I've read that elevator doors operate according to the photoelectric
effect--the electric eye opens the doors if something interrupts its
light beam.

I'm writing a story in which a character uses his knowledge of this
effect to rig an elevator to open on certain floors and remain shut on
others.  I'm looking for some practical elevator science--and maybe a
link or two detailing MacGyver-like scenarios--to justify that plot
point.

So, basically: What's the connection between the photoelectric effect
and the operation of an elevator?  If the occupant of an elevator knew
of this connection, how could he apply that knowledge to affect an
elevator's route?

---

Request for Question Clarification by journalist-ga on 08 Aug 2003 12:08 PDT

Greetings Pempek:

Would you looks at the page at
http://www.simplexgrinnell.com/news_events/ia/fire/03c1g.jsp and let
me know if this is the type of information you are seeking?  It will
help me determine where to focus.

Best regards,
journalist-ga


SEARCH STRATEGY:

"photoelectric detector" technology research
"photoelectric detector" elevator problem
"photoelectric sensor" technology research
"photoelectric sensor" elevator problem

---

Clarification of Question by pempek-ga on 08 Aug 2003 13:10 PDT

Journalist,

The article on that page mentions the photoelectric effect, but only
in passing, and within the context of the history of fire detection,
which doesn't really help me.

I guess I'm looking for two things:      

First, how exactly is the photoelectric effect applied in elevator
technology?  In my basic searches I've found a few sites that state
briefly that "Einstein's theories made elevators and automatic doors
at supermarkets possible," but none that really lay it out: "Here's
how the photoelectric effect works, as illustrated by the electric eye
in a common elevator."

Second, are there any stories, anecdotal or hypothetical, of people
re-routing an elevator car by adjusting the electric eye?  The
absolute ideal, and I'm doubtful I'll find this exact thing, would be
step-by-step instructions--like those Worst-Case Scenario books that
enumerate the steps to fending off an alligator or hot-wiring a
car--that take me through how a person could scramble or disable an
elevator car by tooling with the light beam.

This is all in the interests of a fictional story: A physics student
being chased through a building needs to make sure the elevator car
containing his pursuers never arrives at the ground floor (or the
doors never open once it does).

It's a weird question, I know, but any leads would be great.

Thanks.

---

Request for Question Clarification by journalist-ga on 08 Aug 2003 15:22 PDT

I located a magazine called "Elevator World" at
http://www.elevator-world.com/ that offers a one month subscription to
their reseach center for $15.00 - see
http://research.elevator-world.com/

See https://www.elevator-world.com/research_sub.htm#subscribe for the
details.  Their main subscription page reads in part ""The ELEVATOR
WORLD Research Center is a self-service research database offered free
of charge to current ELEVATOR WORLD subscribers."

I don't know that it would help you but it might be worth the
investment.  There's also an information request form at
http://www.elevator-world.com/findpart/door_equipment.htm that might
be helpful.

*********

A college prank concerning an elevator master key is located at
http://www.ae.utexas.edu/~london/humor/CollegePracticalJokes.html -
don't know if it might help...
"The father of my dorm roommate worked as a repairman for the Otis
Elevator Company. One weekend, I stayed with my roommate at his
parent's home. While talking with his father, we learned an _amazing_
fact: almost all escalators are reversible for use in breakdowns or
emergencies; there is usually a key-operated reversing switch located
under the handrail at each end of the escalator. We also learned a
second _amazing_ fact: most all Otis elevators and escalators use the
_same_ key."

*********

The specs for a photoelectronic switch at
http://www.hokuyo-aut.jp/pdf/PE2.pdf may be of assistance.  I found it
at http://www.hokuyo-aut.jp/products/p_sensor.htm where there are a
few photoelectronic switches.

*********

Fiberoptics regarding an elevator
"The fibre optic control unit has two connections whose function can
be set e.g. for antivalent or additional warning output signal.
Moreover, one of them can also be used as an input. As a result, the
switching signal of the input can be connected with the optical input.
Such features allow the unit to take over simple tasks of an open loop
control: With the so-called latch the electric output signal follows
the optical input for a start. When applying the electric latch signal
one can freeze the last status and process it at any later time.

"In addition, the sensor can operate like an edge triggered D
flip-flop. With the active pulse edge the currently valid switching
status is transferred to the output and maintained through to the next
active edge. This function can be used when objects are to be detected
at a defined time only.
Logic operations can be carried out as well: The output switching
signal is high when the input is activated AND the sensor detects an
object simultaneously. This feature can be used if events are to be
detected in a given time window. However, it also allows to link the
signals of two photoelectric sensors, e.g. for monitoring an elevator.
Its doors will only close if the light path of both sensors is free."

