basement-traction/ selector questiongreenspun.com : LUSENET : Elevator Problem Discussion : One Thread
Hi, I am not an elevator pro, but elevators are a huge hobby/interest of mine. I lurk around this BBord (and the elevator-world bord too) and from reading your psots I have learned an incredable amount about the basic operation of these great machines which interest me so much.
I just would like a little clarification on 2 questions: I'm a little un-clear on the porpose of the selector in elevator control. Could someone just give me a breif description of how they work and what they do. (Are they still uned in modern microprosor controled systems?)
My second question is why would a basement-traction set up be prefered to overhead? are basement machines still instaled today or have they become sort of a dinosaur?
Thanks in advance for taking time to answer! My e-mail is legit... so feel free to e-mail me personaly if you like
-- Christopher (Parsifal96@aol.com), November 02, 2003
Mechanical Floor selectors are no longer used....although a lot of companies didnt use them anyway....modern mircoproccessor dont have any need for them its all done in the software by inputs from inductors in the shaft or an encoder type arrangement either on the machine or driven by a toothed tape in the shaft, there may be others..and I will be corrected i'm sure :)
Basement machines are/were usually used because there doesnt have to be a machine room sticking out at the top of the building...or height restrictions and the builders want max floorspace.....nowdays with the machineroomless type elevators it really does away with the need for basement machines anyway.
-- dayle (email@example.com), November 03, 2003.
Everything Dayle said was correct, but maybe I can help add to the picture a little on selectors.
Floor selectors, depending on the model and make of the elevator, did a few things. Firstly, they ascertained car position in the shaft. Whether activated electrically by inductors in the shaft, or mechanically by means of a metal tape attached to the car itself, the selector " carriage " moved as the car moved, which usually activated switches that the controller used for, amongst other things, car position, when to initiate slowdown, door zone, traffic zoning, and much more. The selector was also used for direction setting. If a mid shaft up hall call was placed, the controller needed to know which direction to send the car in order to answer the hall call. If the car was near the top of the shaft, it would have to know to send the car down to answer that call. One ingenious way this was done was to have normally closed switches wired in series, one for each floor. As the car, and selector carriage, moved up the shaft, it would mechanically open these normally closed switches. Now, if a car call was placed, say, at floor 10, and the car was at floor 2. The positive feed would travel down this chain of normally closed contacts until it found the open switch at floor 2. Because the feed could not go down, it would travel back up a wire mounted on the selector carriage itself, to the up direction relay. The same thing happened in the opposite circumstances.
Like I said earlier, different makes and models did different things. The basic functions of most of them were as I have described above. Being somewhat younger member of this profession, I have to marvel at how ingenious these things actually are. What is now done by a microprocessor and photocell, used to have to be done by complex mechanical and electrical means. A handful to maintain, especially as they age, they are none the less, amazing. The knowledge of how to set them up is fast disappearing, with the older guys retiring and taking their knowledge with them.
Hope this helps Christopher !
-- Justin Ward (firstname.lastname@example.org), November 04, 2003.
hey..not so much of the old thanks...im still relatively young (mid 30s) and have had a fair bit to do with the mechanical selectors...although very happy a lot have now been pulled out and modernised..but a some of the building owners cant see past the dollars and persist with the selector etc....and they can also be a REAL!!!! nightmare when you get an intermittant fault..i.e. direction setting...especially in a group situation when the selector still has "live" parts even though the main switch is off
-- dayle (email@example.com), November 05, 2003.
Dayle, when you're my age, anything over 30 is OLD ! However, I'll get there one day.
Probably my 3 favourite selector faults are:
6850BJ 1) dodgy solder connection on a HCC 2) residual magnetism on the PM 3) the SRC contact not always springing back after going past a brush.
Express MH 1) bakelite arms breaking 2) dmu and dmd pawls going residual 3) spring steel tension plate not springy anymore
Grants 1) advancing too much 2) advancing too little 3) base not screwed down tightly !
-- Justin Ward (firstname.lastname@example.org), November 05, 2003.
As for the selectors, I've worked on quite a few. I am in my 30's, but still have many around with generally flawless performance, as long as they are regularly inspected, adjusted, and not allowed to wear out (takes time and money that aren't nearly enough in most service contracts). I've worked on the venerable Otis 6850 (with and without the advancer panel), K.M. White (On Dovers and Armor's with the really cool solid brass pegs, and blades), Dover's horizontal (with the optical pie plates), Montgomery's selector with the microswitch dump switches, Armor's cartop mounted KM White with not only the blades and pegs, but a microswitch/pie plate arrangement that is sheer simplicity, and a signal machine for an old Llewellen that utilizes a finger contact dipping into a crucible full of Mercury to make the contact. And that's just the stuff that's still in service! After many years of studying, as well as working on such equipment (old times, hold on to your hats) as reactors, regulators, selectors, and a really cool Otis self-excited generator circuit that utilizes 1/2 of the hoist motor as a motor, and 1/2 as a generator for the generator shunt field, I have come to the conclusion that they were creating art, not cheap, replace it in 6-10 year, throw-away stuff. While I am not impuning the current output of the industry, the facts are that the new stuff is designed with a set lifespan, period. The old stuff was sold by the pound, and the fact that stuff 30-50 (or more) years old still runs reliably with careful maintainence, says something for the folks who built and designed it. Dwell well, and keep up the good work. S.
-- Steve (email@example.com), November 06, 2003.