|12" iGaging AccuRemote next to DigiMag scales|
Recently iGaging has introduced a new Stainless Steel model of their “Remote Readout” digital scales. The new “AccuRemote Digital Readout” scales are supposedly much more accurate and robust than the older DigiMag model, making them a good candidate for a hobby DRO setup. I’ve been getting emails from people wondering if these scales are compatible with the TouchDRO application (or more accurately, TouchDRO Bluetooth Controller), but since I don’t yet own a set, I wasn’t able to confirm this. When a fellow machinistweb.com forum member CaveBob graciously offered to lend his set for a few days, I jumped at the opportunity. Since Bob gave me permission to take one of the scale apart I think it will be helpful to do a side-by-side comparison to see if the scales are really that much better.
|DigiMag display works flawlessly with AccuRemote scales|
First things first: yes, iGaigng DigiMag and iGaging AccuRemote scales are 100% compatible. They send the data using the same 21 bit synchronous protocol with the same 2560 ticks-per-inch resolutions. Since Bob didn’t include the display units I wasn’t able to check the default clock speed or data acquisition frequency but the old “black” display worked just fine with the scale. Using my test setup I was able to push the acquisition frequency to over 60 Hz using 200 KHz clock speed until the scales started experiencing glitches.Both, the Arduino and Launchpad scale controller read the position just fine.
|Both scales use the same part number for the PCB but different revisions|
Removing the cover revealed that both scales use the same model of the circuit board, but the revision appears to have changed from 0.05 to 0.06. I wasn’t able to identify any differences, so it could be a slight difference in the embedded chip or something along those lines.
The differences between the two models is noticeable even at a quick glance. As advertised, the AccuRemote scales use ground stainless steel frames whereas DigiMag’s frames are [extruded] aluminum, anodized on 3 sides. Using my trusty Mitutoyo mike I measured both frames. The stainless steel frame had one spot that was about 0.0002” narrower than the rest while my 35” aluminum scaled had two spots that had over 0.003” gouged out of the side. In practice I don’t think this would matter but the AccuRemote frames are definitely much better made and will probably last longer.
|Construction differences are evident even at a quick glance|
A much more important difference can be seen between the two reading heads. The older DigiMag scales’ reading head consists of two plastic halves that contain the main circuit board. AccuRemote, on the other hand, use a machined [stainless] steel bottom. The latter fees very solid and slides very smoothly. In contrast the DigiMag scales feel a bit “grainy” and can be wiggled enough to affect the reading by about 1 thousandth.
|AccuRemote feel much smoother and robust
thanks to the ground frame and machined slider
Once the cover is take off and the controller board removed the differences become even more apparent. The DigiMag head appears to be supported only by the four flat-head screws. The thin piece of copper appears to serve two functions: a grounding strip and a weak gib pressed against the smooth side of the frame by a small spring. In contrast a much thicker brass gib with two small set screws presses the AccuRemote’s frame against the opposite side of the case, creating very solid setup.
|A tiny set screw can be seed in the far corner of the slider|
The differences in construction and build quality between the AccuRemote and DigiMag scales are very noticeable and in my opinion more than justifies the higher price. The new stainless steel frame appear to be ground as opposed to the older extruded aluminum ones. In conjunction with a machine metal reading head body the scales feel smoother and much more solid. If there is indeed a difference in the accuracy between the two models, it would most likely be a result of the improved interface between the reading head and the frame.
At the time of this writing 12” AccuRemote Digital Remote Readout Scale sells for around $60 at Amazon and the 38”-long version is about $50 more. In contrast a 12” DigiMag Scales retail for about half as much, at around $30 and the 35” model can be had for $75 or so.
I’d like to clarify one point that has stirred a small “email storm”: the AccuRemote scales are advertized as “super high accuracy” on some sites, attributing the accuracy and repeatability improvement to the fact that the rule is made of stainless steel. A few readers have made a valid point that SS has lower coefficient of expansion and gave me some flack for not mentioning it. Frankly, I don’t think this is an important factor, and here is why. Aluminum (depending on the alloy) has thermal expension coefficient between 12.8 and 13.2 microinches per Inch-°F whereas stainless steel’s coefficient is around 7.2 (glass is around 5.0). In a context of an average garage this translates to approximately 0.0007” difference in expansion per foot for each 10 °F temperature difference. Assuming that you are dealing with wild temperature swings of 30 °F and are using a 36” scale, the difference in expansion will be around 0.0064” (0.014” vs. 0.0076). Call me crazy, but in a home shop I wouldn't lose sleep over 0.00004% vs. 0.00002% error.