As important as the quality of an analog meter's movement is to accuracy, equally important -- especially for high accuracy -- is the artwork on the meter's faceplate.
For the past couple of months, I've been working with Max Maxfield on the analog meter problems and design challenges pertaining to his Inamorata Prognostication Engine, Ultra-Macho Prognostication Engine, and Vetinari Clock projects.
As you may have read in columns like The Solution to Your Analog Meter Woes, Analog Faceplate Design Decisions: Art or Science?, and Yummy Scrummy Antique Analog Meter Faceplates, Max and I have been in almost constant daily communication, by either email or phone. During our conversations, we have had a blast talking about various aspects of these meters, such as the fact that some meter movements deflect 100 degrees, while others deflect only 90 degrees. This point took Max by surprise after he incorrectly had his graphics guru Denis create the Vetinari Clock's "Hours" faceplate assuming a 100-degree movement when the meter was designed to operate over a 90-degree swing. Fortunately, we managed to make the meter's movement match the faceplate.
As part of this, I've been telling Max about some of the meters we make and repair here at Instrument Meter Specialties (IMS). Take the small Triplett .5E edgewise meter that goes in an older aircraft. These meters read "GOOD" in a green area in the middle, with red areas on either side. They would cost hundreds of dollars when the aircraft were created, but they now sell for thousands. The thing is that the planes were certified with these meters, which are FAA approved, so no substitutions are allowed.
Another job I was telling Max about involved an upgrade on some meters that go in a nuclear power plant. These meters were stockpiled when the plant was commissioned. As they started to reach their end of life, replacements were brought online, but they were failing their 0.6% calibration tolerance, and we had to work our magic on them. (I'll describe how we achieved the required accuracy in my next column.)
We do a lot of work on the older Hickok tube tester meters. We've also experienced an analog meter resurgence in the recording industry. In fact, we make several different meters for old audio compressors from companies/products such as Fairchild, Gates Sta-Level, and Federal TV. Being a custom meter shop with the ability to make complicated artworks means we can satisfy just about any meter-related requirement, so long as the parts are available.
Based on his projects, the topic Max and I have spent the most time discussing by far has been the creation of artworks (faceplates) for the meters. A lot of work goes into analog meter movements and artworks. This tends to be why new meters can cost a lot of money. The parts can be as small as those in Swiss watches, and it takes skilled hands to make a really good meter movement. This is why we always have our trusty microscope at the ready. Even meters with a "linear scale" only have movements rated to be within 1-2% of the full scale input at any given point of the scale. The trick to this "linearity" is accurately placing the coil within the magnetic field and making sure that nothing affects the spring constant, like friction caused by two spring turns rubbing against each other or deformations such as creases in the spring. That said, as important as the meter's quality is to accuracy, equally important -- especially for high accuracy -- is the meter's artwork.
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