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Author Topic: More on electric staff instruments
AJRM
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Post More on electric staff instruments
on: February 11, 2012, 08:59
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Paul Horder has provided some additional information on electric staff instruments including a close-up photo of the top of the staff machine.
Below is a photo taken in the signal box at Cooma showing the out-of-use instrument which used to control the section from Michelago to Cooma. This instrument is presently unpowered, without staves and is no longer connected to another instrument; hence the indicator is in a neutral position.

Paul writes: From memory, electric staff instruments were usually powered by wet cells as there was no mains power. The cells only produced a small voltage at low current. To reduce power consumption, current only flowed between instruments when a staff was inserted or withdrawn. To withdraw a staff, signallers exchanged bell codes about the type of train using the bell key on the instrument. After the last beat, each held the key down and the meter should deflect to 'staff in' to indicate either could withdraw a staff. When a staff was withdrawn or inserted the polarity on the two wires between instruments reversed so each knew whether a staff was in or out. When the staff was removed the meter responded to a change of polarity and showed 'staff out'.

Image

liverpoolr-
ange
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Post Re: More on electric staff instruments
on: May 6, 2012, 11:47
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I am very much interested in trying to replicate the operation of electric staff instruments for use on my layout. I have access to a document that shows the electrical schematic of how they operated, but even with my electrical background, it seems a bit beyond me, especially how to replicate it in model form.

My idea is to possibly simplify the circuitry just to provide interlocking preventing the removal/insertion of 'staffs'.

Anyone out have any ideas?

Cheers,

Ian

AJRM
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Post Re: More on electric staff instruments
on: August 18, 2012, 00:50
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Hi Ian,
There is an article in Model Railway Journal #215 (in newsagents now) which describes how minature block instruments work and a further article that provides some circuits to replicate their function in model form. I'm not sure these are directly relevant to what you want to do, but they might give you some ideas.

Stephen

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