What sort of signal is the knock sensor?

[Don.F.Broadus at ucm.com]

I 'm using a 1.5 inch threaded pipe (1/4 inch NPT)  I removed the pipe and
butted the  sensors together. This did not provide enough coupling to
trigger the ESC. I don't have any more NPT pipe so  I then filled the pipe
with ultrasonic coupling fluid to see if the cavity was resonating. 6KHz was
still the sweet spot although a little quieter now.  I believe each det
sensor being a peizo transducer has been tuned like a quartz crystal at a
certain freq. (6KHZ)  By using two  DR 562 sensors they both are in
resonance at 6 KHZ. I need to find more det sensors as I only have one of
certain types right now. The DR 562 is by far the easiest to find being used
on V8's , V6's four's carbed and injected. I'm looking for Quad  4 sensors
to test believing that they will be tuned  higher to mask the bucket tappets
and chain noise.
                                                 Don  

> -----Original Message-----
> From:	jsg at donet.com [SMTP:jsg at donet.com]
> Sent:	Tuesday, November 23, 1999 3:59 PM
> To:	gmecm at efi332.eng.ohio-state.edu
> Subject:	Re: What sort of signal is the knock sensor? 
> 
> | By using the output of a HP3324A function generator connected to  DR 562
> | knock sensor coupled with a 1/4 pipe to another DR 562 knock sensor I
> was
> | able to track the freq. curve of the sensor. The sensor responds to
> 
> <delete>
> 
> | with a scope the DR 562 sweet spot was 6KHZ. A loud tone could be heard
> at
> | 6KHZ indicating resonance.  7-10KHZ had good outputs. The voltage
> dropped
> | off at 12 KHZ . An output was observed up to 50KHZ very small amplitude
> 4
> 
> Don, is this a resonance of your test setup or of the sensor? (i.e.,
> if you double or halve the length of pipe, does it stay the same?)
> 
> john gwynne