On Mon, Oct 10, 2011 at 11:40 AM, Brent Brown <brent.brown@clear.net.nz> wr=
ote:
> I came across these sensors a few years ago while working on a project to
> automatically sort cattle through automatic gates. These proved excellent=
 for
> sensing black cows (very low infrared reflectivity)... for example other =
opto sensors
> we trialled would give a number of output pulses as a Friesian/Holstein c=
ow (black
> and white patches) walked past!
>
> http://sunxsensors.com/index.php?main_page=3Dindex&cPath=3D40_146
>
> They have several noteworthy characteristics as far as Infrared diffuse r=
eflective
> photoelectric sensors go:
> 1) Not affected by object colour or background
> 2) Adjustable distance (ignores objects beyond set distance), mechanical =
adjuster
> not electrical
> 3) Large operating range (at least 2m)
>
> I would like to know how they work, instruction manual gives some clues. =
From
> page 2 of manual, "Principle of fixed-focus sensing with 2-segment photod=
iode"
> "Normal reflective type sensors operate by sensing the variation in the a=
mount of
> incident beam. However, the fixed-focus reflective sensing type sensor
> incorporating the 2-segment photodiode operates by sensing the variation =
in the
> incident beam angle. Thus, the output is activated according to the dista=
nce of the
> object from the sensor. This system helps the EQ-30 series in being unaff=
ected by
> object color or a background, enabling stable sensing."
>
> I can perhaps visualise how 2 sensors help differentiate between near and=
 far
> objects. A lens (or even a pinhole?) might allow the incident beam angle =
to hit one
> or both sensors depending on distance to object... I could be wrong and/o=
r there
> might be more to it than that. How would that help with object colour per=
formance?

The SUNX terminology is a bit confusing, usually "fixed-focus" (sometimes c=
alled
"background blanking") is a cheap form of "true" Background Suppression usi=
ng
light triangulation. Usually they use only one photodiode and the sensing r=
ange
is usually only good around the focus range. Probably the SUNX sensor is
the true BGS type and use light triangulation. It will belong to the type
of

Mechanical  background suppression" is usually more expensive and better th=
an
"electronic background suppression".

Ref:
http://www.sensorsmag.com/sensors-mag/the-rise-diffuse-mode-photoelectric-s=
ensors-1506
http://www.pepperl-fuchs.com/global/en/15514.htm
http://www.baumerelectric.com/usa/news/Minos/MINOS_BGS_essay.html

> I'm researching sensors for another application, which requires 1 and 2 a=
bove but
> not necessarily 3 (0.5m range would be ok). The SunX sensor would do it, =
but way
> too expensive (USD148).
>

You may want to check if they have visible red light version which
will have lower
sensing distance. SUNX sensors are usually cheaper than companies like
SICK, Omron and Pepperl+Fuchs but it all depends on the source you get.
You might want to search the offerings from these vendors and other
vendors (in US, there is Banner Engineering).

This one is the latest from Pepperl+Fuchs and I do not know the price.
http://www.pepperl-fuchs.com/global/en/15171.htm

I was the lead designer (project lead, HW and FW designer) for the
Series 31 (RL31/RLK31) photoelectric sensor released back in 2006
when I was working for Pepperl+Fuchs Singapore, but the above one is
a later addition to the series.

--=20
Xiaofan
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