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| How do you prove an LED is actually lit? |
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| floobydust:
Sort of a similar application is flame detection/combustion monitoring in large burners. A UV photodiode or more typically a Hamamatsu discharge tube is used with a viewing port on the flame. To meet functional safety requirements, there is a self-check whereby you turn a UV LED on and off, while watching the sensor's response. This confirm things are not blocked by soot, dirt etc. or that there is a hardware failure. Some implementations use a shutter you can pop up to cover the sensor. OP would have troubles with the extra hardware and conductors in the cables to the gate arms. I can't see monitoring the lamps as being necessary because there are redundant sets at a rail crossing. Monitoring the LED current & voltage would give a lot of coverage, I've only once seen a red LED fail that almost faked the correct VF. Sunlight would be a problem with phototransistor-based monitoring. I'm told most crossing still use primitive relay logic for the lamps/gate arms. OT: The UVTRON would make an awesome kitchen fire alarm, it can detect a candle flame 20m away, across a house, sunlight and smoke is ignored. |
| james_s:
--- Quote from: floobydust on January 27, 2023, 08:33:52 pm ---OP would have troubles with the extra hardware and conductors in the cables to the gate arms. I can't see monitoring the lamps as being necessary because there are redundant sets at a rail crossing. Monitoring the LED current & voltage would give a lot of coverage, I've only once seen a red LED fail that almost faked the correct VF. Sunlight would be a problem with phototransistor-based monitoring. I'm told most crossing still use primitive relay logic for the lamps/gate arms. --- End quote --- Nobody said anything about gate arms. From what the OP has said this is for railroad signals, ie traffic signals for the trains, not crossing signals for motorists. Railroad signals are quite specialized, traditionally they were kerosene lamps, then gradually they were electrified, initially using batteries as they were often installed in remote locations. |
| IanB:
--- Quote from: james_s on January 27, 2023, 08:49:17 pm ---Nobody said anything about gate arms. From what the OP has said this is for railroad signals, ie traffic signals for the trains, not crossing signals for motorists. Railroad signals are quite specialized, traditionally they were kerosene lamps, then gradually they were electrified, initially using batteries as they were often installed in remote locations. --- End quote --- Indeed this, and from the context I would assume it is for a heritage railway, where funds are likely to be less abundant than at a mainline railway. |
| jmh:
--- Quote from: IanB on January 27, 2023, 09:21:13 pm ---Indeed this, and from the context I would assume it is for a heritage railway, where funds are likely to be less abundant than at a mainline railway. --- End quote --- Yes it is a heritage line - mostly our own money or what we can scrounge. --- Quote from: james_s on January 27, 2023, 08:49:17 pm ---Railroad signals are quite specialized, traditionally they were kerosene lamps, then gradually they were electrified, initially using batteries as they were often installed in remote locations. --- End quote --- And we still use kerosine lamps sometimes where there is no power, although a rechargeable 12V battery and a single LED lasts for several weeks. But those are in some of the mechanical signals. |
| jmh:
Just in case it's remotely of interest this is one of the lamps taken out of it's housing. |
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