IET LOM-501A Micro Ohm meter - Page 1
Forum section: electronics / testgear

author: robrenz
author_rank: Super Contributor
timestamp: March 08, 2012, 06:00:01 am
content: I snatched this from ebay by calling the seller and offering a buy it now price of $350.00 (starting bid was $399.00) he took it. Current starting price from IET is $1975.00 I wanted a meter whose accuracy didn't go to pot below 10 ohms so I could confidently measure contact resistance.Web pagehttp://www.ietlabs.com/lom-510.htmlData sheethttp://www.ietlabs.com/pdf/Datasheets/LOM-510A_530.pdfManualhttp://www.ietlabs.com/pdf/Manuals/LOM-510A_im.pdfIt has 4 measurement modesSwitched DC Mode totally eliminates the effects of thermal EMFContinuous DC Mode is required when measuring the resistance of highly inductive components such as transformersPulsed Mode is important when measuring heat sensitive components such as thermistors.dry circuit” measurementsThis thing has amazing specs <=10 ohms. Above 10 Ohms My 8846A is more accurate. it is even more accurate than the Agilent 3458A below 130m Ohm's. Only The 34402A is better and only by a factor of 2 from .01 Ohm and below. And the 8846A is better than the 34420A at 1 Ohm and above. Just shows you have to calculate actual reading errors and through all ranges to gage performance. It settles instantly and only bobles 1 digit (1 micro Ohm) I am one happy camper!Table of Performance comparisonOhm 1 year +/_% error of specific valueValue LOM-501A 8846A 3458A 34420A0.0001 4.02 3000 50 2.00.001 0.42 300 5. 0.20.01 0.06 30 0.5 0.0270.1 0.044 3.01 0.05 0.0090.14 0.037 0.0371.0 0.04 0.31 0.006 0.00710.0 0.04 0.04 0.002 0.006Pics below

author: Baliszoft
author_rank: Frequent Contributor
timestamp: March 08, 2012, 05:01:54 pm
content: I like the PCB. I am wondering like it was hand drawn (designed)...

author: robrenz
author_rank: Super Contributor
timestamp: March 08, 2012, 05:05:56 pm
content: Probably manualy done with the old tape and sticker method.

author: Rufus
author_rank: Super Contributor
timestamp: March 08, 2012, 05:25:01 pm
content: Quote from: robrenz on March 08, 2012, 06:00:01 amFor 2000 bucks you would think they could have afforded some solder resist.

author: robrenz
author_rank: Super Contributor
timestamp: March 08, 2012, 05:47:40 pm
content: Made in 1987. Was solder mask prevalent back then?Also found out calibration with data (ISO17025) By IET is $469.00 ouch!

author: Unknown
author_rank: Unknown
timestamp: March 08, 2012, 05:59:26 pm
content: Solder mask was definitely commonly available in 1987. I wouldn't be surprised if it was designed much earlier, I don't think these hand-made PCB masks were common in 1987. Was this hand-soldered? If they still use the same design, than that might explain the high price.

author: robrenz
author_rank: Super Contributor
timestamp: March 08, 2012, 06:19:09 pm
content: I have not seen the bottom, and I am no expert but from the top it looks awfully smooth for hand soldering except the big electrolytics look hand soldered.

author: FenderBender
author_rank: Super Contributor
timestamp: March 09, 2012, 02:45:27 am
content: Quote from: robrenz on March 08, 2012, 05:47:40 pmYes. I have a 1975 Tektronix scope with good old green solder mask.

author: muvideo
author_rank: Frequent Contributor
timestamp: March 09, 2012, 09:36:12 am
content: Thank you for the teardown, do they still make and sell it?It would be interesting to compare with a new oneto see if there is any difference in 25 years, I imagine thatsome of the components are not available anymoreFabio.

author: robrenz
author_rank: Super Contributor
timestamp: March 09, 2012, 11:44:44 am
content: Quote from: muvideo on March 09, 2012, 09:36:12 amYes, IET is marketing it now.http://www.ietlabs.com/lom-510.html

author: SeanB
author_rank: Super Contributor
timestamp: March 10, 2012, 10:31:14 am
content: Nice, but i will stick with my bridge, where I can watch resistors heating up if I touch them. 4 D cells for power, but now is using 4 alkaline C cells and a spacer to fit, much cheaper to buy and use. Life will still be shelf life. At least i di make a zero reference shunt, using a copper foil to short the terminals, wire had an offset of about 10 milliohms.

author: robrenz
author_rank: Super Contributor
timestamp: March 10, 2012, 01:33:10 pm
content: Quote from: SeanB on March 10, 2012, 10:31:14 amI didn't get the correct din plug yet to make up a set of kelvin clips and kelvin probes so I just used 4 short jumper clips to make sure the unit worked. I was measuring a 3" length of 22AWG wire and I could breath on it and see the resistance rise and then fall as it cooled. Touching the wire gets an instant jump in resistance that takes longer to return to the original reading. I got this to calibrate the low ranges of decade boxes I am making so a manual bridge would not be practical for me from a time per measurement perspective.

author: SeanB
author_rank: Super Contributor
timestamp: March 11, 2012, 01:49:53 pm
content: Takes 2 minutes per measurement, but I do it so infrequently it is no problem.

author: robrenz
author_rank: Super Contributor
timestamp: March 11, 2012, 05:41:34 pm
content: Can you tell me a little about your bridge? (I am sincerely interested, not trying to start a battle which is better). What level oftraceableaccuracy can you achieve at 20m Ohm? I would need +/- .04% just to match the accuracy of the unit to use for calibrating it. It has separate trims for each range. I only realy care about the 20m Ohm and 200m Ohm ranges.

author: SeanB
author_rank: Super Contributor
timestamp: March 11, 2012, 07:50:39 pm
content: Itt is a Yokogawa bridge I got from a flea market, a little rat nibbled case wise, a few hundred roach droppings to clean out from the carry case but basically clean and sound inside. Tested with the few precision resistors i have around, and was pretty much within 1 digit on all of them. New batteries and it worked ( after a little googling to get the manual to replace the rat eaten scraps inside) for me.See for detailhttp://tmi.yokogawa.com/products/portable-and-bench-instruments/dc-precision-measuring/2755-precision-wheatstone-bridge/0.6% accuracy at the ranges you need, but it is within this spec. Most due probably due to contact resistance, even after cleaning all the switches with cleaner and general clean up. Checked the Zero with a copper foil shunt I made to fit the terminals, pretty close to zero as I can get without a 4 wire ability. Mostly meant to find cable faults, have used it to check windings for shorts on motors.

author: robrenz
author_rank: Super Contributor
timestamp: March 11, 2012, 08:20:19 pm
content: Thanks, if I read correctly it would be .1% at 1 Ohm but I need 0.02 ohm to calibrate the 20m Ohm range.

author: free_electron
author_rank: Super Contributor
timestamp: May 07, 2012, 03:22:32 pm
content: looks like a clone ( or very close approximation) of the keitlhey 485 microohmmeter...the reason for not having soldermask is ... leakage !when you are makeing very precise systems you cannot put soldermask over those area's.since this thing has such a large area that would be void of soldermask they opted to have none at all.

author: robrenz
author_rank: Super Contributor
timestamp: May 07, 2012, 03:31:48 pm
content: It is actualy a Cambridge technology meter. They are out of business and I guess IET bought the manufacturing rights. I think you meant the kiethley 580 the 485 is a Picoammeter. But the LOM-510 has better specs and resolution than the 580.

author: free_electron
author_rank: Super Contributor
timestamp: May 07, 2012, 05:22:25 pm
content: eh yes. 580. got my numbers confused there.the guts look similar ( same chips ... )

author: FenderBender
author_rank: Super Contributor
timestamp: May 09, 2012, 03:53:26 am
content: Quote from: Rufus on March 08, 2012, 05:25:01 pmDon't be silly now. $2000 and you want solder mask? Silly goose.

