|
|
Thread Tools | Display Modes |
#21
|
|||
|
|||
Traffic Loop Sensor Trigger For Bikes
In article
, Jay Beattie wrote: On Nov 11, 6:48*pm, Mike Rocket J Squirrel wrote: On 11/11/2008 6:34 PM Patrick Lamb wrote: On Tue, 11 Nov 2008 16:52:11 -0800, Mike Rocket J Squirrel wrote: On 11/11/2008 1:56 PM Arthur Shapiro wrote: Would the presence of a strong magnet affect these sensors? *I don't appreciate the behavioral distinction between magnetic flux and metallic mass in the situation in question. I'm not anxious to add extra riding weight, but these fancy new rare earth magnets can pack a huge effect in a couple of ounces. Art Nope -- AC induction loop doesn't care about magnetic fields. All the loop would "see" is the metal of the magnet, the field would be invisible. Is there a single common frequency that all these things use? *I've toyed with the idea of building a light weight circuit with a small antenna to disrupt the flux, but I don't care enough to build much smarts into the system. Dunno. If you're smart enough to build a circuit to counter the signal in the loop, you're smart enough to hook a small loop to a battery-powered oscilloscope and plunk it atop the sensor loop to see what it picks up. I have a friend who says that if the light does not turn green, you can treat it as broken and proceed through the intersection when safe. I have not been able to find any support for this statement in the UVC. -- Jay Beattie. The basic principle is this: a light system that does not properly detect traffic is de facto broken. The UVC does have a standard for non-functioning traffic lights: treat as a four-way stop. Bikes are traffic, so if the loop can't detect you, it's not working as expected. Note that the key difference between this broken intersection and most others is that the cross traffic doesn't know it's broken. Nonetheless, traffic laws are not meant to be a death sentence. You aren't expected to wait at the light until dehydration ensues. That said, let's be realistic: there are busy intersections where, laws be damned, the only rational choice may be to give up and activate the pedestrian signal. -- Ryan Cousineau http://www.wiredcola.com/ "In other newsgroups, they killfile trolls." "In rec.bicycles.racing, we coach them." |
Ads |
#22
|
|||
|
|||
Traffic Loop Sensor Trigger For Bikes
On Nov 11, 11:23*pm, Jay Beattie wrote:
I have a friend who says that if the light does not turn green, you can treat it as broken and proceed through the intersection when safe. *I have not been able to find any support for this statement in the UVC. * Hmm. I suppose an alternative strategy would be to stand there and wait for a traffic light repair crew. Or wait for starvation, whichever comes first. Anybody have a report of someone ticketed for treating a non- functioning signal as broken, then proceeding when safe? - Frank Krygowski |
#23
|
|||
|
|||
Traffic Loop Sensor Trigger For Bikes
On Nov 11, 11:25*pm, peter wrote:
On Nov 11, 6:34*pm, Patrick Lamb wrote: On Tue, 11 Nov 2008 16:52:11 -0800, Mike Rocket J Squirrel wrote: On 11/11/2008 1:56 PM Arthur Shapiro wrote: Would the presence of a strong magnet affect these sensors? *I don't appreciate the behavioral distinction between magnetic flux and metallic mass in the situation in question. I'm not anxious to add extra riding weight, but these fancy new rare earth magnets can pack a huge effect in a couple of ounces. Art Nope -- AC induction loop doesn't care about magnetic fields. All the loop would "see" is the metal of the magnet, the field would be invisible. Is there a single common frequency that all these things use? Don't think so. *They're generally in the 20 - 40 kHz region but AFAIK it's not standardized. BTW, the advantage of iron for E-M induction is primarily at very low frequencies. *At typical loop detector frequencies non-magnetic metals work just as well. *So aluminum bikes and rims are equally effective as steel ones. *The problem is just insufficient quantity unless the detector sensitivity is turned up. Do you know the frequency that industrial inductive proximity sensors use? I ask because those are definitely less sensitive to aluminum than to steel. (Unless the aluminum is thin foil, oddly enough.) - Frank Krygowski |
#24
|
|||
|
|||
Traffic Loop Sensor Trigger For Bikes
On Nov 12, 8:08*am, Frank Krygowski wrote:
