Clyde Smith-Stubbs wrote:
>
> I need some suggestions on a couple of sensors;
>
> 1) I need to measure water level (and thus contents) in a concrete tank.
> The tank is about 2m deep, so a float is probably not practical. My
> thoughts are either an ultrasonic setup to detect the water surface,
> or a pressure sensor. The ultrasonic setup will be complicated, the pressure
> sensor would either have to be at the bottom of the tank, or above it with
> a hose to the bottom. The hose idea would rely critically on having no air
 leaks
> in the hose, difficult to guarantee for a long time. Submerging the pressure
> sensor would leave it liable to getting blocked by stuff on the bottom of the
>  tank.
>
> 2) I need a "light beam" sensor to detect vehicles or people moving down
> a driveway - much like a door minder used in shops, but to operate outdoors
> spanning a distance of about 20m. It should preferably use infra-red so as not
> to be visible (this is not critical, but if it uses visible light it should
 not
> be too bright). The electronics side of this is reasonably straightforward -
 I'd
> modulate the beam at some frequency, recover the modulation and differentiate
 it
> to detect sudden interruptions. This should make it immune to external
 lighting,
> fog etc. The hard part is what kind of light source, detector and lenses to
 use,
> especially for infrared.
>
> All suggestions from this esteemed collection of minds will be gratefully
>  received.
>
> Clyde

To 1)
Have a look at the Magazin ELRAD (from Germany), 2/98 and 3/98, they've
got a
project doing exactly what you want (measuring the waterlevel in a tank
using ultrasonic and controlling various pumps and so on)
Hope I could help a bit,

greetings ,
             Reelf

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