31 replies to this topic

[EagleAce]

Quote

some of you may have seen the GO switch located on towers, near guide sheaves, etc.- that's a magnet held in place by the presence of the haul rope. If the rope were to move away from the sensor, the magnet drops and trips the teeny little switch inside

that's what Eagle has. IIRC Dodge Ridge's Yan has pc board-type brittle bars

[Emax]

liftmech, on Nov 28 2003, 05:12 PM, said:

Technically, it's not, although for practical purposes that's what everyone calls them. A sensor is a type of switch that does not need to be replaced if the condition it is meant to sense happens. For example- some of you may have seen the GO switch located on towers, near guide sheaves, etc.- that's a magnet held in place by the presence of the haul rope. If the rope were to move away from the sensor, the magnet drops and trips the teeny little switch inside. A brittle bar is a glorified wire that, when broken, must be replaced- which can be a time-consuming job, depending on where the bar is. :P Doppelmayr loves the things.

Despite the risk of being thought nitpicky, that isn't how General Equipment Corp.'s "GO Switch" works. It uses a spring-loaded magnetically biased mechanical contact. The contact closes when the magnetic field is altered by the close presence of a ferromagnetic mass. When the mass is removed, the mechanical switch opens. The magnet does not move. Buy one and take it apart - they're still for sale. Google GO switch.

Phil Berger's (Enduratec) switch worked in a similar manner, but used rare earth magnets and a glass reed switch.

Proximity switches that use "moving magnets" are generally undesirable because they usually depend upon gravity for proper operation. Yan's RPD and my own CPS switch fall into this catagory.

Phil Berger's (Enduratec) switch worked in a similar manner, but used rare earth magnets and a glass reed switch.

Both of these switches were problematic due to too short a sensing range for rope detection use.

This post has been edited by Emax: 11 August 2007 - 04:00 PM

[liftmech]

You're not being nitpicky, you're correcting my assumption. Thanks for the clarification. I've read service bulletins sent out about your CPS switches, they mention the dropping of the magnet for correct operation.

Now- slightly off-topic but when I test the GO switches I've got a bolt drilled through a long piece of EMT. I place the bolt right next to the switch and it opens. If it's not the magnet being attracted to the bolt because it's closer than the rope, then how is this test working? No-one explained the 'why' of this test when they showed it to me, just the 'how'.

[Emax]

liftmech, on Aug 12 2007, 08:04 PM, said:

You're not being nitpicky, you're correcting my assumption. Thanks for the clarification. I've read service bulletins sent out about your CPS switches, they mention the dropping of the magnet for correct operation.

Now- slightly off-topic but when I test the GO switches I've got a bolt drilled through a long piece of EMT. I place the bolt right next to the switch and it opens. If it's not the magnet being attracted to the bolt because it's closer than the rope, then how is this test working? No-one explained the 'why' of this test when they showed it to me, just the 'how'.

What the bolt does is warp the field of the magnet, changing the force applied to the switch contact. The Go switch (at least the original one) and Phil's prox wsitch are unique in this respect. You're right about the magnet drop in my switch.

I wasn't able to quickly find the patent for the GO switch, but here's a link to Phil Berger's patent. The swithes are very similar on operation.

http://www.google.com/patents?id=6b41AAAAE...+switch#PPA1,M1

This post has been edited by Emax: 12 August 2007 - 07:49 PM

[liftmech]

Thanks.

[Razvan]

The pics are no longer displayed in the posts. Can someone upload them again? Very interesting concept, them bulbs, and any other use of unintended technology.

Curious latecomer.

[Emax]

Razvan, on 25 December 2010 - 02:27 AM, said:

The pics are no longer displayed in the posts. Can someone upload them again? Very interesting concept, them bulbs, and any other use of unintended technology.

Curious latecomer.

I'll post them again. The State of Utah folks were not impressed. I think it's a great idea. No doubt about breakage - common part that can be purchased anywhere.

