Author Topic: Simple DCC Detection Switch Position Sensing  (Read 1104 times)

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davefoxx

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Re: Simple DCC Detection Switch Position Sensing
« Reply #15 on: October 04, 2021, 11:49:49 AM »
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The light is lit when the switch is open.

If I understand what you mean by this statement, shouldn't you consider the light being lit only when the switch is in the "normal" position, as a failsafe?  In other words, if the bulb burns out, it would then be assumed that the switch is thrown and trains would not barrel into a turnout thrown the wrong way.  In your example, a burned out bulb indicates that the switch is aligned for the main route.  Did I get this right?

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Ed Kapuscinski

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Re: Simple DCC Detection Switch Position Sensing
« Reply #16 on: October 04, 2021, 12:57:21 PM »
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If I understand what you mean by this statement, shouldn't you consider the light being lit only when the switch is in the "normal" position, as a failsafe?  In other words, if the bulb burns out, it would then be assumed that the switch is thrown and trains would not barrel into a turnout thrown the wrong way.  In your example, a burned out bulb indicates that the switch is aligned for the main route.  Did I get this right?

DFF

You've got it somewhat backwards.

The goal is to indicate to the crew on the ground that the system will not allow the DS to clear things up before they leave the location. Aside from the light (and without eating up its own detection block), there's no practical way for anyone to know what the situation on the ground is because the equipment in the block will also be shunting the circuit and indicating that the block is occupied. The light is a reminder to lock things up before you depart. The signals at the end of the block are what prevents a train from barreling through an open switch. They won't display anything other than a "stop" if the switch is open or the box unlocked. Of course, they'll also be displaying a "stop" indication if there's equipment in the block (which will almost always be the case when the crew is in the area).

If I were designing a true safety critical implementation, I'd have a green LED that was lit when things would report "clear", but that's what the signal system is for. The light is more about "hey dummy, don't forget about me" than anything else.