Stamps pins , HIGH - LOW, then reversing to LOW - HIGH inside a loop.
Like this:
loop:
high X
low X
pause n
low X
high Y
pause n
goto loop:
This may emulate a square wave (50-50%) with about 10 V amplitude peak
to peak .
ACJacques
Irrigation Man wrote:
>
> Dear Stamp List
>
> I have a problem with a sensor (a Watermark gypsum block sensor used for
> monitroing soil water) which requires excitation with AC to avoid
> polarisation. After excitation the sensor is read by measuring a DC voltage
> drop. Anyway, is there any way apply this AC excitation to the sensor with a
> BS2 and a direct current power supply i.e a battery pack. I'm not too
> familiar with electronics and was wondering if there is an easy (cheap would
> be good too) way around this such as chip, or standard circuit which I can
> add which will do this easily ? Your advice, tips, remarks,
> feasibility/possibility of finding a solution would be greatly appreciated.
>
> Cheers John
> _________________________________________________________________________
> Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
>I have a problem with a sensor (a Watermark gypsum block sensor used for
>monitroing soil water) which requires excitation with AC to avoid
>polarisation. After excitation the sensor is read by measuring a DC voltage
>drop. Anyway, is there any way apply this AC excitation to the sensor with a
>BS2 and a direct current power supply i.e a battery pack. I'm not too
>familiar with electronics and was wondering if there is an easy (cheap would
>be good too) way around this such as chip, or standard circuit which I can
>add which will do this easily ? Your advice, tips, remarks,
>feasibility/possibility of finding a solution would be greatly appreciated.
>
>Cheers John
Hi John,
http://www.emesys.com/EarthM/em5.pdf
This uses a CMOS 555 timer IC to measure conductivity of water
between two electrodes, which is basically what the watermark sensor
does. The resistor/sensor determines the frequency of the
oscillator, which is read by the BS2 using the COUNT command. The
current is balanced in each direction (AC excitation) Caveat: for
soil moisture it is important to protect the circuit from ESD. More
circuit info at:
http://www.emesys.com/LWET_DAT.htm
-- Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com