[Emax]

Razvan: here are the photos again. One of them shows the problem with the original (factory) design - the wires twist together in a place that cannot be seen.




The device mounts via potted-in magnets. Easy to place, very strong mounting.
The lamps are available in a variety of lengths and their resistance is VERY low, so they're pretty much invisible to the system.
Very positive circuit interruption.

Down side: glass fragments

Here's the original post that explains the project:

Actually, it's just a brittle bar - that is decidedly brittle. Halogen bulbs are used - because of their convenient shape. The magnets serve only to hold the assembly to the sheave train.

As you know, we have YAN lifts - and therefore we have DR-2s, DR-3s and DR-4s... very early "brittle bars". Inspections have revealed that:

1. Most of the bars have lost their "brittleness" - making them less likely to actually break the circuit when needed.
2. Many of the bars removed had glass-brittle insulation on the wire leads - much of which had broken away, leaving the two wires exposed. This happens at the entry point into the "boot" of the switch... where it cannot be easily seen.
3. Several of the switches with bared wires had those wires twisted so as to create a connection ahead of the switch - making the bar a bypassed device. This is really bad.

I have rebuilt all of the DR switches on all of our lifts - replacing the "boot" with a new one, using teflon insulated wire and a 2-pin connector about 2 inches from the switch. The teflon wire does not become brittle with exposure to UV radiation. The connector allows the switch to be changed out easily - without the need to pull yards of wire through the crossarm.

The rebuilds fix what was wrong... everything except the questionable "brittleness" of the thing. It seemed to me that if you really want brittle, use glass. Ever busted a light bulb without breaking the filament? The need to easily retrofit drove me to the magnets - you can place it anywhere and it will stay there. Halogen lamps come in a variety of lengths and are cheap if you shop well. The latest version of the halogen switch uses one lamp and one length of Garolite along side - for strength. These two are glued to the magnets (UV-cure adhesive) prior to a dip in 3M Scotchcoat and later in neoprene tool dip. The finished assembly is durable, easily mounted and has a very low profile. The profile is important because the original DR switches often get nicked by grip bolts in windy conditions. The lower profile eliminates this problem.

This post has been edited by Emax: 27 December 2010 - 09:03 AM

[Razvan]

Thank you, Bud! Very ingenious.
Can't imagine though how it's in the "deployed" mode. Do you happen to have a picture of it on the tower? (or of the original un-brittle bar)?
Most glass fragments can be contained if the whole bulb is dipped in neoprene - if there's any that's UV resistant. This shouldn't affect too much the brittleness.

[Emax]

Here are some of the variations. Notice that some are fully dipped in neoprene - you're right, it does contain the glass.



Here is another possibility. A copper-clad (hollow) air arc rod makes a pretty good element too. The through-hole can be slightly enlarged at the ends to perfectly fit a standard banana plug.
The far end uses a banana "shorting plug" while the home end uses a male-female standard plug. Putting a standard banana plug on the end of the cross-arm wire provides a clean and inexpensive quick disconnect. Magnet mounting again, of course.

[Razvan]

Being familiar only with the current Doppelmayr break forks (and beginning to learn about Leitner's), I can't imagine how it's mounted; why magnets on both ends.

Do the bulbs glow during lightning storms? ;-)

[Emax]

Razvan, on 27 December 2010 - 01:47 PM, said:

Being familiar only with the current Doppelmayr break forks (and beginning to learn about Leitner's), I can't imagine how it's mounted; why magnets on both ends.

Do the bulbs glow during lightning storms? ;-)

Sticks to the rocker assembly directly beneath the rope - in our application. the magnets are very strong, so 1-ended "sticking" would work just as well.
Not all "break fork" applications depend on the rotation of the assembly. As soon as I can talk someone into grabbing a photo of a typical installation, I'll post it.

A good rule of thumb is: if you see the bulb glowing, take cover quickly!