Binu Pillai rediffmail.com> writes: > Hello All > I am looking for ultrasonic or say any other sensor for anticollision system > for loco moving at a very very > slow speed. Is there any suggestion for any good product for the same. What is 'very reliable' (what happens if it kills one in 200 workers) and how much time do you have to react. Since everything is made of metal in there magnetic sensing seems to be the best way to go, apart from wiring the rail side with a magnetic loop indexing system. Works even in darkness and under water ... why does it have to be ultrasound ? If the thing that moves at 3km/h has to make a decision based on the sensor reading how much time does it have for that ? Iow, if it's a 40ton load at 3km/h you will have to look ahead for about 10 meters at least if you want to stop in time. Ultrasound will not work well at 10 meters in a noisy environment with heavy vibration of the equipment (worsens the response and dithers the return echo out of the receiver's tuned band due to doppler). Dust in the air disperses ultrasound (steam does it too) by the way. Also how big is the something you are about to hit and what is it made of. Metal car ? Person ? Animal ? A wire ? A chain ? A metal rod ? So what do you need: a) a reliable distance measurement system, reading in what (10cm/10 meters is 1% - this begins to be seriously accurate and can be made reliable only by indexing the way somehow - probably inductively) b) a reliable relative distance measurement (harder than above) c) a reliable way to know your loco is about to hit something 10 meters away with +/- 50cm precision (5% - fairly easy but more likely with microwave than with ultrasound). d) other Electronics work great at 90deg C and above but usually using extended temperature parts, and no electrolytic caps. This is not a serious limitation for what you need imho. Vibration is a much worse limitation, and metal dust can be a big problem together with condensing steam and sulfur gases. hope this helps, Peter -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist