Author Topic: IET LOM-501A Micro Ohm meter  (Read 28106 times)

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Offline robrenz

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IET LOM-501A Micro Ohm meter
« on: March 08, 2012, 06:00:01 am »
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 page http://www.ietlabs.com/lom-510.html
Data sheet http://www.ietlabs.com/pdf/Datasheets/LOM-510A_530.pdf
Manual http://www.ietlabs.com/pdf/Manuals/LOM-510A_im.pdf

It has 4 measurement modes
  • Switched DC Mode totally eliminates the effects of thermal EMF
  • Continuous DC Mode is required when measuring the resistance of highly inductive components such as transformers
  • Pulsed Mode is important when measuring heat sensitive components such as thermistors.
  • dry circuit” measurements
This 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! ;D

        Table of Performance comparison

Ohm           1 year +/_% error of specific value
Value       LOM-501A    8846A     3458A    34420A

0.0001         4.02         3000       50            2.0
0.001           0.42         300         5.            0.2
0.01             0.06         30          0.5          0.027
0.1              0.044        3.01       0.05        0.009
0.14            0.037                      0.037
1.0              0.04          0.31       0.006      0.007
10.0            0.04          0.04       0.002      0.006       

Pics below







« Last Edit: September 08, 2014, 10:59:48 pm by robrenz »
 

Offline Baliszoft

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Re: IET LOM-501A Micro Ohm meter
« Reply #1 on: March 08, 2012, 05:01:54 pm »
I like the PCB. I am wondering like it was hand drawn (designed)...
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #2 on: March 08, 2012, 05:05:56 pm »
Probably manualy done with the old tape and sticker method.

Offline Rufus

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Re: IET LOM-501A Micro Ohm meter
« Reply #3 on: March 08, 2012, 05:25:01 pm »
Current starting price from IET is $1975.00

For 2000 bucks you would think they could have afforded some solder resist.
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #4 on: March 08, 2012, 05:47:40 pm »
Made in 1987.  Was solder mask prevalent back then?
Also found out calibration with data (ISO17025) By IET is $469.00  ouch! :'(

alm

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Re: IET LOM-501A Micro Ohm meter
« Reply #5 on: March 08, 2012, 05:59:26 pm »
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.
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #6 on: March 08, 2012, 06:19:09 pm »
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.

Offline FenderBender

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Re: IET LOM-501A Micro Ohm meter
« Reply #7 on: March 09, 2012, 02:45:27 am »
Made in 1987.  Was solder mask prevalent back then?
Also found out calibration with data (ISO17025) By IET is $469.00  ouch! :'(

Yes. I have a 1975 Tektronix scope with good old green solder mask.
 

Offline muvideo

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Re: IET LOM-501A Micro Ohm meter
« Reply #8 on: March 09, 2012, 09:36:12 am »
Thank you for the teardown, do they still make and sell it?
It would be interesting to compare with a new one
to see if there is any difference in 25 years, I imagine that
some of the components are not available anymore :)

Fabio.
Fabio Eboli.
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #9 on: March 09, 2012, 11:44:44 am »
Thank you for the teardown, do they still make and sell it?
It would be interesting to compare with a new one
to see if there is any difference in 25 years, I imagine that
some of the components are not available anymore :)

Fabio.

Yes, IET is marketing it now.   http://www.ietlabs.com/lom-510.html

Offline SeanB

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Re: IET LOM-501A Micro Ohm meter
« Reply #10 on: March 10, 2012, 10:31:14 am »
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.
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #11 on: March 10, 2012, 01:33:10 pm »
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.

I 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.

Offline SeanB

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Re: IET LOM-501A Micro Ohm meter
« Reply #12 on: March 11, 2012, 01:49:53 pm »
Takes 2 minutes per measurement, but I do it so infrequently it is no problem.
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #13 on: March 11, 2012, 05:41:34 pm »
Can you tell me a little about your bridge?  (I am sincerely interested, not trying to start a battle which is better). What level of traceable accuracy 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.

Offline SeanB

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Re: IET LOM-501A Micro Ohm meter
« Reply #14 on: March 11, 2012, 07:50:39 pm »
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 detail

http://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.
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #15 on: March 11, 2012, 08:20:19 pm »
Thanks,  if I read correctly it would be .1%  at 1 Ohm  but I need 0.02 ohm to calibrate the 20m Ohm range.

Offline free_electron

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Re: IET LOM-501A Micro Ohm meter
« Reply #16 on: May 07, 2012, 03:22:32 pm »
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.
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Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #17 on: May 07, 2012, 03:31:48 pm »
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.

