# How does the old LGB chuff sensor work?



## Chata86 (Dec 5, 2010)

I have my early 80s 2080S open for service. I'm in the middle of fixing the analog sound system, but in the midst of that I started wondering exactly how the factory chuff sensor works. It has two green connectors with two conductors each. Each one goes down to these glue blobs under the motor. In between these sensor blobs is a metal (surprisingly non magnetic) disc that's shaped a bit like a rectangle with rounded edges. It's driven 1:1 from the center wheel on the locomotive. So I suppose that means it activates two times per revolution of the wheel. That's interesting because I think I've read about people setting up for 4x with their aftermarket digital systems. 


Anyway, what's in the glue blobs? I expected to see a magnet and one reed switch. Instead there is no magnet and two switches. I don't get it.


PS: Keeping track of the two little ball bearings at each end of the motor's axle is very tricky! I've never opened the engine this much before.


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## K27_463 (Jan 2, 2008)

LGB has always used hall effect sensors for chuff trigger. Yes, you are correct it- triggers twice and should be 4 times per revolution to be correct. 

Lots of info on line about how hall sensors work. They work fine in this application- though not compatible at all with other sound systems. They are just another example of LGB going their own way on things, and if a little complexity is good,m, then more is always better..... 

jonathan/EMW


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## Dan Pierce (Jan 2, 2008)

Think of one side being a magnetic transmitter and the other side as a receiver. The metal tab breaks the magnetism path. 
On the receiver side you can just use a reed switch and resistors to make a false grounding of the signal. 

Newer motors do not need the thrust ball bearings and these must be removed when replacing the motors.


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