What's inside a dishwasher turbidity sensor?

[e100]

For example, http://imgs.inkfrog.com/pix/usedapplianceparts/635_KITCHENAID_WHIRLPOOL_KENMORE_Dishwasher__W10134058.JPG
I'm interested because these things are way cheaper than lab grade sensors. The application I had in mind is detecting algal blooms in water.
I haven't found any pictures that show the internal circuit board of this particular sensor type. It looks like there are 3 optical elements but I've also seen simpler (perhaps older) designs that just look like a larger version of a slot photo interrupter.
Do the newer designs measure the amount of side scattering similar to the way lab grade sensors work?

Mike

[Signal32]

See below for what the one you linked looks like inside.
I'm not sure how it works, probably not much different than the older one. Best guess is that it works the same but with an added sensor to measure scattered light.
The older one seems to be only a LED + Photodiode.
The price difference could be that this does not include any controller/logic, all of it being built into the dishwasher.

[e100]

In the last image, is the black blob a light stop, or is it directing the unscattered light down to the endmost sensor?

[mikeselectricstuff]

The black looks like the normal IR-pass filtering plastic package of a photodiode

[e100]

The black photodiode glued into the housing?
Perhaps the PCB in the top picture had to be ripped out leaving the photodiode behind?

So perhaps a in-line photo-interrupter to sense large bits of food debris and a receiver(s) at 90 degrees for the smaller particles scattering light?
Does that sound reasonable?