[seqpg] Re: Thoughts for a mates project

  • From: "justin" <justin.adams@xxxxxxxxxxxxxxx>
  • To: <seqpg@xxxxxxxxxxxxx>
  • Date: Tue, 28 Apr 2009 23:46:53 +1000

Limit Switches
Limit Switches are the most numerous input devices in an elevator. They tell 
the system the position of gates, doors, turnheads, or distributors, and the 
alignment of belts. A switch can only tell whether an object is present or 
absent at a certain location. A pair of switches can tell if a gate is 
completely closed or fully open, but not where the gate is if it is somewhere 
between those two limits. A limit switch can be operated by mechanical contact, 
by breaking a beam of light, or by detecting the disturbance of a magnetic 
field caused by a metal object.
The following diagram shows a mechanical limit switch wired to a pair of 
indicator lights. It has an actuator arm which operates the switch contacts 
when it is moved slightly by contact with a piece of equipment such as a slide 
gate. The arm is spring-loaded, so it returns from its actuated position to its 
normal position when the equipment moves away. In the diagram, you can operate 
the limit switch by moving the arm with a mouse. 


A limit switch has at least two sets of contacts: "Normally Closed" (NC) and 
"Normally Open" (NO) . When the switch is in the normal position (nothing 
touching the arm), the Normally Closed contacts pass electricity, so the 
diagram shows the Normally Closed indicator light as lit. When the switch is in 
the actuated position, the Normally Open (NO) contacts pass electricity, so the 
Normally Open indicator light is lit. The "Common" wire carries electricity to 
both sets of contacts. The terminology of switches is the reverse of the 
terminology of gates: Switch contacts let electricity pass when they are 
closed. A gate lets grain pass when it is open. If you have a browser for 
Virtual Reality Modeling Language (VRML), such as Cosmo Player from Silicon 
Graphics, you can operate an interactive 3-D model of the gates and limit 
switches under a shipping bin. VRML browsers normally require Windows 95 or 
Windows NT. 

  ----- Original Message ----- 
  From: VK4UTE 
  To: seqpg@xxxxxxxxxxxxx 
  Sent: Tuesday, April 28, 2009 8:55 PM
  Subject: [seqpg] Thoughts for a mates project

  Hi All

  Here's one for the think tank.....
  One of the guys a work is building a house [and on a very steep hill by the 
sounds of it.]

  He wants to install a 3 stop dumb waiter from the kitchen (Top floor) via the 
laundry (gnd floor) to the Garage. (basement)
  for shopping. I believe the original plan had the void as a laundry chute and 
he has just reversed the access from the
  linen press to the pantry so it can be used for groceries as well as clothes.

  He is thinking about a gate controller and motor (The sliding kind) as it has 
already got stops for full open, full closed and partial
  open option for pedestrian access.

  I was thinking about the cheap winches from the automotive shops and a PLC 
(programmable logic controller) as some year ago
  I saw a developer board that had reversible high amperage mosfet motor 
control plus switch and sensor inputs. Plus this has some software
  so it could be programmed by drawing a flow chart.

  NOTE: A real electric dumb waiter set-up would cost more than hiring a 
teenager to carry the shopping upstairs weekly for about 7 years.


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