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| How do you prove an LED is actually lit? |
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| AVGresponding:
The problem with any current sensing method is that you just can't rule out a failure mode where there's an approximately normal current flowing. The only way I can see meeting the criteria is to directly sense the light output, and even that has its problems. What if the sense circuit fails in such a way as to give a false good reading? |
| jmh:
--- Quote from: AVGresponding on January 28, 2023, 10:54:39 am ---The problem with any current sensing method is that you just can't rule out a failure mode where there's an approximately normal current flowing. The only way I can see meeting the criteria is to directly sense the light output, and even that has its problems. What if the sense circuit fails in such a way as to give a false good reading? --- End quote --- From what everyone has been saying yes I think sensing the light output is the best way here. At the end of the day its about risk management and mitigation and what The Management agree to. All we can do is give options. Now don't shoot me for not building my own but I found a little relay module on a certain auction site which is trigged from a photosensor which will do exactly what we need. At least it's something I can experiment with and only a few quid. And not my money this time. When I am next there we do have a LED replacement unit from a 'real railway' signal and I'll have a closer look to see how that works. Those are very different signal lamps to our old thing and replace bulbs which are a lot more watts. |
| AndyBeez:
--- Quote from: AVGresponding on January 28, 2023, 10:54:39 am ---What if the sense circuit fails in such a way as to give a false good reading? --- End quote --- :o Then simply replace all of this clever technology with the Mark One eyeball. --- Quote from: jmh on January 28, 2023, 11:35:04 am --- I found a little relay module on a certain auction site which is trigged from a photosensor which will do exactly what we need. At least it's something I can experiment with and only a few quid. And not my money this time. --- End quote --- So how will you notify the signalman that any light source is out of operation? How do you force a failsafe or stop condition on the block? |
| jmh:
--- Quote from: AndyBeez on January 28, 2023, 12:29:41 pm ---So how will you notify the signalman that any light source is out of operation? How do you force a failsafe or stop condition on the block? --- End quote --- That's the easy part. LED fails, relay drops, drops the control relays in all following signals which then go to red (their default). Driver stops the train and calls to see what is wrong. Showing anything other than red is always a positive action i.e. a relay is energised to do so. |
| PA0PBZ:
--- Quote from: IanB on January 27, 2023, 11:44:46 pm ---On the other hand, given that the indicated price is £1.45 per bulb... --- End quote --- I didn't trust the site: quantity 10, price each £ 14.50. And indeed, clicking the 'add to cart' button presents you with the total of £ 145.00 |
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