Vehicle Speed Sensor

It has happened to the great majority of us. We are cruising along, perhaps its summer and the windows are down, we are listening to our favorite song and life is good, then uh oh, blue lights. Is there anything worse than that sinking feeling you get when you realize that the police officer behind you is motioning for you – yes, YOU – to pull over and take your medicine all because you forgot to watch your speed for a few minutes.

Sometimes these routine stops can get a little tricky. Perhaps you were watching your speed and feel that you were complying with the speed limit while the nice police officer with the radar gun thinks otherwise. Perhaps you are both right – you truly thought you were in compliance with stated speed laws and the officer clocked you going above them. If your vehicle has a faulty vehicle speed sensor (sometimes called a VSS), then this sticky situation could indeed happen to you.

So what is a vehicle speed sensor? A vehicle speed sensor is a device used for reading the speed of a vehicle by calculating its wheel rotations. The actual makeup of a vehicle speed sensor usually consists of a piece called a toothed ring and one called a pickup. A vehicle speed sensor is a type of what is known as a tachometer, an instrument that measures revolutions of an object and as sometimes called a rotation counter.

In road vehicles, vehicle speed sensors are used within a car’s anti-lock braking system. But where vehicle speed sensors are most commonly used and needed are in rail vehicles such as locomotives or multiple unit rail vehicles. Rail vehicles require an extremely precise vehicle speed sensor reading because their operation depends quite a bit on the ability to measure speed and changes in speed. Trains and other rail vehicles need traction control and protection from wheel sliding. Vehicle speed sensors dispersed all around the train or other rail vehicle help track speed on what is often a large and complicated piece of machinery.

Have you ever heard the phrase “it’s like watching a train wreck” or perhaps even heard your grandparents or other old folks talk about watching a train wreck? In the past, train wrecks were big events. The carnage was spectacular compared to anything that rural people, the majority of the U.S. population at the time, had ever seen and train wrecks were a cause for speculation in rail towns long after the actual wreck was cleared up and hauled away. Rumor has it that some enterprising souls made postcards out of pictures of train wrecks and sold them to people, who in turn hung them up in their homes as proud trophies.

Why did these train wrecks happen? Perhaps there was a fault in the train’s vehicle speed sensor. Vehicle speed sensors often failed to function at an acceptable safety level and often led to faults such as train wrecks where engineers were unable to stop on time. Of course, this could have been because of the extremely harsh conditions that rail vehicles often encountered back in those days and, as a matter of fact, still do encounter even to this day. Different boards of standards and practices put forth strict standards for railroad safety, including requiring all parts equipment used on trains and other rail vehicles to comply with strict guidelines . Failing to comply often came with harsh penalties (if the guilty party wasn’t found out first when his rail vehicle was subject to a malfunction.) Vehicle speed sensors are vital to the operation of one of the United State’s oldest and most viable transportation system – rail travel.



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