I'm sure the exact answer is variable but is the response time in milliseconds and is it dependable under stable conditions? If I put 2 PIR's on my front fence and measured the time between responses as a car went past, will the system respond quickly enough for me to calculate the speed of the car?
2006-09-22 00:45:29 · 5 answers · asked by Paul D 3 in Science & Mathematics ➔ Engineering
It all depends on the weather conditions, the quality of your lens, and of course the PIR's aim. Its aim is also affected by the shape of its "target". A speed radar for example, is unlikely to engage a motorcycle from the front due to its presentable area.
Now, about speed measurement; in theory if you are "quick" enough you should be able to measure it but not accurately due to aforementioned factors. That's why the majority of speed control points have road marks, to indicate the "distance" part of the formulae.
But you may have fun in trying.
All the best.
2006-09-22 00:57:10 · answer #1 · answered by Cos 2 · 0⤊ 0⤋
I don't even know what a PIR detector is, but if you are trying to measure the speed of a car going by two detectors it doesn't matter how quickly they respond. What matters is the variation (and consistency) in response time in the two units you are using. Example. If the response time is always exactly an hour, when a car passes the first detector will respond in one hour. The second will respond in one hour plus the time it took the car to travel to the second detector. You can still subtract the times and obtain how long it took for the car to travel the distance between the two detectors. The problem comes in if the detector takes a variable amount of time to respond. You could even compensate if one detector responds much faster than the other as long as you know the response speed and it is consistent.
2006-09-22 01:00:27 · answer #2 · answered by Randy 3 · 0⤊ 0⤋
Sounds like you are trying to catch idiots speeding along your road. PIRs may not work. The security ones are looking for body heat.
If you are trying to see how accurate your speedometer is, stop and make friends with the next manned speed trap you see. They aren't accostomed to seeing a friendly face and will probably help you out.
2006-09-22 01:03:19 · answer #3 · answered by upf_geelong 3 · 1⤊ 0⤋
bad plan, birds, two vehicles can go by at the same time, squirrels, people walking their dog at the same time a car goes by will throw your readings out, also to get a true reading you'd have to patch both pir's onto one circuit board in order to get decent consistency.
You'd be better off videoing the vehicle between two fixed points over a predetermined time scale and work out the speed from that. Easiest way would be to use the timer on a handheld video camera and display it on screen while shooting.
2006-09-25 10:44:48 · answer #4 · answered by cedley1969 4 · 0⤊ 1⤋
each and every PIR i've got put in required a impartial,maximum are double insulated(image of sq. interior a sq.) so do not want an earth,yet not good coaching to apply earth as impartial,as no risk-free practices to cable. yet once you so want it is going to artwork utilising earth as impartial,yet my difficulty could be why have you ever misplaced a conductor? are you able to rewire? try 3core with Insulation res.tester first as would desire to be greater problems with cable.Is it purely a %capathene 3core that's buried?If sodon'tt use because it is going to rot in damp floor.
2016-12-15 12:14:34 · answer #5 · answered by ? 3 · 0⤊ 0⤋