From http://www.leuze.de/english/presse/pm/p12.htm

*********

From http://www.amperite.com/examples.htm
"ELEVATOR DOOR CONTROL - It is necessary that an elevator door's
closing be delayed for a specified time after the last passenger has
entered or left the elevator. The triggered delay on release timer can
be used, in conjunction with a photoelectric sensor, to delay the
closing of the door."

*********

LAMBDA 3D protection system (a diagram is shown with brief
explanation)
http://www.unitecparts.com/portfolio/udoorpro.html



According to http://www.scanelecsz.com/photosen.html there are four
types of photoelectric sensors:

"Photoelectric switches can be divided into four groups according to
their functions. These four groups are through-beam switches,
retro-reflective switches, diffuse switches, and fiber-optics with
amplifiers. Photoelectric switches are used to detect various material
at long ranges by non-contact sensing and are manufactured to the
highest specifications and quality."

There are diagrams of each on that page.  If you were not aware that
there was more than one type, is there a particular one you would like
researched?  I hesitate to post an answer until you are satisfied with
the results.

Best regards,
journalist-ga


SEARCH STRATEGY:

"photoelectric sensor" elevator door
"photoelectric sensor" failure
"photoelectric sensor" elevator -fire
"photoelectric technology" elevator -fire
"elevator research" photoelectric
"photoelectric research" elevator -fire
"elevator technology" photoelectric
elevator photosensor technology
"elevator photosensor"
"photoelectric elevator"

---

Clarification of Question by pempek-ga on 08 Aug 2003 16:09 PDT

Those links are helpful, thanks.

The description of the different switches is good.  I think that's as
much background as I need on electric eye functionality.

I'll probably subscribe to Elevator World's research center, as well.

If you came across any other anecdotal sites--along the lines of the
college prank--those would be the most useful.  If not, don't sweat
it.

I appreciate your help.

Greetings again Pempek:

I'm delighted you found my research of assistance.  I apologize for
posting my last comments in the Clarification section as the more
appropriate place would have been in the Comments section.

I did find a reference to an elevator prank regarding Krazy gluing the
floor buttons.  I don't know how this might work for your story
but...http://www.prank.org/archive_cat.php4?catID=39

I also found a wonderful story attributed to Peter Bogdanovich at
http://www.scripting.com/mail/mail970717.html
"When the first person got on with them, Hitch [Alfred Hitchcock]
would spontaneously act like they were continuing a conversation by
saying something along the lines of, "..and it was the most disgusting
thing I have ever seen!" As people got on at each floor, Hitch would
raise the odds: "... and blood was spurting out of his mouth! Blood!
Gushes of it!"  Finally, when they were nearing the bottom, Hitch
would say "... and you know what he said to me? He raised his head up
and his last dying words were..." *ding!* and everyone would have to
get out of the elevator."  ;)

Tamarac Plaza "Elevator Malfunction" page - what to do
http://www.propertysitesonline.com/tamarac/procedures/elevator.asp

I located a parody page of "elevator tips" and it mentioned (don't
know if true) "Sometimes, photoelectric sensors are only located near
the center of the elevator door."  That got me to thinking that the
placement of the sensors in your story might be helpful with the
action.  The parody site is at http://www.monzy.com/elevator/

*********

On a search of "electronic eye" malfunction, I did locate a few
interesting links:

http://home.wlu.edu/~wendelb/Torts/1999final2b.htm
There is mentioned "The servicing procedures require inspection of the
eye mechanism and the bumpers; these were inspected and found to be
working normally. Nick Shay, the director of safety for the Fix-It
Company suggested that the problem might be with elevator's internal
diagnostic computers. He said many elevator manufacturers used
computer chips manufactured in the 1960's, which used two-digit dates
to represent the year (using "65" for "1965," for example).
Unfortunately, this engineering technique, which was necessary at the
time to conserve expensive processing power and memory resources, led
to what became known as the "Y2K" bug. As the date changed from
December 31, 1999, to January 1, 2000, the two-digit date changed from
99 to 00, confusing the chips into thinking the date was January 1,
1900. In some cases, Shay said, it is conceivable that the date
function could cause the elevator to malfunction. Shay thought that
the electronic eye and the bumper pad sensors may have turned off at
midnight, thinking it was January 1900."

From an article about fuzzy logic at
http://www.simplecodeworks.com/KSCO/book/chapter7.htm
"Even elevators are becoming fuzzy. Companies such as Otis are working
on the development of smart elevators -- devices that employ fuzzy
logic to adjust to the level of traffic. By knowing how many
passengers are currently in each elevator, which floors have
passengers waiting to board, and the locations of all of the elevators
currently in use, an optimum strategy of operation can be dynamically
achieved."

