Best method for finding shorts?? AC or DC current injection, TIC??? - Page 1
Forum section: electronics / projects

author: dazz1
author_rank: Frequent Contributor
timestamp: March 18, 2022, 07:33:34 am
content: HiI used to think the only useful method of finding shorts was current injection to trace the DC voltage drop until it was near zero at the short, using Kelvin probes.Then I discovered hideously expensive, but high resolution, thermal imaging cameras (TIC).Most recently I read about low current, low frequency (100Hz to 1000Hz) current injection using a coil to detect and trace the path of the current to the short.Is there another way?What is the best way?

author: IanJ
author_rank: Unknown
timestamp: March 18, 2022, 07:42:53 am
content: I use three methods and will jump between them depending on the board and just for variety/luck.1. Flir C2 thermal camera. Modified so its thermal overlay is good at 6" distance.2. Use a 6.5digit bench DMM and test the resistance across parts around the pcb. The lowest value indicating i'm closest to the short.3. Calibrated engineers finger.Ian.

author: kripton2035
author_rank: Super Contributor
timestamp: March 18, 2022, 08:14:21 am
content: see my shorty-with-display for a low cost DIY solution.http://kripton2035.free.fr/Projects/shorty-display.htmlit depends on what short you search for.if it is a shorted capacitor, an AC injection will give you all capacitors of the board, so a DC injection is needed hereif it is another type of short, an AC injection can be used.

author: dazz1
author_rank: Frequent Contributor
timestamp: March 18, 2022, 09:29:36 am
content: Quote from: kripton2035 on March 18, 2022, 08:14:21 amI like that.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 18, 2022, 09:48:51 am
content: The mohms meter with still only a single tip is tricky. Separate contacts for the votlage and current and thus proper 4 wire measurement can help quite a bit. So the preferred method is with separate wires for the current injetion and reading the voltage. With a lab supply for the current it would need a relative sensitive (e.g. 10 µV or better resolution) voltmeter. So one may not need a special instrument for this.There are different type of a short:1) a near perfect short. This is not very well seen with a thermal camera, as there is little heat and the supply lines may show up instead of the actual short. On the positive side a near dead short means low voltage and than the AC injection method is not effected much by capacitors. DC resistance is also working OK as not mich current goes other ways.2) a not full short, with still quite some resistance, maybe even still a PN drop. This case would be easy to find with the thermal method (camera, parafin smoke, finger), but capacitors can interfere with the AC injection method.If really needed the AC injection method could be build to separate capacitor current from resistive current by the phase shift.

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 18, 2022, 10:51:59 am
content: Quote from: kripton2035 on March 18, 2022, 08:14:21 amHey, great projectI really miss those old-shool sites, was the nice internet era.Really nicely done.I guess you made a lot of testing when you made it, but just let me askWas wondering if the battery life could be improved by lowering the injection current and increasing the op-amp gain.82ohm load will draw 60ma from the 5v rail, these 9V batteries won't last very long.Cheers!

author: kripton2035
author_rank: Super Contributor
timestamp: March 18, 2022, 11:46:34 am
content: Quote from: DavidAlfa on March 18, 2022, 10:51:59 amthanks !I use 9v li-ion batteries, and as you may know, I tested it again and again and again...and frankly the battery last some months without recharging, it's enough for me I did not search to lower the consumption.in the shorty simulation, the analog part draws some 37mA max. (need to add the arduino and the display)

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 18, 2022, 12:18:06 pm
content: Shorty is clever. They also sell liquid crystal sheets that change color at different temperatures. Sometimes you can lay this on a circuit board to see temperature differences. There's also the smoke method. Turn up the current and see what smokes!

author: Shock
author_rank: Super Contributor
timestamp: March 18, 2022, 02:07:13 pm
content: Two easiest would be milliohm meter and a thermal camera. Two cheapest would be multimeter voltage drop and ipa evaporation as most people have those anyway. Two most risky is pokey finger and no current limit.