I recently purchased a replacement explosive gas sensor for a storage area and realized that the meter had been very neatly relabeled with the appropriate text. They were buying 0 - 20 ma gauges and then affixing new text on the meter faces for the application at hand.
One thing I'd vaguely considered was to sand the faceplate down (using very fine sandpaper), spray-paint it white, and then add the new annotations by hand using a very fine indelible marker. But the more I think about this, the more I think the result would look absolutely horrible
But more realistically Victorian! In my blog Touring as an Engineer, I mention the Pitt-Rivers Museum where the labels on the exhibits are either handwritten or written with a typewriter with a rather grungy ribbon.
ALL D'Arsonval (moving coil) meters are the best type, and the basic design is ALWAYS a DC current meter. Many of these have a movement wiith a full-scale range of either 50uaDC (the expensive ones) or 1maDC. These can be made to display other functions or ranges by connecting either a shunt resistor (for higher FS current) or series resistor (multiplier) to change to a DC voltmater. For AC, the meter may be a moving-vane (e.g. Shurite type, usually relatively cheap) design which will work for AC or DC (although scale factor may be off), or uses a rectifier (typically bridge) along with a multipler or shunt. VERY often, the shunt, multipler, and/or rectifier is EXTERNAL, so you CAN'T go by the faceplate in determining the meter configuration! It's pretty easy to tell, thpough, with a DC power supply, some resistors, and a multimeter. Assume it's a "naked" DC milli/micro-ammeter, connect the PSU, a suitable current-limiting resistor, and the multimeter (in ammeter mode) in series and see what the meter does when the PSU is turned on. Ther rest of the process (and how to calculate appropriate shunt/multiplier values) is left as an exercise for the student!
PS: examining the photo of the disassembled meter, it has an internal shunt THAT CAN BE REMOVED. That would restore the basic movement range etc. so you can use it! Same for "voltmeters" except the multiplier is often external; if it is internal, it's also easily removable.
Also, nearly all faceplates are symmetric; thus no need to scrape. Just flip it over and paint! I've used that trick many times. If you have an old drafting tool/ pen set, the compass is terrific for draing the scale arc (if you can find some India ink.....). I have a couple of sets (including one older than I am).
What are the engineering and design challenges in creating successful IoT devices? These devices are usually small, resource-constrained electronics designed to sense, collect, send, and/or interpret data. Some of the devices need to be smart enough to act upon data in real time, 24/7. Are the design challenges the same as with embedded systems, but with a little developer- and IT-skills added in? What do engineers need to know? Rick Merritt talks with two experts about the tools and best options for designing IoT devices in 2016. Specifically the guests will discuss sensors, security, and lessons from IoT deployments.