From another law case at 
http://lawlibrary.rutgers.edu/courts/appellate/a6425-98.opn.html
"The doors had two safety devices: (1) a rubber safety edge running
along the side of the doors, which was designed to retract upon
contact, and (2) electric eyes in the top and bottom sides of the
doors which would reopen them if the beam was broken by an object in
its path. The evidence indicated that these safety devices were not
foolproof. Both safety devices were functional only if an individual
or object was located between the elevator doors. The hard edge of the
exterior portion of the door could come in contact with an object or
person without activating either the electronic eye or the safety
edge."

Then this from the same report as above: "In testing the elevators,
Farrell would exert pressure on the safety edge to ensure that the
doors would retract. In addition, he would periodically check the
electric beams by using a voltage meter. The elevator in question was
checked shortly before and shortly after the accident and was found to
be in proper working order."

You may consider the plot device of substituting a "seemingly
functioning" voltage meter for use by a minor character - the worker
thinks the beam is okay because the "sabotaged" voltage meter shows
it's okay.  Then your main character could rig all he wanted without
the photoelectric beam being in use.

*******

Here follows the sum of my previous research:

I located a magazine called "Elevator World" at
http://www.elevator-world.com/ that offers a one month subscription to
their reseach center for $15.00 - see
http://research.elevator-world.com/
 
See https://www.elevator-world.com/research_sub.htm#subscribe for the
details.  Their main subscription page reads in part ""The ELEVATOR
WORLD Research Center is a self-service research database offered free
of charge to current ELEVATOR WORLD subscribers."
 
I don't know that it would help you but it might be worth the
investment.  There's also an information request form at
http://www.elevator-world.com/findpart/door_equipment.htm that might
be helpful.
 
********* 
 
A college prank concerning an elevator master key is located at
http://www.ae.utexas.edu/~london/humor/CollegePracticalJokes.html -
don't know if it might help...
"The father of my dorm roommate worked as a repairman for the Otis
Elevator Company. One weekend, I stayed with my roommate at his
parent's home. While talking with his father, we learned an _amazing_
fact: almost all escalators are reversible for use in breakdowns or
emergencies; there is usually a key-operated reversing switch located
under the handrail at each end of the escalator. We also learned a
second _amazing_ fact: most all Otis elevators and escalators use the
_same_ key."
 
********* 
 
The specs for a photoelectronic switch at
http://www.hokuyo-aut.jp/pdf/PE2.pdf may be of assistance.  I found it
at http://www.hokuyo-aut.jp/products/p_sensor.htm where there are a
few photoelectronic switches.
 
********* 
 
Fiberoptics regarding an elevator 
"The fibre optic control unit has two connections whose function can
be set e.g. for antivalent or additional warning output signal.
Moreover, one of them can also be used as an input. As a result, the
switching signal of the input can be connected with the optical input.
Such features allow the unit to take over simple tasks of an open loop
control: With the so-called latch the electric output signal follows
the optical input for a start. When applying the electric latch signal
one can freeze the last status and process it at any later time.
 
"In addition, the sensor can operate like an edge triggered D
flip-flop. With the active pulse edge the currently valid switching
status is transferred to the output and maintained through to the next
active edge. This function can be used when objects are to be detected
at a defined time only.
Logic operations can be carried out as well: The output switching
signal is high when the input is activated AND the sensor detects an
object simultaneously. This feature can be used if events are to be
detected in a given time window. However, it also allows to link the
signals of two photoelectric sensors, e.g. for monitoring an elevator.
Its doors will only close if the light path of both sensors is free."
 
From http://www.leuze.de/english/presse/pm/p12.htm 
 
********* 
 
From http://www.amperite.com/examples.htm 
"ELEVATOR DOOR CONTROL - It is necessary that an elevator door's
closing be delayed for a specified time after the last passenger has
entered or left the elevator. The triggered delay on release timer can
be used, in conjunction with a photoelectric sensor, to delay the
closing of the door."
 
********* 
 
LAMBDA 3D protection system (a diagram is shown with brief
explanation)
http://www.unitecparts.com/portfolio/udoorpro.html 
 
  
According to http://www.scanelecsz.com/photosen.html there are four
types of photoelectric sensors:
 
"Photoelectric switches can be divided into four groups according to
their functions. These four groups are through-beam switches,
retro-reflective switches, diffuse switches, and fiber-optics with
amplifiers. Photoelectric switches are used to detect various material
at long ranges by non-contact sensing and are manufactured to the
highest specifications and quality."
 
There are diagrams of each on that page.  If you were not aware that
there was more than one type, is there a particular one you would like
researched?


