Oscilloscope= analyse piezo - Page 1
Forum section: electronics / testgear

author: harps
author_rank: Regular Contributor
timestamp: July 24, 2018, 02:14:28 am
content: hello thereI am looking to buy a cheap digital Oscilloscope to analyse a piezo element output . So i can capture a short signal,clearly see the waveform shape so to measure its output (and dynamic range)i could buy a bit more expensive and sell afterwards, but I would rather buy a cheap scope.Please can someone advise a model? Would a pc based Hantek be o.k just for this type of measurement?thank you : )

author: joeqsmith
author_rank: Super Contributor
timestamp: July 24, 2018, 02:56:35 am
content: Quote from: harps on July 24, 2018, 02:14:28 amAny idea of the what the waveform looks like? Maybe what sort of device it is?I use a grill ignitor for ESD testing which uses a piezo. If you are looking at something like this, the following video may be of interest.https://youtu.be/Qimtx8z6FUQ

author: harps
author_rank: Regular Contributor
timestamp: July 24, 2018, 03:09:17 am
content: hellothey are approx 2cm piezo discs /elements and i hope to look at the waveforms they output.thanks for the video linkI just wonder what features I would need in a scope to measure them, like single shot trigger and so forth.and if a cheap scope would be good enough?

author: joeqsmith
author_rank: Super Contributor
timestamp: July 24, 2018, 04:20:12 am
content: Hard to say without knowing how you plan to use them. Maybe just post your test plan or setup. If you watch that video, when that striker hits the piezo in the grill igniter, the pulse width is 5ns. I show some of those pulses having sub 1ns rise times.

author: harps
author_rank: Regular Contributor
timestamp: July 24, 2018, 07:00:11 am
content: I am just learning and experimenting at the moment, I might make a percussive instrument as a project. I am not sure yet.From that video I gather a 5ns per division should good enough to see a waveform.

author: Fungus
author_rank: Super Contributor
timestamp: July 24, 2018, 10:33:56 am
content: Quote from: harps on July 24, 2018, 07:00:11 amI've played with piezo discs before. You don't need much of an oscilloscope to see the output.Last time I did it I was in a bar and using one of these:https://www.ebay.com/sch/i.html?_nkw=dso+quadThose only have a bandwidth of about 10MHz. Any DSO or analog oscilloscope you can find will be better than that.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: July 24, 2018, 11:58:58 am
content: You could use a cheap multi meter, analogue would be better. As to your question, how much money are you looking to spend. If not alot get a DSO 138 on ebay for 20 usd, it should be more than adaquate. You could use it in one shot mode.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 24, 2018, 12:25:35 pm
content: How fast the pulses, edges are depends on the size of the piezo and thus it's mechanical resonances. So a 2 cm disc one is more like a slow one of maybe a few kHz, maybe 10s of kHz in thickness mode. Those super fast edge pulses are more due to arcing caused by high voltage.For just a crude first view, a simple sound-card interface (e.g. 2 diodes for protection) could do it.

author: Fungus
author_rank: Super Contributor
timestamp: July 24, 2018, 01:32:31 pm
content: Quote from: joseph nicholas on July 24, 2018, 11:58:58 amYou're not going to see a 1ms pulse on an analogue meter (and probably not a digital meter either).Quote from: joseph nicholas on July 24, 2018, 11:58:58 amYep. I imagine a DSO 138 could show the pulse prom a piezo disc. IIRC the pulses I saw were in the ms range.

author: StillTrying
author_rank: Super Contributor
timestamp: July 24, 2018, 01:48:14 pm
content: You could get some sort of cheap results usingwww.zeitnitz.eu/scope_enI'd use 4 914 diodes, 2 in series back to back, the clipping at +1V and -1V would give a rough voltage calibration.

author: Fungus
author_rank: Super Contributor
timestamp: July 24, 2018, 03:13:24 pm
content: Quote from: StillTrying on July 24, 2018, 01:48:14 pmNope, a diode won't tell you much about the voltage at all.A piezo disc fires out a bunch of electrons when you hit it, a bit like an inductive pulse so the voltage you see/measure will depend almost 100% on the impedance of the measurement device.A diode will swallow up all the electrons from a piezo as soon as it reaches its breakdown voltage so you'll only see 0.7V (or so).This could give a false sense of security - you might get amuchhigher voltage in the final device if it has a high impedance.

author: StillTrying
author_rank: Super Contributor
timestamp: July 24, 2018, 10:08:59 pm
content: I meant calibrate the SoundCardOsc's Y sensitivity to +1V at the top and -1V at the bottom of its screen, if it makes any difference!I've tried it as an experiment. I must have been using the mic input because the SCO flat topped at only +/-0.5V, - long before the 4 diodes would conduct, so I decided to just tap the 35mm piezo very gently to keep it's output below 1Vpp and get some results. It was easy to get plenty of good captures.For proper finger taps I think you'd need to use a 20:1 potential divider, and for hitting the piezo with wooden sticks 200:1.