Parking sensors

The purpose of this test is to evaluate the operation of ultrasonic proximity sensors (referred to as parking sensors) using an Ultrasonic parking sensor detector.

How to perform the test

View connection guidance notes.

1. Connect the Ultrasonic parking sensor detector to PicoScope Channel A.
2. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
3. Start the scope to see live data.
4. Activate the vehicle's parking sensors (refer to the owner's manual). Assistance may be required to ensure personal safety (see Notes).
5. Hold the Ultrasonic parking sensor detector around 25 mm from the parking sensor surface.
6. While aiming the Ultrasonic parking sensor detector directly at the parking sensor, manoeuvre it in a circular fashion to obtain the best possible signal.
7. With your waveforms on screen stop the scope.
8. Restore the vehicle to a safe rest position (engine off).
9. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Notes

You may need to have the transmission in reverse or a forward gear with the engine running (and the clutch disengaged) to activate the parking sensor system. If so, a qualified driver must be in control of the vehicle at all times. Therefore, you will need two operatives, one to control the vehicle and one to take measurements, during testing of the parking sensor system.

Example waveform

Waveform notes

This known good waveform has the following characteristics:

• An oscillating pulse that almost immediately builds up to its highest peak to peak amplitude and then decays over a longer time period.
• The overall size of the pulse depends on the proximity of the Ultrasonic parking sensor detector to the parking sensor and the serviceability of the sensor.
• Generally, when the Ultrasonic parking sensor detector is held at the same distance, the pulse amplitudes should be the same for every sensor. However, there may be some deviations from vehicle front to back or inner to the outer (about the vehicle center line).
• The pulse oscillation is around 40 kHz.

Further guidance

A typical parking sensor can be considered as both a transmitter and a receiver. An internal piezoelectric device is utilised to not only generate a high-frequency pulse through the air but also to convert any reflected pulses to a voltage representation of distance.

The parking sensor is initially driven by the relevant onboard vehicle computer for sufficient time to excite the piezoelectric element at high frequency (around 40 kHz). This excitement results in a pressure pulse being emitted from the surface of the parking sensor. The pressure pulse produces an inaudible sound wave (it oscillates at a frequency beyond the range of human hearing).

The time taken to excite the parking sensor (computer controlled) is critical as the piezoelectric element is required to resonate at 40 kHz almost instantaneously, then return to rest and await any reflections. The return to rest takes time; this decay time is referred to as ringing and represents the dissipation of the sound energy generated by the piezoelectric element.

During the ringing, the onboard computer will pause before listening to any reflections received by the parking sensor. Otherwise, the ringing could interfere and disguise any reflected pressure waves.

When the sound waves leave the surface of the parking sensor, the time taken for the piezoelectric element to receive any reflected sound waves determines the distance between the parking sensor and reflecting object.

The correct operation of parking sensors is dependent upon their position/orientation (aftermarket fitment), wiring harness connectivity, surface contamination or degradation, control unit functionality, and their operational environment being removed from sources of intense telecommunication and ultrasonic activity.

Whilst holding the Ultrasonic parking sensor detector at the same distance and location from each of the vehicle’s parking sensors in turn, compare the amplitudes of measured pulses to identify inoperative sensors or those that are producing a diminished output.

GT814-EN