author: robrenz
author_rank: Super Contributor
timestamp: May 11, 2012, 11:06:31 am
content: Another one available at a much higher price. This one was hiding under this unique spelling "micro ohmeter"http://www.ebay.com/itm/Cambridge-Micro-Ohmeter-Model-510A-115V-60Hz-/250771174338?pt=LH_DefaultDomain_0&hash=item3a632073c2Edit: I let you guys have a chance for a few months but I could not resist any longer. Got it for $200.00testing and calibration shown later in this thread.

author: robrenz
author_rank: Super Contributor
timestamp: July 17, 2012, 10:45:22 am
content: I added a switch to the 510 meter to allow pulsed switched mode offset compensated ohms from the front panel. Also created a new graphic overlay to accommodate the switch and update the looks of the meter. I show a comparison of the max error specs of the following meters, IET LOM-510, 8846A, 34420A, 34411A, and 3458A.Video errata: Current pulse is 166 mS not 0.166 mS

author: Unknown
author_rank: Unknown
timestamp: July 17, 2012, 12:28:19 pm
content: Neat job with the face plate. Thubs up!

author: robrenz
author_rank: Super Contributor
timestamp: July 17, 2012, 01:44:51 pm
content: Thanks HAL-42b, I have to work on getting the "ah's" out of my vocabulary. Sounds ridiculous when I hear it. Video skills need a lot of work also. Makes you realize how good Dave is at it.

author: Unknown
author_rank: Unknown
timestamp: July 17, 2012, 05:23:50 pm
content: Quote from: robrenz on July 17, 2012, 01:44:51 pmNever noticed anything odd in the video. Sounds totally normal to me.But now that you said it, I start to worry about my voice once I hear it on video, which is supposed to happen in near future.

author: billclay
author_rank: Regular Contributor
timestamp: July 24, 2012, 11:36:05 pm
content: Nice video, and great job on the front panel!Can you post the data from the spreadsheet/graph? Thanks.

author: robrenz
author_rank: Super Contributor
timestamp: July 25, 2012, 12:40:46 am
content: Here is the excell spreadsheet of the low ohms accuracy comparison.Vertical axis is logaritmic maximum +/-% ofreadingerror.EDIT: See chart as picture with additional meters in later posts

author: robrenz
author_rank: Super Contributor
timestamp: September 02, 2012, 09:49:14 pm
content: I just got my LOM-510A calibrated by IET labs. The meter is 25 years old and had no signs of previous calibrations. Cal data shown below. The stability of this meter at 1 micro Ohm resolution is truly amazing. I have done enough testing with it to know that anything other than a rock steady reading or a perfectly consistent LSD bobble between two readings means something thermal is going on. This seems like the "Power Designs" of micro-Ohm meters, no frills, no programming, just exceptional accuracy even by today's standards.I also made a stupid low $200.00 offer on another unit on EBay and got it. Perfect condition and I checked/calibrated it against the IET calibrated unit as shown below. All ranges were in spec as recieved. Even though I adjusted the second unit to agree exactly with the calibrated unit on all ranges, some could argue there could be transferal errors. Even if I add 1LSD to the calibrated units error on each range it is still well within the .02% of reading + 2LSD + 2microOhm specification. So I feel confident the second unit is well within spec.Calibration dataBoth units warmed up and on the same range and are measuring in switched mode. Cables are clamped so that nothing moves when I switch the plug from one unit to the other.Piece of tinned copper wire used for the .010 Ohm test. I just adjusted the spacing of my ultimate Kelvin probes to get a nominal 10 mOhm reading.The Thermal coefficient of resistance of the copper wire requires the use of a insulated box to prevent variations from drafts and my body heat. just made one out of a piece semi rigid foam.Chunk of iron holding the foam box tight to the table top.The calibrated meter with the reading stabilized at 10.022 mOhm. The probe plugs are then interchanged between the two meters.The second meter's 20 mOhm range trim pot is adjusted until the reading is stable at 10.022 mOhm. The probe plugs are interchanged a couple of times making sure the readings are identical between the meters. The meters cover is kept on all the time except to make a trim pot adjustment to keep the meter internal temperature consistent.Comparison and adjustment on the other ranges was done using my decade resistance box. These are 25 ppm resistors and are heat sinked so they were stable without any additional thermal control.

