Equipment suggestions please - Page 1
Forum section: electronics / beginners

author: JACIII
author_rank: Newbie
timestamp: November 02, 2013, 11:59:26 am
content: Newbie here. Apologies if this is the wrong section.Hey Y'all, need to do two things to troubleshoot and insure the consistency of a roughly 25 millisecond 130v/125A weld arc. It's a one shot event every three seconds and I am looking at voltage, current, and segments of the arc time (1 millisecond to 50+milliseconds range)1)Have been looking at cheap DSO's and have used a Fluke 199c with a current sensing ring in the past on this, but the Fluke belongs to the company I work for, is scary expensive, I don't have immediate on demand access to it, and it's easy to get lost in the menus.2) need to measure ohms (the welder's internal resistor column) accurately from about 0.5 to 2.0 (No, that's not Kohms or Mohms - just plain ohms)- the flukes I have used are typically all over the place in this range and will give a spread of a couple tenths of an ohm over successive measurements. Have been forced to take ten readings and average and just go with that. Is there a better instrument for this?Thanks for any suggestions,JACIII

author: DL8RI
author_rank: Regular Contributor
timestamp: November 02, 2013, 12:08:04 pm
content: Hi,Quotesuch low resistances should be measured by a 4-Wire-Measurement with kelvin-cleps.Some multimeters have it build in, or you get a extra mOhm-Meter or RCL-Meter.You can get them from cheap to expensive, depending on your budget

author: JACIII
author_rank: Newbie
timestamp: November 02, 2013, 12:12:40 pm
content: Excellent! Hunting a 4-wire-Measurement capable device now!Thankyou!

author: jeremy
author_rank: Super Contributor
timestamp: November 02, 2013, 12:17:27 pm
content: Quote from: JACIII on November 02, 2013, 11:59:26 amCan't really help you with 1, but I occasionally need to measure very small resistances. The standard procedure is to pass a known, fixed and accurate current through the conductor and measure the voltage across it. V=IR -> voila! This is the 4 wire method mentioned by DL8RI, but don't waste your money on a dedicated unit if you're just doing this once or twice. Just get two good multimeters and measure the current and voltage from a PSU. I've done it with two 5.5 digit meters and got very accurate results (I could see tiny temperature fluctuations changing the resistance).Dave and Mike both did videos on this procedure a while back when they were testing if adding extra solder to tracks reduces resistance. Can't find the exact video though sorry.

author: JACIII
author_rank: Newbie
timestamp: November 02, 2013, 12:22:27 pm
content: Will be making the resistance measurement on a regular basis, so there is a new instrument in my future.<sarcasm>I HATE buying more instruments!</sarcasm>That said, I am NOT going out and buying a Fluke 199c......

author: DL8RI
author_rank: Regular Contributor
timestamp: November 02, 2013, 12:47:02 pm
content: Hi,if you're not into new-equipment only, I can recommend the Viedo-Bridges from ESI. Build in the 80s but with a basic accuracy of 0.02% still quite respectable. I have a ESI 2110 and I'm quite happy with it. Of course depends on what you want to do, these instruments are mainly for component-selection and for a normal trouble-shooting a bit of overkill. But if they are calibrated (=you now they are working probably) they make a good lab-standard too.

author: JACIII
author_rank: Newbie
timestamp: November 02, 2013, 01:22:43 pm
content: Sweet! Good used is my preference.Ebay searching now.

author: DL8RI
author_rank: Regular Contributor
timestamp: November 02, 2013, 01:51:23 pm
content: I just did some "measurements" to show the capability of this unit.It has not been warmed up or anything, so don't take the values to serious:This values were repeatable. I got mine in perfect working condition for ~$250, so it didn't cost so much

author: JACIII
author_rank: Newbie
timestamp: November 02, 2013, 08:30:02 pm
content: Yeah,That's a badass piece of equipment.Thanks for the tip.JACIII

author: PaulAm
author_rank: Frequent Contributor
timestamp: November 02, 2013, 08:59:14 pm
content: If you're cheap, not afraid of older equipment and have the bench space, you can find HP 3456A meters pretty cheap. Ohms and volts only, but it will do 4 wire measurements and is a 5.5 digit meter. I've used mine to monitor power consumption of a board by measuring the voltage drop across a fuse (after measuring the resistance). Also includes GPIB if you want to automate measurements.

author: Vgkid
author_rank: Super Contributor
timestamp: November 02, 2013, 11:11:02 pm
content: What about makng your own constant current source, if the resistances will be low.

author: Unknown
author_rank: Unknown
timestamp: November 02, 2013, 11:36:34 pm
content: Quote from: PaulAm on November 02, 2013, 08:59:14 pm6.5 digit. It just defaults to 5.5 digit, but you can switch it to 6.5 digits using 6 STORE NDIGS.

author: JACIII
author_rank: Newbie
timestamp: November 02, 2013, 11:59:16 pm
content: There's one on ebay going for $22.50. Guess who the high bidder is!