Offline free_electron

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Re: IET LOM-501A Micro Ohm meter
« Reply #18 on: May 07, 2012, 05:22:25 pm »
eh yes. 580. got my numbers confused there.
the guts look similar ( same chips ... )
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Offline FenderBender

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Re: IET LOM-501A Micro Ohm meter
« Reply #19 on: May 09, 2012, 03:53:26 am »
Current starting price from IET is $1975.00

For 2000 bucks you would think they could have afforded some solder resist.

Don't be silly now. $2000 and you want solder mask? Silly goose.
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #20 on: May 11, 2012, 11:06:31 am »
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=item3a632073c2

Edit:  I let you guys have a chance for a few months but I could not resist any longer. Got it for $200.00 ;D  testing and calibration shown later in this thread.
« Last Edit: September 03, 2012, 04:38:36 pm by robrenz »
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #21 on: July 17, 2012, 10:45:22 am »
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

« Last Edit: March 19, 2015, 02:59:45 am by robrenz »
 

HLA-27b

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Re: IET LOM-501A Micro Ohm meter
« Reply #22 on: July 17, 2012, 12:28:19 pm »
Neat job with the face plate. Thubs up!
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #23 on: July 17, 2012, 01:44:51 pm »
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.

HLA-27b

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Re: IET LOM-501A Micro Ohm meter
« Reply #24 on: July 17, 2012, 05:23:50 pm »
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.

Never 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.
 

Offline billclay

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Re: IET LOM-501A Micro Ohm meter
« Reply #25 on: July 24, 2012, 11:36:05 pm »
Nice video, and great job on the front panel!
Can you post the data from the spreadsheet/graph?  Thanks.
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #26 on: July 25, 2012, 12:40:46 am »
Here is the excell spreadsheet of the low ohms accuracy comparison.
Vertical axis is logaritmic maximum +/-% of reading error.

EDIT:  See chart as picture with additional meters in later posts
« Last Edit: September 05, 2012, 01:00:49 pm by robrenz »
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #27 on: September 02, 2012, 09:49:14 pm »
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 ;D ;D ;D. 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 data


Both 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.
« Last Edit: September 08, 2014, 11:02:36 pm by robrenz »
 

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Re: IET LOM-501A Micro Ohm meter
« Reply #28 on: September 03, 2012, 12:00:13 am »
Amazing!
 

Offline Daniyal

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Re: IET LOM-501A Micro Ohm meter
« Reply #29 on: September 03, 2012, 03:15:00 pm »
great post!!
 

Offline SeanB

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Re: IET LOM-501A Micro Ohm meter
« Reply #30 on: September 03, 2012, 03:38:35 pm »
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.
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #31 on: September 04, 2012, 01:20:46 am »
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 reading error 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 resolution
AEMC 6250            10A drive  0.1u Ohm resolution
KIETHLY 580     100mA drive   10u Ohm resolution
LOM-510A              1A drive   1.0u Ohm resolution
AGILENT 34411    1mA drive  100u Ohm resolution
FLUKE 8846A       5mA drive    10u Ohm resolution
AGILENT 34420  10mA drive   0.1u Ohm resolution
AGILENT 3458A  10mA drive    10u Ohm resolution

« Last Edit: September 07, 2014, 01:42:40 pm by robrenz »
 

Offline andyb

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Re: IET LOM-501A Micro Ohm meter
« Reply #32 on: September 06, 2012, 01:01:55 am »
Wow! What is that resistor decade box? Did you make it? I googled a bit for Versa-Ohm, and came up empty.
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #33 on: September 06, 2012, 01:58:32 am »
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 is TWO 8 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! :D
« Last Edit: September 09, 2012, 12:33:26 am by robrenz »
 

Offline andyb

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Re: IET LOM-501A Micro Ohm meter
« Reply #34 on: September 06, 2012, 10:52:30 pm »
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!
 

Offline sorin

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Re: IET LOM-501A Micro Ohm meter
« Reply #35 on: January 15, 2013, 09:27:55 pm »
Has anyone got a schematic, or the service manual?
 

Offline robrenz

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Re: IET LOM-501A Micro Ohm meter
« Reply #36 on: January 15, 2013, 09:41:06 pm »
The Manual talks 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.

Offline sorin

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Re: IET LOM-501A Micro Ohm meter
« Reply #37 on: January 16, 2013, 12:10:44 pm »
I want to build from scratch my "Micro Ohm meter" based on this schematic.
Thanks for your reply.
 


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