author: Unknown
author_rank: Unknown
timestamp: September 03, 2012, 12:00:13 am
content: Amazing!

author: Daniyal
author_rank: Contributor
timestamp: September 03, 2012, 03:15:00 pm
content: great post!!

author: SeanB
author_rank: Super Contributor
timestamp: September 03, 2012, 03:38:35 pm
content: Lovely technique, like the isothermal block you made, and the nice simple ways used. Very nice, makes my measurements look crude. All I can get is a 10mOhm resolution on a 10R resistor, but it is not 4 wire, just a bridge.

author: robrenz
author_rank: Super Contributor
timestamp: September 04, 2012, 01:20:46 am
content: I finally figured out how to convert excel to pdf to jpg so I could post the low Ohms comparison chart as a picture. Also added the Keithley, Megger, and AEMC to round out the comparison. Chart is% of readingerror values. 8846A and 34411 are identical above 13 Ohm. It is interesting to see they all have thier strengths and weaknesses. I would put the 34420 as the winner and the LOM-510A as second for the 1 Ohm to 1 mOhm span.Max. drive current and resolution.MEGGER DLRO 10 10A drive 0.1u Ohm resolutionAEMC 6250 10A drive 0.1u Ohm resolutionKIETHLY 580 100mA drive 10u Ohm resolutionLOM-510A 1A drive 1.0u Ohm resolutionAGILENT 34411 1mA drive 100u Ohm resolutionFLUKE 8846A 5mA drive 10u Ohm resolutionAGILENT 34420 10mA drive 0.1u Ohm resolutionAGILENT 3458A 10mA drive 10u Ohm resolution

author: andyb
author_rank: Regular Contributor
timestamp: September 06, 2012, 01:01:55 am
content: Wow! What is that resistor decade box? Did you make it? I googled a bit for Versa-Ohm, and came up empty.

author: robrenz
author_rank: Super Contributor
timestamp: September 06, 2012, 01:58:32 am
content: I was wondering how long it would take for someone to notice that. It is my own design and name. I did the same thing you did, I thought up a name and then googled it to make sure no one else had used it. It isTWO8 decade units in one box. The resistors 10 ohm and up are 0.1% .25 watt 25ppm and are heat sinked. The heat sink fins are on the back and that is why it is sitting in that orientation for optimum convection cooling. It also has a forced fan cooling attachment for higher accuracy or dissipation. All the individual decades are available separately so you can get many resistance values out of it simultaneously with supplied calibrated jumpers. Special jumpers allow paralleling up to 20 resistors to get down to .01 ohm at 5W. I will be posting a thread/video about all its features soon and there will be a whole series of detailed videos on its design and construction. And yes they will be for sale, I made a first run of 25. I am just finishing up some of the jumper attachments now. Stay tuned!

author: andyb
author_rank: Regular Contributor
timestamp: September 06, 2012, 10:52:30 pm
content: Very cool! I fall into the camp of folks who've never really seen a use for substitution boxes, but this may change my mind! I'll be watching!

author: sorin
author_rank: Frequent Contributor
timestamp: January 15, 2013, 09:27:55 pm
content: Has anyone got a schematic, or the service manual?

author: robrenz
author_rank: Super Contributor
timestamp: January 15, 2013, 09:41:06 pm
content: TheManualtalks about how the circuitry works including chip numbers and referring to a nonexistent schematic. I have not found a schematic so far but I don't really need one the circuit is a very simple 2 sided board.

author: sorin
author_rank: Frequent Contributor
timestamp: January 16, 2013, 12:10:44 pm
content: I want to build from scratch my "Micro Ohm meter" based on this schematic.Thanks for your reply.

author: ass20
author_rank: Regular Contributor
timestamp: February 08, 2023, 09:28:07 pm
content: hiwhere i can see shematic of 510micro-ohm meter?