Parking Sensor Detector alternative applications

[Steve Smith]

Recent usage of the Pico Ultrasonic Parking sensor detector https://www.picoauto.com/products/test- ... r-detector during parking sensor testing https://www.picoauto.com/library/automo ... g-sensors/ got me thinking about alternative uses for such a device tuned to 40 kHz (Ultrasound)

A number of vehicle alarm systems (O.E and Aftermarket) use such a frequency for interior motion detection and so using the PicoScope Spectrum Mode in conjunction with the Parking sensor detector, it is simply a case of placing the sensor inside the vehicle, arm the alarm system and wait for activity on the scope screen.

Sorry I should have mentioned, PicoScope Spectrum Mode is not “active” by default within the PicoScope Automotive software. Select Tools > Preferences > & Options to access a number of additional, invaluable features of PicoScope.

Set up

Tick the box adjacent to “Spectrum” in order to activate Spectrum mode, followed by Apply > OK Spectrum mode (Frequency based instrument) will now be available for selection at the top left hand corner of your screen.

“Frequency based” means the scope will display frequency along the X Axis rather than Time, and amplitude of the measured signal along the Y Axis. (Identical to our NVH Frequency View)

Frequency Mode

Using the parking sensor detector connected to channel A of PicoScope & placed inside the cabin of our VW T5 van (alarm armed) we can clearly see activity around 40 kHz, confirming our ultrasonic interior motion sensors to be operating. (See above scope screen)

Sensor inside cabin

An interesting bonus using this technique was the ability to monitor “settle time” as the ultrasonic motion sensors do not become active immediately after arming the vehicle. This varies depending on manufacturer but often ultrasonic activation coincides with a change of state from the vehicle Alarm LED. For example: LED reverts to slow flash from fast flash or solid LED to flash etc.

Given we can confirm ultrasonic activity, what about ultrasonic interior coverage?

Using the Reference Waveform feature of PicoScope, https://www.picoauto.com/library/traini ... and-tricks the captured amplitude of the ultrasonic signal in the cabin could be compared to the signal in the load space of our T5 van

Reference waveform

The waveforms above measures the peak amplitude of our 40 kHz ultrasound signal within the cabin (adjacent to the driver) at -89.05 dBu (channel A Blue) and within the upper load space area (adjacent to the rear tail door) at -100.3 dBu (Magenta Reference waveform)

We can therefore conclude the ultrasonic coverage of the load space (whilst protected) the signal strength is much weaker than in the cabin.

This is no surprise given the vehicle ultrasonic transceiver is located within the cabin roof and the design of such interior movement detection may be characteristically biased away from the load space to prevent false alarms from insecure payloads.

Ironically, at the floor level of the vehicle load space there was zero ultrasonic activity detected!
Another reason for pursuing such a measurement was to utilize the vehicles ultrasonic motion sensors for the detection of wind noise.

Using the parking sensor detector on the outside of the vehicle with the alarm system armed (motion sensor active) would enable ultrasound at 40 kHz to be detected around leaking window and aperture seals. (Or so I thought)

Given the ultrasound motion sensors are designed to cover the interior of the vehicle at best, expecting a small aperture/window seal leak (sufficient to generate wind noise) to allow for the passage of ultrasound outside the vehicle was a “big ask”!

I guess with hindsight, this is no bad thing as the number of false alarms from these vehicles would increase tenfold as they age and seals begin to compress over time.

The T5 VW van under test has a known window seal weep sufficient to generate a nuisance wind noise a highway speeds. Using the parking sensor detector with the vehicle alarm system armed confirmed no leakage of ultrasound

Wind noise check

Using a dedicated 40 kHz Squawker placed inside the cabin proved far more effective, delivering pin point ultrasound with sufficient clarity and amplitude to highlight cabin/window seal leakage using the parking sensor detector.

Squawker test

All in all, the above tests conclude the parking sensor detector to have alternative applications where we can confirm alarm ultrasound motion sensor activity, coverage, settle time and leakage (Where large cabin leakages exist. (In reality this would have to be a window left open!)

For detection of wind noise we used a superior dedicated squawker from an aftermarket Wind Noise Leak Detection Kit. These devices can also be obtained from pet stores, electronic suppliers or even “homemade” if time allows

VW T5 INTRUSION SENSOR MID CABIN.psdata

Spectrum Mode capture (Cabin Sensors)

(583.47 KiB) Downloaded 5164 times

I hope this helps, take care……Steve

[scottpitcher22]

Hi steve,
Ive had a number of hvac leaks lately and a number of them have been difficult to find using bubble spray due to hot engine bays or weather conditions. This took me on a path of thinking of other leak detection possibilities, ideally utilising tooling I already owned.

Eventually I got to thinking that if ultrasonic leak detectors are used in hvac leak detection it must be possible to see this on a scope.
My theory took me to find the frequency of the average leak is 40khz the same frequency as the ultrasonic parking sensors operate. Obviously the frequency of the leak is largely proportional to the size of the leak but this is something to play with.

With some playing with the scope using spectrum like in this post I found it is very possible to see a leak. I have only tested this on a very small airline leak so far but have had positive results.

When opening the scope I select a 50mv range and select spectrum view. I found 200-500khz the best view to easily see the leak due to it having a sharper rising and falling edge than that at 100khz which is a much linear rise and fall.

I compared the frequency with a blow gun at different opening rates which showed the average to remain very close to 40khz throughout. I have not tested this against vacuum leaks as yet but expect similar results in theory.

Wondered have you heard of this use before? I’m looking forward to really putting it to the test soon in real world conditions soon.

I have a video of testing but it’s too large to upload.

Regards, Scott.

[Steve Smith]

Hello Scott and thank you for taking the time to experiment and share this technique on the forum

I have carried out similar tests when looking for suspected manifold leaks but without success!

I would like to revisit this test with a deliberate manifold leak in order to determine the sensitivity of our sensor

The results from your blow gun are promising and the Parking Sensor detector will most certainly capture these high inaudible frequencies (40 kHz)

It would be great to hear how your real world tests pan out and how we could improve the parking Sensor detector to further lend itself to such diagnosis

Thank you again Scott, take care.......Steve

[scottpitcher22]

Thanks for your reply,
I had wondered whether a manifold leak would be detectable but I wasn’t sure if any other frequencies would be detected in an engine bay.
I wish I had thought of this at the start of summer to put it to test in real world scenarios sooner but I believe my old work horse clio has a leak so at least this is an option to experiment.

I’ll update with my findings as and when I get the chance to do so

[scottpitcher22]

Today I brought in my clio work horse which I suspected to have a leak or 2. I filled with Nitrogen and bubble sprayed it and found a few leaks in the condenser. One large leak, one small leak and a few really small leaks. Have to say I had great success in detecting these with the parking sensor detector. Every one of them. It was accurate enough to detect the leaks from 6 inches away from the bumper just as strongly as if it was closer to the leak. I’ll be investigating other things I could do to perfect the test, for instance I found it a little awkward looking at the screen and where I was probing. I was wondering if I could add an alarm to spectrum to help focus on where I was proving and an audible warning when a frequency is detected.

[scottpitcher22]

First air conditioning leak today where I tried the parking sensor detector. It was a fair size leak loosing around 1bar every 5 mins or so.
Unable to locate anything using this method or bubble spray until I changed my location of evaporator leak test position. I moved from a single centre vent to footwell vent and changed the position of the vent to match and this is where I found the leak. Although faint. I proved this by changing the vent position turning it back to centre vents and the leak was no longer detectable