Dead meters expose battery terminal design issues

-August 03, 2017

Ever since my consultant days, I have believed that you should not scrimp when it comes to test equipment. Accordingly, when it came time to buy a DVM (digital voltmeter) I spent over $400 on a top-end Fluke meter. I really liked that it measures ac signals with true RMS. The Fluke 187 also has a capacitance meter, and could measure current from microamperes to amperes. I also believe in redundancy, so after a few years I bought a Fluke 189 true RMS meter to keep in the garage for those automotive troubleshooting episodes we all have.

I spent about the same, over $400, for the newer Fluke. These days a Fluke 189 costs $495 new, and a Fluke 187 costs between $465 and $199 refurbished. So I figured I have about $1000 in voltmeters. You can imagine my fury when both meters were dead, even with new batteries (Figure 1).


I opened the battery compartments (Figure 2). While the present batteries in the meters had not leaked, previous leakage had caused severe corrosion on the battery terminals in the case. One nice feature of the meters is that you don’t need tools to open the back, a coin or Buck knife will do the trick. It makes sense that the terminals with the highest voltage had the worse corrosion. The dc return terminal on the far left had no bright finish left on it (Figure 3).





The most positive terminal in the meter was also severely corroded (Figure 4). Note the large fuses Fluke uses for the current measurements. The 1000V ratings make the meter safe to use on higher voltages. I only wish the battery terminals were as well-designed as the fuse terminals.



When I later took the meter apart, I also saw corrosion on the dc bus bar that carries the power (Figure 5). There is no denying the injection molded case is beautiful, with all the features needed to retain the bus bars. It’s a shame the electrical engineers did not specify better plating for the battery terminals.



I attacked the terminal corrosion with my Foredom die grinder and a tiny wire wheel (Figure 6). It seemed to work great, and it looked like it had buffed the terminals down to good metal. I used a brass brush to try and save any plating that was left on the battery terminals.



I was simply mad at the crappy battery terminals. The fury came when the meter still didn’t work, and I got out the second Fluke meter from the garage, and it was dead too. I cleaned its terminals with the wire brush and put in new batteries to no avail. Now I had two dead meters. Two dead meters that cost me about $1000. I figured that one of the terminals must have some non-conductive oxidation, but I couldn’t measure which terminal since I didn’t have a working DVM. So I went to Home Depot and bought this Klein Tools MM600 (Figure 7).



The Klein Tools MM600 induced new waves of fury. There is absolutely no indication on the case how to put in the batteries. I did not unzip the little pouch with the probes and note there was a tiny little manual there. So after a call to the extremely helpful and patient support person at Klein Tools, we figured out where the manual was. Installing the batteries requires unscrewing a Phillips-head screw. There is an incredible amount of verbiage molded into the case (Figure 8). Klein Tools must have more lawyers than usability engineers. All the verbiage were warnings, and the warnings were repeated in French. Thanks, Canada. Dear Klein Tools, please mold in the words “Battery access” next to the little black screw that allows me to remove the rear cover. One nice thing; the fury this engendered means I will remember this silly screw for the rest of my life. No need for the manual anymore.



Once I got the MM600 fired up, I was delighted by the large display (Figure 9). I also was impressed that it came with a type-K thermocouple. It’s not true-RMS, but it only cost $71.66 including tax. I was later burned by this meter when I was troubleshooting my Fisher Scientific ultrasonic cleaner.



This meter cannot measure a megaohm. That cost me an hour, until I got out the Fluke meter and saw the 1M resistor was not open-circuit. Another thing with this cheaper meter is the quality of the probes. The MM600 probes on the right were OK, but obviously cheaper. The Fluke probes I have in the meter here just feel and look better, as they should, for 7 times the price. The MM600 puts the “OFF” location in the center of the knob rotation. The Fluke 187 and 189 put the off location at the full counterclockwise location. I can see the rational for both choices. The MM600 takes fewer clicks to get to any measurement. The dc volts and 10 amperes ranges just take one click. The Fluke user interface choice means you don’t have to look at the meter to find “OFF,” you just crank the knob all the way to the left, where “OFF” is supposed to be. I assume programmers were involved since the arbitrary “improvement” means there is no standard user interface and now you have to look at your meter to be sure what brand it is before turning it off. At least hardware or mechanical engineers designed the probes. The banana plugs and jacks inter-operate between the two brands, hallelujah.

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