03-04-2016, 11:58 AM
That IC has an interesting history...
In brief, it was a joint effort between Fluke and Intersil as part of the development of the 8020A - but Intersil launched their own version with a minor modification to get around the exclusivity agreement with Fluke. Apparently they even neglected to remove the Fluke logo from the silicon! As a result, Fluke set up their own silicon fab... See here for the story from the horse's mouth: http://www.eevblog.com/forum/testgear/hi...20-series/
I remember it being second-sourced from Maxim about 20-25 years ago, and probably many others since.
A lot of these cheap multimeters have it as a "COB" (chip on board) under a lump of black resin.
As Dave Taylor notes in his EEVBlog post, the quality of the integrating capacitor is critical, and is usually the first thing to suffer in a cheap multimeter.
Hamid rightly mentions the safety issues.
When you look inside cheap meters, you'll see that little or no attention to detail is present in that area. You're hoping to find generous clearances around input circuits, perhaps with slots routed in the PCB ("clearance" and "creepage"). You're hoping to see MOVs and fusible resistors for input protection, and you want to see decent quality fuses on the current ranges (HRC types - not 20mm glass!). Fluke invest heavily in safety (and naturally market and price accordingly) - a replacement fuse for a typical modern Fluke won't leave much change from a fiver, which makes you a bit careful when measuring on the milliamp range - the fuse for that is usually a 440mA type: http://uk.farnell.com/fluke/943121/fuse-.../dp/546719
The classic tell-tale sign of a multimeter with a cavalier approach to safety is the presence of a transistor tester socket! The pins of which are closely referenced to the common terminal, which in theory could be at any potential relative to mains earth. Be extremely careful when using one of these - keep fingers away from the socket. Naturally, the transistor test function is of zero practical utility anyway - especially when you look at how much better the cheap full-function component testers cost...
I note that many of these cheap meters aren't CAT-rated. We discussed CAT ratings recently in this thread: http://golbornevintageradio.co.uk/forum/...p?tid=5452
To put this into perspective, provided you keep the meter away from high energy circuits, you'll probably be OK (provided you're happy with the poor accuracy, etc). I'd be cautious about measuring mains with these - and I certainly wouldn't go anywhere near a consumer unit with one. Even HT might be dubious, depending on the size of the caps
At the very least, throw away the supplied test probes!
I've told this story before, but some years back a colleague bought half a dozen cheap multimeters from Farnell. They were about £30 each, so not the bottom of the barrel by any means, and they were from a recognised brand. In the space of about 3 years, half of them developed faults. The best one was a problem with the microcontroller locking up intermittently - so you'd see 0.000 VAC on the display, and connect the probes to a source of AC and still see 0.000 VAC. This very nearly killed me when I was checking something powered from the mains - it was only my deep, deep cynicism that saved me. Suffice to say, I enjoyed "widlarizing" that particular meter. That was the final straw for me - all other meters were thrown away or given away if still working (with a stern warning/disclaimer). If we'd spent the money on just 1 Fluke, we'd still have it today, and it would still be in spec, and have another 20 years in front of it. Heck, our primary meters in our electronics lab are 1980s Fluke 75s that have given us an absolutely superb ROI...
In brief, it was a joint effort between Fluke and Intersil as part of the development of the 8020A - but Intersil launched their own version with a minor modification to get around the exclusivity agreement with Fluke. Apparently they even neglected to remove the Fluke logo from the silicon! As a result, Fluke set up their own silicon fab... See here for the story from the horse's mouth: http://www.eevblog.com/forum/testgear/hi...20-series/
I remember it being second-sourced from Maxim about 20-25 years ago, and probably many others since.
A lot of these cheap multimeters have it as a "COB" (chip on board) under a lump of black resin.
As Dave Taylor notes in his EEVBlog post, the quality of the integrating capacitor is critical, and is usually the first thing to suffer in a cheap multimeter.
Hamid rightly mentions the safety issues.
When you look inside cheap meters, you'll see that little or no attention to detail is present in that area. You're hoping to find generous clearances around input circuits, perhaps with slots routed in the PCB ("clearance" and "creepage"). You're hoping to see MOVs and fusible resistors for input protection, and you want to see decent quality fuses on the current ranges (HRC types - not 20mm glass!). Fluke invest heavily in safety (and naturally market and price accordingly) - a replacement fuse for a typical modern Fluke won't leave much change from a fiver, which makes you a bit careful when measuring on the milliamp range - the fuse for that is usually a 440mA type: http://uk.farnell.com/fluke/943121/fuse-.../dp/546719
The classic tell-tale sign of a multimeter with a cavalier approach to safety is the presence of a transistor tester socket! The pins of which are closely referenced to the common terminal, which in theory could be at any potential relative to mains earth. Be extremely careful when using one of these - keep fingers away from the socket. Naturally, the transistor test function is of zero practical utility anyway - especially when you look at how much better the cheap full-function component testers cost...
I note that many of these cheap meters aren't CAT-rated. We discussed CAT ratings recently in this thread: http://golbornevintageradio.co.uk/forum/...p?tid=5452
To put this into perspective, provided you keep the meter away from high energy circuits, you'll probably be OK (provided you're happy with the poor accuracy, etc). I'd be cautious about measuring mains with these - and I certainly wouldn't go anywhere near a consumer unit with one. Even HT might be dubious, depending on the size of the caps
At the very least, throw away the supplied test probes!
I've told this story before, but some years back a colleague bought half a dozen cheap multimeters from Farnell. They were about £30 each, so not the bottom of the barrel by any means, and they were from a recognised brand. In the space of about 3 years, half of them developed faults. The best one was a problem with the microcontroller locking up intermittently - so you'd see 0.000 VAC on the display, and connect the probes to a source of AC and still see 0.000 VAC. This very nearly killed me when I was checking something powered from the mains - it was only my deep, deep cynicism that saved me. Suffice to say, I enjoyed "widlarizing" that particular meter. That was the final straw for me - all other meters were thrown away or given away if still working (with a stern warning/disclaimer). If we'd spent the money on just 1 Fluke, we'd still have it today, and it would still be in spec, and have another 20 years in front of it. Heck, our primary meters in our electronics lab are 1980s Fluke 75s that have given us an absolutely superb ROI...
