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Old Fluke Multimeters

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Marvin:
Hi DRT! Thanks for really good information.

There has been recently (for a few years) army surplus Fluke 27/FM (not the usual 27 that Dave did a review and input protection tutorial on) coming to ebay etc. I bought one myself and was just trying to research it (it's not broken, just thinking about how it works etc). As this was produced exclusively for the US Army the schematic is unavailable (I have googled for days). The schematics for the the non FM model (so averaging non-true-rms) 27 are available from Fluke. So this was a long introduction but what interests me (and maybe someone else too) is that the 27/FM has True-RMS feature. And what is even more interesting is that it's not AD636, AD736 or some other Analog Devices true-rms converter but it looks like this: see attached image (image loaned from another forum).

With markings SC77174 that gives no google other results than a Chinese forum where someone just wrote that his 27/FM contains it. And it is clearly manufactured by Motorola.

Your posts about the original 8060 Fluke designed and Motorola produced rms converter chip is the only information about this on the internet! I was trying to find a rms converter chip manufactured by Motorola etc, to no avail until I found this thread!

Could this be the final model that had a true Fluke designed true-rms converter inside?

drtaylor:
That is indeed the TRMS converter designed for the 8060. A Fluke Engineer designed and The fab line was, if I remember correctly, Motorolas BiFET. It had to have high performance bipolar transistors for the log-antilog circuitry. If you saw my 8060 initial schematic, it has a block diagram of that chip. I had some more detailed design docs, but it hasn't been seen in years. It's all moot since even Fluke could not get them after Motorola broke into parts.

Marvin:
Thanks DRT for the answer!

I now dove deeper into google and lo behold - MrModemheads 8060A repair has a nice picture of the original RMS chip and I'll be damned - it is even marked the same!

http://mrmodemhead.com/blog/wp-content/gallery/f8060a_00-4/F8060A_016.JPG

So it looks the US Army wanted a true-rms meter and Fluke used the in-house proven but expensive chip even though the 8060A series had already been changed to AD636. The 27/FM is basically identical to the 27 with just the added TRMS chip.


--- Quote from: drtaylor on November 09, 2013, 12:29:51 am ---I had a call from Norm Strong around 1987 who wanted to ask me about design aspects of the components around the TRMS converter. I remember kind of laughing with him because he actually designed the Silicon. I said "com'on Norm, you're the one who helped me optimize it for wide bandwidth. How am I supposed to remember?"

--- End quote ---

I've seen only '87 and '88 date codes on SC77174 chips in 27/FM pictures on forums etc (with '88 being more widely seen, '87 I've see only on one picture). Maybe that is the reason he called you? :D

Excavatoree:
The same IC is in the 8026. .  I suppose it could be a "stripped down" 8060, but it's internals suggest that it is simply an 8020 that has been "souped up" by adding the TRMS capability. 

ChrisGammell:
We've asked Dave Taylor to be on The Amp Hour...and he agreed! He'll be on this week. If you have any questions you'd like us to ask him, let us know.

Forum thread here: https://www.eevblog.com/forum/amphour/drtaylor-(eevblog-forum-member)-on-the-show-this-week/
Subreddit here: http://www.reddit.com/r/TheAmpHour/comments/1uswuh/this_week_on_the_show_dave_taylor_designer_of_the/

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