 
 
SEARCH STRATEGY: 
 
"photoelectric sensor" elevator door 
"photoelectric sensor" failure 
"photoelectric sensor" elevator -fire 
"photoelectric technology" elevator -fire 
"elevator research" photoelectric 
"photoelectric research" elevator -fire 
"elevator technology" photoelectric 
elevator photosensor technology 
"elevator photosensor" 
"photoelectric elevator"
"photoelectric detector" technology research 
"photoelectric detector" elevator problem 
"photoelectric sensor" technology research 
"photoelectric sensor" elevator problem
elevator pranks
"elevator door" malfunction
"electronic eye" malfunction elevator
"electric beam" malfunction elevator

Nicely done.  Your answer was very thorough and enlightening.  Much
obliged.  Additional thanks to those that posted comments/suggestions.

Most modern elevators have an "Open Door" button on the control panel
which will override the information received from the photoelectric
cell and enable the occupants to open the doors.

This may be useful in constructing a plot device involving elevators:

http://science.howstuffworks.com/elevator.htm

Here's an interesting page from Otis Elevators' website:

http://www.otis.com/modernizationdetail/1,1426,CLI1_MID9069_RES1,00.html

From the page linked above:

"The LAMBDAŽ 3D entrance-protection system uses 56 infrared emitters
and detectors to create an invisible safety net across the elevator
entrance. The microprocessor-controlled system continuously scans for
interrupted beams. If any beam in the curtain is broken, the LAMBDA
system reopens the elevator door instantly – without touching
passengers.
Features
In addition to its “curtain” protection, LAMBDA 3D features a second
protection system that projects into the hallway to detect passengers
as they approach or exit the elevator.


Objects such as dirt, dust or chewing gum can sometimes block the
emitters and detectors causing the system to shut down. LAMBDA 3D
incorporates “graceful degradation,” designed to enhance reliability
by preventing unnecessary shutdowns due to blockages."

In a MacGyverish fashion, perhaps the hero of your story can block the
IR emitters with chewing gum!

It may be interesting tangentially, though not the least bit critical,
to note that Einstein didn't actually make photoelectric technology
possible. In fact, the photoelectric effect was known for quite some
time when Einstein tackled it theoretically, which then yielded
insight into the nature of light. But the fact that light incident
upon certain metals generates a current was known and documented
sufficiently to make practical use of it, even in the absence of a
deep theory of its mechanism.

   As for the role of photolectrics in elevator doors, I'm not sure if
that's how they work these days. It seems to me that a discrete
photosensor, perhaps near the bottom, would fail to detect foreign
objects that are nowhere near the it. Thus, a human arm might get
caught in the doors and be exquisitely mangled as the carriage goes on
its merry way. It's possible to erect what's called a "light curtain",
which amounts to a detector beam that zig-zags off a series of mirrors
so that it makes its way all the way from floor to ceiling. An
interfering object will then cut off the beam no matter where it
passes between the doors. But for the life of me I can't recall seeing
any such system on any elevator I've ridden. (Maybe I'll go find an
elevator later today and check it out for sure.)

   But if that's the case, then the doors must detect obstacles by way
of the resistance imposed by the object. It'd be worth your effort to
confirm if this is right or not.

-Mark Martin

A few comments:
Your use of the term "photoelectric effect" is incorrect.  The use of
the word "effect" in this case implies the actual physical principle
involved in the operation of the photoelectric sensors.  This would be
similar to requiring our hero(ine) to use Young's modulus to break
some glass.  I would agree that this is a small nit, though.

Photoelectric sensors or arrays of them known as "light curtains" are
also used in industrial machinery to prevent operator injury.  The
number and spacing of the sensors (emitter/receiver pair) is dependent
on the level of protection required.  Elevators usually place them low
or widely spaced to sense legs and carts, which are a bigger target. 
Elevators are also generally augmented with some sort of pressure
sensor on the door so that it can detect a blockage that is not
interrupting the beam (hopefully arms and such).

Personally, I don't think the photoelectic sensor is going to develop
into a very interesting plot device.  The system is pretty dumb. 
Anything done to the elevator is going to have to be done to the
control system or the inputs to that system.  I imagine that I might
accept reading about your hero rewiring the photoelectic sensor so
that it forces the doors closed if the beam is broken.  They can then
jam a piece of cardboard in between the doors on the special floor.

Of course, if they are having to rewire or reprogram, they could
theoretically do just about anything, but it would require specific
elevator knowledge and/or programming equipment.

Perhaps they can instead trip the fire alarm input to the elevator
system (not the whole building) so that the elevators return to the
lobby and cannot be used without a key.  I could imagine this being
done with a single piece of wire (properly placed).

Or, they could rewire the buttons on the panel so 4 actually brought
you to 3, etc.

Bradley

Dear Pempek:

Thank you for your rating, comments and added generosity!  I'm
delighted you are pleased with my answer and I wish you great success
with your book.  :)

Best regards,
journalist-ga