On Nov 11, 11:23*pm, Jay Beattie wrote: I have a friend who says that if the light does not turn green, you can treat it as broken and proceed through the intersection when safe. *I have not been able to find any support for this statement in the UVC. * Hmm. *I suppose an alternative strategy would be to stand there and wait for a traffic light repair crew. *Or wait for starvation, whichever comes first. Anybody have a report of someone ticketed for treating a non- functioning signal as broken, then proceeding when safe? And for Ryan, could you give me a section number for the UVC or the langauge -- I am trying to find a cross-reference under the Oregon version of the Code. So far, I have only found a case where someone who went through a "stuck" red light and got hit sued the city. The court noted that the city should assume that a driver at a "stuck" red light will go through it eventually. It cited to the general statute about following traffic control devices but did not cite any section about how people are supposed to treat malfunctioning devices. In fact, our version of the UVC makes it clear that it is an infraction to go against a light unless ordered to do so by a police officer. The section where you would expect to see an exception for malfunctioning devices says nothing about them. -- Jay Beattie. |
#25
|
|||
|
|||
Traffic Loop Sensor Trigger For Bikes
On Nov 12, 11:08*am, Frank Krygowski wrote:
On Nov 11, 11:23*pm, Jay Beattie wrote: I have a friend who says that if the light does not turn green, you can treat it as broken and proceed through the intersection when safe. *I have not been able to find any support for this statement in the UVC. * Hmm. *I suppose an alternative strategy would be to stand there and wait for a traffic light repair crew. *Or wait for starvation, whichever comes first. Anybody have a report of someone ticketed for treating a non- functioning signal as broken, then proceeding when safe? - Frank Krygowski No ticket, but I've been stopped and warned, and told I should use the crosswalk and walk across in the future. I didn't feel like arguing at the time, so I let it go and went on my way. The intersection in question had 2 lanes coming from my left, in a 35MPH zone that just came down from 50, and 3 lanes from my right, also in a 35. Personally, crossing that intersection I'll take the extra speed of the bike every time. Had I been on the shoulder and crossed as a pedestrian, even using the bike, he probably wouldn't have bothered me. |
#26
|
|||
|
|||
Traffic Loop Sensor Trigger For Bikes
In article
, " wrote: On Nov 10, 3:01*pm, " wrote: On Nov 10, 4:44*pm, Michael Press wrote: " wrote: It need not be steel, only a conductive body that will have eddy currents induced in it by the inductive loop in the pavement. I take it that aluminum is far less conductive than steel then? *I know from experience of several of these sensors that my older mostly steel Ninja would trip that the newer mostly aluminum R6 wouldn't. http://www.howstuffworks.com/question234.htm Aluminum is a very good conductor. The issue here is the inductance. Placing the metal object near the wire loop changes the inductance of the loop. The control circuit is monitoring the inductance by sending an AC current through the loop and effectively measuring the time constant. The metal bike acts like the ferrous core that one puts inside a loop of wire to make a useful inductor as an electrical component. Aluminum also increases the inductance, but not as effectively as iron because it has a much lower magnetic permeability than iron. http://en.wikipedia.org/wiki/Inductor http://en.wikipedia.org/wiki/Magnetic_permeability Traffic loop sensors run a 20000 Hz or more. A conducting body near the loop makes the combined system a different circuit. The varying magnetic field of the loop induces currents in a nearby conductor that reduce the inductance of the combined circuit, raising the resonant frequency of the combined circuit. Note however that a ferromagnetic effect will _increase_ the inductance of the loop, increasing the resonant frequency and evading detection by the signal detection system. The ferromagnetic effect of the steel in a car is overwelmed by the large silhouette of the conducting body, so the overall effect is reduction of the overall induction. -- Michael Press |
#27
|
|||
|
|||
Traffic Loop Sensor Trigger For Bikes
In article ,
Mike Rocket J Squirrel wrote: From the "More Stuff on a Bicycle Is Better," Dept. http://gizmodo.com/5079430/traffic-l...e-green-lights Al bicycle rims lend themselves well to detection by inductive loop detectors because they provide an excellent conductive loop and are located close to the ground where the loop wires are. Here is what to do. Find a section of the sensor loop that is parallel to your direction of travel an put your wheels directly above that section with the bicycle straight up. This maximizes the induction in the rims. -- Michael Press |
#28
|
|||
|
|||
Traffic Loop Sensor Trigger For Bikes
On Nov 12, 4:30*pm, Michael Press wrote:
