Measuring current and Voltage in a PCB Spark Gap - Page 1
Forum section: electronics / beginners

author: marc1996
author_rank: Contributor
timestamp: September 26, 2018, 07:59:21 am
content: Hello,After finishing my simulations of PCB Spark gaps, I have to go to the experimental part, but, I do not know exactly how I should measure the current through the electrodes. About the voltage, I think that I have an idea of how to do it, but, anyway, any tip about how to measuring these characteristics is appreciated.Extra info: I will build a PCB with different models and distances.Thanks,Marc

author: Gyro
author_rank: Super Contributor
timestamp: September 26, 2018, 08:15:36 am
content: For the benefit of other members, the OP's [Edit:otheroriginal] thread...https://www.eevblog.com/forum/projects/simulation-of-the-behaviour-of-a-pcb-spark-gap/

author: marc1996
author_rank: Contributor
timestamp: September 26, 2018, 08:31:23 am
content: Quote from: Gyro on September 26, 2018, 08:15:36 amThank you Gyro,I didn't attach it because I thought maybe there is too much message that is not necessary to answer the question.Marc

author: marc1996
author_rank: Contributor
timestamp: October 02, 2018, 10:20:28 am
content: Could someone help me with this please?

author: Gyro
author_rank: Super Contributor
timestamp: October 02, 2018, 01:14:46 pm
content: I'm not sure how important the current measurement actually is. The spark gap will break down at a certain voltage, which of course is something that you need to measure, but from that point, the current will be determined only by the amount of current that isavailable. For instance, if straight across the mains, then it would immediately develop into a severe arc, limited only by circuit impedance, until a breaker or fuse goes. This is where CAT ratings come in on DMMs etc.The magnitude of the spark or arc will determine the magnitude of PCB destruction - from a slightly increased conductance across the gap, through carbonized and unsafe, though to total destruction.I think you may be able to get more meaningful results by measuring leakage resistance across the spark gaps, before discharge, under various types of contamination, and after discharges of various levels. This is probably more useful information to the manufacturer. There are plenty of cheap high voltage insulation testers available these days that might be helpful.You can probably do a better job bydictatingthe peak discharge current using capacitor(s) slowly charged to known voltage, and using defined high surge current series resistors (and great care for personal safety!). Using the capacitor voltage when the discharge takes place and the series resistor value, you can then accurately determine the discharge current.You might be able to detect a small bias in my attitude towards PCB spark gaps - I think they are the spawn of the deviland a relatively recent 'technical' looking 'fad' which will soon die out again.Please be sure to evaluate spark gaps with routed slots in the PCB too, rather than just different tinned 'electrode' shapes on uninterrupted PCB. Forcing an air gap between the electrodes is the only way I can see of making themrelativelysafe, and mitigate the large change in characteristics after the first discharge due to carbonization of the substrate. Even these need to be evaluated for different degrees of contamination, dust etc.I hope you are able to get some meaningful results to pass on to your sponsor.

author: marc1996
author_rank: Contributor
timestamp: October 03, 2018, 07:20:09 am
content: Quote from: Gyro on October 02, 2018, 01:14:46 pmHello Gyro,Thanks for your response.My doubt about that all the available current will go through the spark gap, do you think that the 100% of it will do it? Because imagine a small X% of it get filtered to the I.C. Depending on the quantity maybe it could damage it.I will apply the IEC 61000-4-2 with an special gun to produce the ESD. The relation between the current and the voltage applying these standards is 3,75A/kV. If I apply 15kV, a current of near 60A will go through it. Imagine If we apply 30kV or something like that. Even a 5% of it would be a high amount of current.But, about the measure of the current, maybe yes it is not that important, but, in order to measure the voltage in the electrodes, do you think a HV tester applied in both conductors is enough?Thanks!MarcEDIT: After thinking for a while I don't think that measuring it with a HV tester is an option, because this will be a nanosecond measure so hardly we will get any result. That was very stupid I think lol

author: licht
author_rank: Newbie
timestamp: November 27, 2018, 09:52:52 pm
content: Measuring current on the ground side is pretty easy with a wideband shunt. T&M Research makes shunt's like this that can be soldered or clamped to a PCB and have a BNC output connector to hook up to your scope. I don't have experience with their smaller shunts but maybe one of SDN series would be good. If your peak current is under a few hundred A you can use a low-value chip resistor with a scope probe across it. Just make sure to use a single ground point for the probe and everything else to avoid bouncing the ground of the scope.You can measure voltage with a high voltage high impedance scope probe. You mention 30 kV so you might need a Tek P6015A but if you can do this at lower voltage I'd go with a PMK PHVhttp://www.pmk.de/en/products/phv_probesseries probe since they're faster and way easier to handle. I use mine with a short spring ground leg instead of an alligator clip to keep the bandwidth high and avoid interference. I think the spring leg thing was included.How'd you end up simulating the spark gap?