If you have wondered how reverse parking sensors work,
you are not alone. These little technological marvels allow you to back your
vehicle out of a driveway or parking space with more confidence and make
driving in reverse safer in general. They detect objects in your vehicle's path
and emit a sound or beep that lets you know you need to stop and check behind
you before proceeding. And, like most technology, it is much easier to add a
sensor to your car or troubleshoot and repair one if you know what you're
getting into.
How They Work
Parking sensors are labelled by various vehicle manufacturers under many
different brand names, such as Park Distance Control, Park Assist, Parktronic,
or EPS, but they only come in two varieties: ultrasonic and electromagnetic.
Ultrasonic Sensors
These types emit radio or ultrasonic waves that bounce off of objects
behind the vehicle, much like some animals use echolocation. The returning
waves are then registered and analyzed by a computer inside your vehicle. By
measuring the time it took the wave to return to the sensor as well as any
changes in the length or spectrum of the wave, the computer can determine the
size and relative proximity of the object behind you. If the wave returns
quickly, then the computer knows that something is close behind the vehicle and
emits an alarm signal. Most computers and sensors are actually set up to not
register signals that indicate an object is more than a certain distance away
(usually five to 15 meters depending on the way the system is set up).
Since this system relies on the use of
sound waves, there are cases when the sensor cannot properly detect objects
behind you. For example, some surface types can interfere with how sound waves
reflect, or, if an object is too narrow or small to reflect sound waves, your
sensor will not see it. Also, since an ultrasonic system works by using four to
six individual sensors mounted on the
outside of the car's bumper, there are cases in which blind spots and excess dirt and grimeon the sensors themselves will
contribute to a lack of detection.
Electromagnetic Sensors
As indicated by the name, these sensors operate using electromagnetic
waves. A transceiver strip generates an elliptical near field behind the car,
and hen objects that meet a certain mass requirement disturb that field, a
detector picks up the voltage change and sends the information to a computer in
the car. The computer analyzes the data to determine the distance to the object
and then alerts the driver with a series of tones that grow progressively
louder or faster as their vehicle gets closer to whatever is behind it.
Most, if not all, of these sensors mount on the inside of
your vehicle's bumper, so there is no issue with dirt interfering with the
system's detection capability. These are also the more discreet design;
however, they may prove to be a more complicated install for some DIYers.
Detecting Moving Objects
Some parking sensors can detect moving
objects as well, but they will react in much the same fashion regardless. In
the case of an ultrasonic system, once a sensor receives a signal or wave that
the computer determines is close, all sensors on the rear of the vehicle will
then send a signal or wave simultaneously. Depending on which sensor receives
the returned wave, the computer can determine if the object is moving or not.
However, the system will still sound the alarm the entire time the object is
within the sensory area.
Electromagnetic sensors will also
register a moving obstruction in the same manner as a non-moving one if it's
close enough. These sensors actually only react to objects approaching the
bumper, so fixed accessories like tow bars don't perpetually set off the alarm,
so a moving object, like a person, will set off the alarm until it leaves the
field if it is in close enough proximity.
