knock sensing

reliant_turbo · Post by **reliant_turbo** » Thu Jun 01, 2006 1:21 pm

Boris740 wrote: KnocksenseMS comes tuned to have maximum sensitivity to knock frequency for your particular cylinder bore. Your original sensor that comes with the car should work fine. Some sensors (Bosch) have flat frequency response in which case KnocksenseMS does all the filtering while others are resonate type meaning that they have maximum sensitivity to the knock signal for that specific bore that they were deigned for. These sensors will work well with KnocksenseMS as long as they are from that original block. There is no tuning by the user. All you have to do is adjust the threshold level so that it trips on a knock signal and not on the background noise.

Hey Boris, I assume that if I were to send you the frequency range of the knock (as measured by a spectrum analyzer) you could tune the bandpass filtering to match? Im just planning for the future. Thanks.

Brian

Boris740 · Post by **Boris740** » Thu Jun 01, 2006 5:06 pm

reliant_turbo wrote:
Boris740 wrote: KnocksenseMS comes tuned to have maximum sensitivity to knock frequency for your particular cylinder bore. Your original sensor that comes with the car should work fine. Some sensors (Bosch) have flat frequency response in which case KnocksenseMS does all the filtering while others are resonate type meaning that they have maximum sensitivity to the knock signal for that specific bore that they were deigned for. These sensors will work well with KnocksenseMS as long as they are from that original block. There is no tuning by the user. All you have to do is adjust the threshold level so that it trips on a knock signal and not on the background noise.
Hey Boris, I assume that if I were to send you the frequency range of the knock (as measured by a spectrum analyzer) you could tune the bandpass filtering to match? Im just planning for the future. Thanks.

Brian

I can set up the KnocksenseMS bandpass filter to be centered on your specified frequency.

reliant_turbo · Post by **reliant_turbo** » Mon Jun 05, 2006 6:41 pm

thats what I figured. Thanks.

now here is the new task that I have to get figured out... how I want to measure the knock to get the exact frequency. I know that I can easily bolt a bosch sensor to my engine where I plan to mount it in the end and then free rev the engine to 3-4krpms and advance the timing till I get some pinging. It wont be under heavy load/boost/etc so it should be fine. I plan on using my beater PC sound card running audacity or something similar to measure/record the knock signal and perform FFT so that I can narrow down the frequency. I have a scanner and a detonation tube ( metal tube clamped to engine with a hose into the engine bay into a set of hearing protectors... works great!

) to make sure Im getting knock at a lesser level than ill hear with my ears so there is no threat of damage...

what I need is just a little guidance on how the bosch sensor works so that I can hook it up to a line level input on a sound card to measure/record. do you feed a voltage into the sensor and the output goes to the input of the sound card through a certain resistance so that it doesnt overload?

heres what in envision....

to GND on beater PC sound card<------ -[BATTERY/REGULATED POWER SOURCE]+ -----> to sensor ----[SENSOR]---- ---->To +[LINE_IN]- -----> to GND on beater PC sound card

the "-" and the "+" on the BATTERY/REGULATED POWER SOURCE and the LINE_IN are just to show polarity.

any insight? thanks

Brian

FiatFreak · Post by **FiatFreak** » Tue Jun 06, 2006 3:11 am

I believe the knock sensor are piezoelectric devices and do not require a power source. They will give off an AC signal that will probably have to be amplified for your sound card to pick it up. But, it would be worth a try to just connect it directly. The polarity of the sensor does not matter, just hook up the two wires as a microphone input to your sound card. Let us know the results!

Boris740 · Post by **Boris740** » Tue Jun 06, 2006 5:19 am

All true. Here are couple of links thet have FFT software.
http://www.sigview.com/
http://www.qsl.net/dl4yhf/spectra1.html

johnc32779 · Post by **johnc32779** » Tue Jun 06, 2006 5:42 am

Generally, where on the engine should a Bosch knock sensor be mounted? I assume one would use an existing mount point.

In my case, the engine is a BMW 3.5 liter inline 6 cylinder DOHC 2 valves per cylinder.

Boris740 · Post by **Boris740** » Tue Jun 06, 2006 8:32 am

johnc32779 wrote:Generally, where on the engine should a Bosch knock sensor be mounted? I assume one would use an existing mount point.

In my case, the engine is a BMW 3.5 liter inline 6 cylinder DOHC 2 valves per cylinder.

Existing mounting point would be best. Centered somewhere on the uppermost part of the intake side of the block is the usual spot. Torque to 8-10 ft-lb

maddios · Post by **maddios** » Tue Jun 06, 2006 4:38 pm

which engine? s38? m88?

reliant_turbo · Post by **reliant_turbo** » Wed Jun 07, 2006 6:29 pm

Boris740 wrote:All true. Here are couple of links thet have FFT software.
http://www.sigview.com/
http://www.qsl.net/dl4yhf/spectra1.html

so the bosch one doesnt require power then? cool! I'll have to get one and start experimenting with it. I know for the dodge knock sensor on the 2.2L/2.5L turbo cars, the knock voltage gets up to 4V+ if its really knocking bad above 4000rpms. The sensor is similar to the GM narrowband ones so thats why I want to switch to a flat freq one if and when I go to megasquirt.

thanks

Brian