Author Topic: IET LOM-501A Micro Ohm meter (Read 41026 times)

robrenz · « **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!

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

Baliszoft · « **Reply #1 on:** March 08, 2012, 05:01:54 pm »

I like the PCB. I am wondering like it was hand drawn (designed)...

robrenz · « **Reply #2 on:** March 08, 2012, 05:05:56 pm »

Probably manualy done with the old tape and sticker method.

Rufus · « **Reply #3 on:** March 08, 2012, 05:25:01 pm »

Quote from: robrenz on March 08, 2012, 06:00:01 am

Current starting price from IET is $1975.00

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

robrenz · « **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 · « **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.

robrenz · « **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.

FenderBender · « **Reply #7 on:** March 09, 2012, 02:45:27 am »

Quote from: robrenz 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!

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

muvideo · « **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.

robrenz · « **Reply #9 on:** March 09, 2012, 11:44:44 am »

Quote from: muvideo 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.

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

SeanB · « **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.

robrenz · « **Reply #11 on:** March 10, 2012, 01:33:10 pm »

Quote from: SeanB 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.

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.

SeanB · « **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.

robrenz · « **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.

SeanB · « **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.

robrenz · « **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.

free_electron · « **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.

robrenz · « **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.

free_electron · « **Reply #18 on:** May 07, 2012, 05:22:25 pm »

eh yes. 580. got my numbers confused there.
the guts look similar ( same chips ... )

FenderBender · « **Reply #19 on:** May 09, 2012, 03:53:26 am »

Quote from: Rufus on March 08, 2012, 05:25:01 pm

Quote from: robrenz on March 08, 2012, 06:00:01 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.

robrenz · « **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

testing and calibration shown later in this thread.

robrenz · « **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

HLA-27b · « **Reply #22 on:** July 17, 2012, 12:28:19 pm »

Neat job with the face plate. Thubs up!

robrenz · « **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 · « **Reply #24 on:** July 17, 2012, 05:23:50 pm »

Quote from: robrenz 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.

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.


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Author Topic: IET LOM-501A Micro Ohm meter (Read 41026 times)

alm

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