FLUKE DMM HACK adds ONE DIGIT TO design NUMBER
among his numerous interests, [Dave Jones] likes test as well as measurement equipment. He just recently published a few videos on his EEVblog checking out the reasons why Fluke voltmeters are so expensive. In the process, he stumbled upon an fascinating hack for the Fluke 77.
The Fluke 77 was introduced in 1983, as well as is an typical responding meter in the AC modes. This design has ended up being a de-facto basic for utilize in maintenance depots as well as labs for devices which has extremely long lifespans — believe armed forces as well as industrial gear, for example. numerous test procedures as well as training materials have been developed around the utilize of the the Fluke 77. The expense to modification them when a new as well as much better meter comes along is typically so prohibitive they may also be cast in stone — or at least hammered into 20 pound fanfold paper by a WordStar-driven daisy-wheel printer. however for those unburdened by such tradition requirements, Fluke has the 17x series of true RMS reading meters from because the beginning of this century. These meters bear a strong visual resemblance to their siblings in the 7x household as well as are substantially interchangeable however for their AC measurement methods.
In the process of tearing down a Fluke 77 meter for one more reason entirely, [Dave] discovers that the resemblance it not just visual. Not only is the 77’s PCB identified 17x, however there is an Analog gadgets AD737 true RMS to DC converter IC on the board.
What gives? Why would they go to the cost to put this chip in an typical responding meter?
A bit much more digging into the data sheet exposes this chip can determine in three different modes: true RMS, typical rectified, or absolute values. choosing true RMS mode needs adding just a single 33 uF capacitor. sure enough, in the Fluke schematics this is clearly shown as an optional load.
Not surprisingly, [Dave] does the adjustment as well as it works. The only drawback is that after you make this change, you have to carry out a total recalibration of the meter. Annoyingly, there doesn’t appear to be any type of method to just calibrate the AC measurements, for example. Unless you’re a recuperating test devices addict like [Dave], you most likely don’t have all the gear close-by to carry out this calibration yourself — something to keep in mind if you try this at home. one more thing to note is that this hack was done on a contemporary Fluke 77 IV meter. If you have a Fluke 77 from 1985, this hack doesn’t apply.