Fluke 337 clamp meter hall sensors - Page 1
Forum section: electronics / repair

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 22, 2024, 07:25:36 pm
content: I recently bought a broken Fluke 337 current clamp to attempt to repair.As advertised the meter is working except for current measurements.Measuring at the 8 conductor FPC connector leading to the clamp showed that only 1 connection to the hall sensors out of 4 was uninterrupted.After prying the active side of the jaw open, the red plastic cover to the inner hall sensor was unstuck, removing it completely finished tearing the sensor from the FPC as the sensor remained embedded in glue in the plastic cover.Although it wasn't obvious from the outside I assume the meter had one too many falls and that unstuck the iron core in the jaw tearing at the FPC on the better glued sensor.The outer sensor has freed itself from the glue without damage, I have tried to identify what type it is although the markings are hard to read it seems to be something like 54 / 24 / 34 or 84... It's a SOT-23-4 package.I have no previous experience with his type of repair still I'd like to try to replace the ripped sensor, I doubt I'll be able to release it from the glue without destroying it, I've tried Acetone but that's softening the plastic more than the glue.Why would they use 2 sensors rather than a single? Would they be of different type or same type with different bias and gain?I've been looking for SOT-23-4 models and haven't found many. A couple are the Toshiba THS124 and AKM HW-101A.Any clue on what Fluke may have used here?

author: floobydust
author_rank: Super Contributor
timestamp: February 22, 2024, 09:10:54 pm
content: It's a SOT-143 package, search for that. One pin is wider than the others. Big players like Honeywell, Allegro I would look at first.Sorta looks like a "4-" is hand-scratched on the top, I wonder if the sensors are ranked? Try wet the top and see if part numbers are easier to read.Did findhttps://www.hallsensors.dehas some info, CYSJ3A-S "P3A" or CYSJ15A-S "15A" marking code.Two Hall sensors can be used to cancel out drift effects like temperature which is a problem for Hall sensors.

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 23, 2024, 12:20:38 am
content: Thanks for your input floobydust.Even peering at it with the stereo microcope at different lighting angles I'm not getting much other than the "4", it looks laser engraved not hand scratched.As for markings the ChenYang CYTHS124 looks like a good candidate and it's a linear model. (That appears to be equivalent to the Toshiba THS124.)

author: floobydust
author_rank: Super Contributor
timestamp: February 23, 2024, 03:21:57 am
content: It's difficult with only a "4" marked on the part and no Fluke schematic or service manual out there. I'd order some and give it a try.ElektroTanya FLUKE 333--337 CLAMP METER CALIBRATION 1999 SMhttps://www.opweb.de/english/company/Fluke/333not much help, no sch or Hall sensor part #.I would carefully use heat maybe to get the glue off.Check the clamp meter is not in the May 15, 2009Fluke 33X Recall, CPSC"Digital Clamp Meters Recalled by Fluke Due to Shock Hazard".

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 03, 2024, 10:51:18 pm
content: I can only agree that's a little short of information, I've taken my chances and ordered some of the Toshiba parts on AliExpress.At least I still have one of the original sensors in a full piece so I'll be able to do some electrical comparison when they arrive.I tried removing the one set in the glue, things didn't work out well...Thanks for pointing me to the calibration manual, after overviewing it I found this step of the adjustment could be linked to the existence of 2 sensors in the jaw:8. Change to the A AC function.9. Apply 100.0 A 50 Hz.10. Note measurement with wire at top and bottom of jaw opening.11. Adjust R9 until this difference is within 1.0 A.My meter's serial isn't in the recalled models, interesting to know though, I wasn't aware of these recalls at all.

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 09, 2024, 02:03:23 am
content: THS124 parts arrived from Ali a few days ago, I only had time to do some comparative resistance measurements with the remaining original sensor when I received them.This evening (early hours) I got round to a little repair work that started by gluing the FPC back to the 1/2 core and patching broken tracks.When I got to fitting the new sensor I'd previously handled for the resistance measurements the leads had turned black, I suppose they're tin plated copper and don't like sweaty hands at all.After some scratching the sensor was super-glued in place (no pads left to solder it on) before leading the last wires to it, luckily the place where the larger pad was was still recognisable avoiding me some reverse engineering to find out which way it should be mounted.Before going any further I fitted the bits back together for a quick DC test, that went quite well too considering there's still some glue that needs milling away in one of the red caps. It feels like it should be in range of readjustment once I've finished cleaning-up and deciding how to reassemble trying to avoid the tear issues caused by the original glue.The hard glue isn't a problem as long as the meter isn't dropped too hard, still I'd prefer using something softer.

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 11, 2024, 12:21:47 am
content: Getting to the end of the adventure tonight.Glued the end caps with a small amount of silicone, the 1/2 core and 1/2 jaw set in epoxy with wedges to hold the core in place.The readjustment wasn't much fun, I had to learn so I touched all the trimpots even those that may have still been OK (AC V) anyway they mostly needed adjustment, the previous owner had been desperate at trying to do something about it.Most of it is easy enough, the 100A DC is annoying because it will magnetise the core then once the current is removed you're left with a DC offset.A note on this:I tend to disagree with Fluke's document. AFAICT the previously mentioned steps 8 to 11 should be forA DCadjustment.The way it went here was:7. Adjust DC offset.8. Stay set on A DCdo not switch to A AC.9. Apply 100.0 ADC.10. Note measurement with wire at top and bottom of jaw opening.11. Adjust R9 until this difference is within 1.0 A. (And this is a tough compromise, you have absolutely no effect on the balance between top and bottom of the jaw, just aim that when the conductor is ideally centred you get the right reading and that the off-centre deviation is about symmetrical around this point)It was an interesting repair (for me at least), however I'm not looking forward to doing another of the kind soon.