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

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

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

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#ElectronicsCreators #Fluke #Hack

[EEVblog]

FYI, Fluke responded, the 70 series not not being discontinued, it's just not on the Australian website. It is on the US website main page though.

[bobcuyt]

so: 10 cents for the cap, and 10, 000 dollars for the calibration equipment? ;)

[iamdarkyoshi]

"Convert your fluke meter with only 10 cents worth of parts!*"

*cal lab not included, batteries sold separately, adult supervision required

[jrb_sland]

My wife bought me an original Fluke 77 as a wedding gift in 1985. Still my favourite rugged, reliable DVM. Last year she found me {through her volunteer position with a local thrift shop here in western Canada} an older Simpson 470 DVM which is NOT auto-ranging, an advantage when I want to quickly check zinc-carbon, alkaline, NiCd & NiMH cells using the 2 volt range. I'll grant that modern metrology tools are generally superior, but instruments from many decades in the past still have their uses. I have a 1941-vintage 0 - 15 VDC meter made by Weston. Nicely finished wooden case, long mIrrored scale, still very accurate, but a little overdamped {slow to reach its final reading}. Calibration certificate inside the lid signed in india ink. 6 years older than I am !

[MiniLuv-]

Gee's its really obvious in this video how much work you have to put into a single video. Thanks.

[benupde]

I just checked and my second Fluke is indeed a 77 IV from my time in the US Army. She’s going on 20 years old and still works like a champ.

[eponte]

I work for a transformer manufacturer company and when measuring excitation and no load loss of the transformer with no load connected the ieee standard calls for use of both an rms and avg reading meter. We use fluke 87 and 83 respectively for this. Has to do with confirming a sinusoidal waveform is being applied. If the values of each meter are off we have to apply a correction factor. And we annually get our meters calibrated by a third party cal lab to instill confidence in the measurements.

[arrx]

I thought I replied but it doesn't look like it went thought here's my comment again: To clarify/correct something around the 2-3min time mark: The 17x model is 20 years old but it has been updated internally since 2001. I have a preproduction revision from the 2004ish refresh that I can share photos of on the forum if there's interest. IDK if there's been updates sense but I'd be interested to compare mine with the current PCB.

[JustinEmlay]

Reminds me of the old school Radio Shack days. They would have something like 3 different radio models, low cost, middle cost and high cost. The higher cost ones supporting a larger range of bands. All you had to do was buy the cheaper one, cut a few resistors and bam, you have the most expensive radio.

[typxxilps]

I have not much clue about electronics, barely know what a diode is and a capacitor, but I like these videos cause I could follow your shematics and ideas at least and learned a lot.
I also had watched that previous video or from the other channel about the story why they are so expensive.

Thanks a lot.

[nameredacted]

Dave geeking out, as usual!
Yes, it is a very, very good idea to sell exactly same PCB (and 99% CCA) as multiple products.

[Digital-Dan]

This kind of approach goes way back. In the late 50's and early 60's the IBM 407 accounting machine was available (for rent only) for one price, and a double-speed version rented for a higher price. In order to make this change, a jumper was removed. I guess there was some mechanical wear argument for the increased price. I'm sure this is not the only example.

[alexanderoransky]

Awesome upgrade and cal video! Hilariously though, 177 sells for $311 on Amazon US vs 77 for $323.

[jeffm]

Good audio power amp with a step down transformer to get the 6 amps AC. Tearing down an old UPS backup can sometimes do the trick. I've also used the same to get up to 1000 volts AC with well a step up transformer. Using the audio amp with the function gen.

[budi]

On brymen DMM you can have nice thing of calibrating just the mode selection dial of your choice without the need to calibrate whole function or even whole full range of that particular measurement selection.

[bill]

It would appear that if Fluke had added a tiny bit more circuitry, they could have maybe a small mosfet switch the filter cap in and out of the circuit on demand. Then a button on the front panel could select AVG/RMS. during calibration, pressing the yellow button could tell it to take two readings, one with the cap in and one with it out. I think building two models with such a minor difference was a missed opportunity considering it could have just had both modes in one.

[savvytech]

You sir, are a damn GENIUS!! The world loves you for ALL the right reasons! <3

[Iosens]

Hi Dave, thanks BTW for stopping the trend you almost started 3 months ago. Your content speaks for itself!

[LogiForce]

The 70 series is still offered on the site from the Netherlands but "Out-of-stock".
Also at 4:22 look at the top PCB writting... it's a "FLUKE 17X-30111 REV 015" board! Mystery has been solved! 😉 (Edit: DOH! Says it one second after I stopped the video. 🤦‍♂️😅 )

[IliyaOsnovikov]

Fluke 76 was True RMS back in the 90-s when I've bought it. Works untill today just as new.