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We have a bunch of trucks in the workplace that drive inside the premises. I want to calculate their exact running time. Currently, we can capture engine hour data by tapping the signal of the alternator.

But what if the engines are left ON while the truck is standing? My new idea is to detect if the wheels are also rotating or not. I have read that wheel speed sensors can sense the speed of moving vehicles. Can these sensors be an answer to the problem at hand? Can I tap their signal too?

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Yes, the wheel speed sensors can detect if the vehicle (or at least the specific wheel the sensor is tied to) is moving. On most vehicles you should be able to tie directly into the wheel speed sensor and detect the signal, while not causing any issues with the vehicle itself while in normal operation.

The sensor itself is a standard sine wave orientation. It's either on or off and is predictable. If there is movement in the signal, there is movement in the wheel sensor and movement of the wheel which is attached to it. Depending on how old the vehicle is, it could be a two or three wire speed sensor. I believe both of them work basically the same, but the three wire sensor is going to be more accurate. It uses what is called the Hall Effect, where you have vehicle voltage as the base reading (using two of the wires), then the third wire picks up the signal. On the other side of the equation is the stator which has equidistance notches in it which pass by the sensor and causes the signal. In order to use it, you just need to figure out which is the signal wire and then tie into it to get the signal. If you have a device which can detect the Hz which is produced, you can calibrate against the speedometer or GPS device to figure out how fast the vehicle is moving.

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A data logger will record all or most of your 'sensors' for you to examine at leisure. For a vehicle with a standard sixteen pin DLC, something like the Launch CRecorder or similar, but check for compatability to your vehciles.

  • The ECU is programmed to report a mileage in mainly two ways. The vehciles speed sensor will report a speed of vehicle based on the number of times the gearbox turns for any particular tyre size. The brakes ABS sensor will report a vehicle speed from the wheel its operating on again relative to tyre size. The data logger is transferable from vehicle to vehicle with no re-wiring or fuss and is very cheap to buy. – Allan Osborne Jul 26 '14 at 11:39

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