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EEVblog 1448 - Convert a Fluke 77 IV to True RMS for 10 CENTS

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How to convert a Fluke 77 IV average responding multimeter into a True RMS model 177 for 10 cents.
Should also work for converting a Fluke 83V to 87V
True RMS measurement vs Average Responding
And calibration of a Fluke meter.

00:00 - Hacking a Fluke 77 IV Multimeter
00:35 - Is the Fluke 70 series discontinued?
01:15 - Fluke History
03:10 - I noticed something...
04:49 - The AD737 True RMS converter chip
06:04 - Theory of Operation
07:21 - What is Crest factor
08:58 - How do they do it?
09:25 - Fluke 87V Schematic and the custom ASIC
10:53 -  Let's modify it!
12:58 - A sine wave is NOT a crest factor of 1
14:01 - Soldering
15:15 - Will it work?
16:46 - Calibration procedure
20:09 - Winner Winner Chicken Dinner

Dave, you said in the video you'd include a link to the 87V service manual - I couldn't see this - did you forget?

Did a little digging and found it here! Downloaded it myself too.


* Buy a DMM where 1/3 of the price is calibration.
* Pay 10¢ to modify it.
* No longer have calibration
Sorry, I just had to make that comment ;) . Don’t take it too seriously, I am fully aware people would buy Fluke for reasons other than calibration.

yeah.  10 cents.  It is kind of like when I do my own auto repairs.  I save hundreds of dollars over taking it into the shop.  But that ignores the literally thousands of dollars of tools I have accumulated over the years (and the not insignificant amount of blood donated to various vehicles and soap used in cleaning up).  The accounting does come out in my favor over all of the repairs that have been done and I know the quality of the work (both good and bad) so it works out, but it sure isn't for everyone.

On the other hand, it is really neat to have discovered this and to be able to do it.  Good on you, Dave.


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