Listening to corona discharge with ultrasound - Page 1
Forum section: electronics / projects

author: 123lollipop
author_rank: Newbie
timestamp: March 20, 2017, 09:17:37 am
content: Hi,I have a student project where I'm listening to corona discharge in the ultrasonic region. I have my test set-up rigged up and ready to go, but having problem with my ultrasound sensors. I have different transducers, but I get none of them to work properly. I have read enough papers to know that it should do the job, but when it comes to the schematics I'm a bit more confused and tangled how the sensors work. Here's a link to the datasheets of the sensor I'm trying to make work:http://no.mouser.com/ProductDetail/Kobitone/255-400ST16-ROX/?qs=RgIboipJs7eu6F5NaOfjjg%3D%3Dhttp://www.murata.com/en-us/api/pdfdownloadapi?cate=&partno=MA300D1-1Hope anyone can help me realising this project. Thanks!Erik

author: DTJ
author_rank: Super Contributor
timestamp: March 20, 2017, 10:04:07 am
content: I'm no ultrasonic expert, far from it, but perhaps you need to provide more information on what it is you are trying to do.The sensor data sheet is for a 300khz part. I think the sensitivity bandwidth will be very narrow.Will it be sensitive enough?What frequencies are you expecting to see?How well and how far will a 300khz wave travel in air (which I assume is your medium)?Perhaps use a second transducer as a source to test your receiver.

author: Zero999
author_rank: Super Contributor
timestamp: March 20, 2017, 11:12:21 am
content: Quote from: 123lollipop on March 20, 2017, 09:17:37 amAre any of those papers freely available? If so, please post links. Otherwise, can you provide a summary?

author: 123lollipop
author_rank: Newbie
timestamp: March 20, 2017, 12:12:30 pm
content: Quote from: DTJ on March 20, 2017, 10:04:07 amYou might have a point when it comes to the narrow bandwidth and the traveling distance of the wave, so you might have a point there. We get some output from it, but that's in the very low KHz range, so it might pick up the popping sound. Also in the megahertz range but that is electromagnetic noise I guess. It was a long shot for that one to work, but I will try to set up a second transducer to test the reciever

author: 123lollipop
author_rank: Newbie
timestamp: March 20, 2017, 01:26:53 pm
content: Quote from: Hero999 on March 20, 2017, 11:12:21 amMost of the papers are IEEE papers, so if you don't have access to papers there I'll try to give you a quick summary.In transformer stations ultrasound detectors with center frequency of 40KHz is often used to detect corona discharge in transformer insulation. There is some newer papers that suggest that one can find corona discharge in the spectrum og 20KHz-350KHz, though there are different opinions on the bandwith useable for corona discharge detection.My main question in terms of this is that I'm not sure if I have to drive the sensors or if the would work sensor -> pre-amp -> oscilloscope (or MCU later).Here's just one of the ultrasound corona discharge detectors:https://www.checkline.com/product/MK-720

author: SeanB
author_rank: Super Contributor
timestamp: March 20, 2017, 02:02:04 pm
content: How about buying a cheap piezo tweeter ( not the ones with an integrated transformer, just the piezo only horn type) and use a band pass filter on the output to limit the signal from handling ( or just a semi decent high pass one passing all over 30kHz as a beginning) and then some amplification to get a lab response to a spark from a lighter being lit ( obviously one with a piezo striker) across the room. Should give a good idea of the bandwidth you need and the signal levels out of a cheap piezo speaker.

author: Audioguru
author_rank: Super Contributor
timestamp: March 20, 2017, 04:31:04 pm
content: The 40kHz ultrasonic transducers from Mouser pickup only frequencies near 40kHz as shown on the datasheet. The receiver transducer output will need a preamp with a fair amount of gain.What do you feed the from output of the preamp? An oscilloscope? You will not hear anything. An electronic circuit can be used to downshift the frequency so it can be heard as a crackling tone.

author: 123lollipop
author_rank: Newbie
timestamp: March 20, 2017, 06:24:19 pm
content: Quote from: Audioguru on March 20, 2017, 04:31:04 pmWhy won't I see anything of the oscilloscope?

author: Audioguru
author_rank: Super Contributor
timestamp: March 20, 2017, 06:35:17 pm
content: Quote from: 123lollipop on March 20, 2017, 06:24:19 pmI said you will not hear anything at the output of the preamp. An oscilloscope will show the 40kHz signal at the output of the preamp jumping up and down, because the transducer resonates at 40kHz.

author: 123lollipop
author_rank: Newbie
timestamp: March 20, 2017, 06:41:25 pm
content: The preamp may be bad wording from meWhat I want is the signal on the scope. If I wanted to listen to it I could use CD4024 to get it in the hearing range. The problem I'm having is that I'm not even getting anything on the scope either..

author: mark03
author_rank: Frequent Contributor
timestamp: March 27, 2017, 01:15:59 am
content: Decades ago I built an "ultrasonic receiver" based on a how-to article in Radio Electronics, Popular Electronics, or some similar magazine which were popular at the time. The impetus for the author was pinpointing the RFI-causing corona discharge on the public utility poles in his neighborhood. He used a hifi piezo tweeter from Radio Shack and a circuit based on the 4066 quad CMOS switch. It worked fairly well, although ultrasonic "interference" from my fingers running over the enclosure, and turning the tuning knob, was a problem. Jangling keys make lots of ultrasound to test with. Also any CRTs, if you still have any nearby.For corona discharge, remember that sound attenuation in air rises *very* steeply with increasing frequency. You want to stay as close to the audible range as feasible given the source spectrum. Thus, I think the piezo tweeter suggestion is a good one.I'm currently re-doing the same project using analog MEMS microphones bandpass filtered from ~ 20-100 kHz, with the demodulation performed in DSP (STM32L4). Knowles has one or two modules which are explicitly profiled for ultrasonic response, although AFAICT this is incidental and most analog MEMS mics would have similar performance. Possibly an option if you're having a PCB made and aren't afraid of SMT prototyping.