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'[EE] Infrared proximity sensors'
2011\10\09@234120 by Brent Brown

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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 cow (black and white patches) walked past!

http://sunxsensors.com/index.php?main_page=index&cPath=40_146

They have several noteworthy characteristics as far as Infrared diffuse reflective 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 photodiode" "Normal reflective type sensors operate by sensing the variation in the amount 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 distance of the object from the sensor. This system helps the EQ-30 series in being unaffected 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/or there might be more to it than that. How would that help with object colour performance?

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

Thanks, Brent.
-- Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  spam_OUTbrent.brownTakeThisOuTspamclear.net.nz

2011\10\10@013446 by Xiaofan Chen

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On Mon, Oct 10, 2011 at 11:40 AM, Brent Brown <.....brent.brownKILLspamspam@spam@clear.net.nz> wrote:
{Quote hidden}

The SUNX terminology is a bit confusing, usually "fixed-focus" (sometimes called
"background blanking") is a cheap form of "true" Background Suppression using
light triangulation. Usually they use only one photodiode and the sensing range
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 than
"electronic background suppression".

Ref:
www.sensorsmag.com/sensors-mag/the-rise-diffuse-mode-photoelectric-sensors-1506
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 above 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.

-- Xiaofa

2011\10\10@130626 by Michael Rigby-Jones

flavicon
face


> -----Original Message-----
> From: piclist-bouncesspamKILLspammit.edu [.....piclist-bouncesKILLspamspam.....mit.edu] On
Behalf
> Of Brent Brown
> Sent: 10 October 2011 04:40
> To: Microcontroller discussion list - Public.
> Subject: [EE] Infrared proximity sensors
>
> 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
> cow (black
> and white patches) walked past!
>
> sunxsensors.com/index.php?main_page=index&cPath=40_146
>
> They have several noteworthy characteristics as far as Infrared
diffuse
> reflective
> 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
> photodiode"
> "Normal reflective type sensors operate by sensing the variation in
the
> amount 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
> distance of the
> object from the sensor. This system helps the EQ-30 series in being
> unaffected 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/or
> there
> might be more to it than that. How would that help with object colour
> performance?

The Instruction manual PDF on then page you linked to has a very
simplified explanation.  AFAICT: ambient light, or a target outside the
operating range would cause both photodiodes to receive a similar amount
of light, but a target within the focal range will cause one detector to
receive more light than the other. By setting a threshold against the
ratio of the two photodiode currents rather than the absolute value,
variation in the total amount of light falling on the detectors will be
ignored (within the dynamic range of the sensors!), but it becomes
sensitive to the distance to the target.


Cheers

Mike

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2011\10\11@051151 by Brent Brown

picon face
{Quote hidden}

Many thanks! Good info in those links, just the explanation I needed for how Background Suppression works.

Yes, I think the SUNX sensor is "true" Background Suppression from observing the way it behaves... it has a very precise cut-off point (adjustable operating distance) that does not seem to vary with objects of different reflectivity. Perhaps it technically does have fixed focus optics, and the mechanical adjuster shifts the position of the photodiodes? I'll ask about a visible red version, though they don't list one on their website.  
Now I'm also wondering about Foreground Suppression, but at least I now know a bit more terminology which will help in my searching.  
I imagine it would have been very interesting to work on the RL31/RLK31
sensor project, and rewarding to see your "babies" graduate into the real world :-)
-- Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  EraseMEbrent.brownspam_OUTspamTakeThisOuTclear.net.nz

2011\10\11@052516 by Brent Brown

picon face
> The Instruction manual PDF on then page you linked to has a very
> simplified explanation.  AFAICT: ambient light, or a target outside the
> operating range would cause both photodiodes to receive a similar amount
> of light, but a target within the focal range will cause one detector to
> receive more light than the other. By setting a threshold against the
> ratio of the two photodiode currents rather than the absolute value,
> variation in the total amount of light falling on the detectors will be
> ignored (within the dynamic range of the sensors!), but it becomes
> sensitive to the distance to the target.
>
>
> Cheers
>
> Mike

Thanks Mike. Yes, from the links in Xiaofans reply that's pretty much how they describe the operation... Let's say the two photodiodes are called R1 which is illuminated by near objects, and R2 which is illuminated by far objects (beyond the focal plane and considered "background"), then the condition for deciding that an object is within range is R1 > R2.
-- Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  brent.brownspamspam_OUTclear.net.nz

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