In article , *Mike Rocket J Squirrel wrote: *From the "More Stuff on a Bicycle Is Better," Dept. http://gizmodo.com/5079430/traffic-l...for-bikes-gets... Al bicycle rims lend themselves well to detection by inductive loop detectors because they provide an excellent conductive loop and are located close to the ground where the loop wires are. Here is what to do. Find a section of the sensor loop that is parallel to your direction of travel an put your wheels directly above that section with the bicycle straight up. This maximizes the induction in the rims. That definitely helps, but it's not 100% reliable. If the sensitivity is set too low, it won't trip the light. In that case, if the coil is rectangular, tipping the bike down toward the inside of the rectangle (tires placed as before) sometimes does the trick. Sometimes they put a figure 8 coil down to help cyclists. It shows up as a double rectangle, i.e. three parallel lines in the direction of travel, boxed in by perpendicular lines fore and aft. IME, these work well only if the bike is on the center parallel line. Aligning over the outside parallel lines doesn't work. This is because the field is tightly contained between the two rectangles. I know this is all on a website somewhere. I'll google later, if nobody else has. - Frank Krygowski |
#29
|
|||
|
|||
Traffic Loop Sensor Trigger For Bikes
In article
, Frank Krygowski wrote: On Nov 12, 4:30*pm, Michael Press wrote: In article , *Mike Rocket J Squirrel wrote: *From the "More Stuff on a Bicycle Is Better," Dept. http://gizmodo.com/5079430/traffic-l...for-bikes-gets... Al bicycle rims lend themselves well to detection by inductive loop detectors because they provide an excellent conductive loop and are located close to the ground where the loop wires are. Here is what to do. Find a section of the sensor loop that is parallel to your direction of travel an put your wheels directly above that section with the bicycle straight up. This maximizes the induction in the rims. That definitely helps, but it's not 100% reliable. If the sensitivity is set too low, it won't trip the light. In that case, if the coil is rectangular, tipping the bike down toward the inside of the rectangle (tires placed as before) sometimes does the trick. Sometimes they put a figure 8 coil down to help cyclists. It shows up as a double rectangle, i.e. three parallel lines in the direction of travel, boxed in by perpendicular lines fore and aft. IME, these work well only if the bike is on the center parallel line. Aligning over the outside parallel lines doesn't work. This is because the field is tightly contained between the two rectangles. The figure 8 is a quadrupole loop, an improvement over the dipole loop. I know this is all on a website somewhere. I'll google later, if nobody else has. http://www.humantransport.org/bicycledriving/library/signals/green.htm -- Michael Press |
#30
|
|||
|
|||
Traffic Loop Sensor Trigger For Bikes
Patrick Lamb wrote:
Is there a single common frequency that all these things use? I've toyed with the idea of building a light weight circuit with a small antenna to disrupt the flux, but I don't care enough to build much smarts into the system. Pat I was told by someone with the highway dept that there is not a single frequency. All the loops at any one intersection are from 20Khz to 60Khz, because if any two shared the same frequency, they would suffer from RF cross-talk inside the control box where the wiring converges. So each one is adjusted different and randomly, and there are no guidelines except for the street dept to change a frequency any time that a nearby business reports a problem near a frequency that the traffic loops were set to. The actual frequency adjusters are unmarked or only rough-marked, so the crews don't normally know exactly what frequencies are in use--they only need to know to set each loop at any intersection different from any others. You could (I would guess) build a "sweeping" oscillator, that would go from the lower limit through to the upper limit, at the press of a button. That wouldn't require active detection. I don't know how much time the sensor has to detect before it triggers the light, however.... ~ |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
bikes are too fast for sidewalks, and too slow for traffic lanes | KingOfTheApes | General | 34 | July 23rd 08 04:20 PM |
bikes are too fast for sidewalks, and too slow for traffic lanes | KingOfTheApes | Rides | 24 | July 23rd 08 04:20 PM |
Bicycles, Traffic Signals, Loop Detectors -- rules where you ride? | No Name | Techniques | 27 | March 21st 07 10:38 PM |
A bit OT, but it is bikes/NYC traffic/rock music | Ted Bennett | Techniques | 48 | December 17th 05 03:18 AM |
Trade new Polar S2 speed sensor \ transmitter for cadence sensor | Chris M | Techniques | 0 | November 10th 05 07:11 PM |