Cliff, this is an interesting situation. The engineer was trying to keep track of the different grounds, but the software didn't know that. What he did made sense, but then again, so did what the software did.
From a design standpoint, separating anlog, digital, and different power supply gnd/returns is vital to the integrity of the circuit and isolation from noise. Measuring voltage on a 12V line requires you connect the scope-probe ground to the 12V return, likewise the 5V and 24V busses. If the designer isolated those lines, there is good reason to believe they should stay isolated. I can't argue with your success, but I'd guess that the problems you were trying to fix still exist and will evidence themselves in degraded performance and/or damaged components.
This can be a bit of a pain with some software and and the typical solution is to create a component that is nothing more than copper attaching the grounds. I had an engineer that created such a part, and placed the copper joining all the grounds on a new layer. This was a great idea, but after he left the company the next engineer didn't know that the Gerber files needed to have that extra layer included. That was a darn expensive mistake.
Many many years ago (when I was young and wore a uniform - never mind what color, thats classified) I had to troubleshoot a fault which was caused when a technician mistakenly swapped the ground and neutral lines on an isolating transformer.
We were testing voltages with a multimeter, and all the voltages checked out (no surprise, the multimeter is floating). It was only when we put a scope on the voltage line that we saw the problem. That taught me a lesson about measuring voltages.
I don't blame the tech who swapped the wires, though. They were old and covered in dust and grime, it wasn't so easy to see the different colors. Only people who never do any work never make mistakes.
Very interesting post. Some years ago I took on the responsibility of comparing a UL standard for domestic cooking products with a comparable IEC standard describing the same category of appliances. I was somewhat surprised to find many symbols vary considerably and there is no "universal" standard defining nomenclature. Even the "caution", "warning", "hazard" symbols are different depending upon application. Again--good post.
For those of you that use Altium Designer, NetTie is the appropriate object to use.
You create a schematic part of two pins shorted together (with a PCB part with two pads shorted together) then designate the part as a net tie. This allows two nets to be tied with this one part. The PCB then allows the two nets to exist seperately but be tied with the net tie part and then pass DRC checks.
Keeping the different grounds isolated from each other is often required for optimum performance. But this generally requires a single point connection for all the return current. It should be assumed a different ground is indeed "a different ground".
What is the most common resistor value in the world? Zero ohms! (at least a few years ago, according to a resistor manufacturer)
Used for jumping over traces (reduction of layers) and connecting optional and not so optional (like grounds) wiring nets.
Drives me crazy when a CAD program will allow merging of different nets into a common net without some distinction (like a zero ohm resistor separating them). Otherwise.. why use different names? It just creates confusion... even if it makes design re-use easier (combining pages from different designs when creating a new design).
Linear guides are one of the most important components required for the design of automated or computer-controlled equipment. Aluminum profile extrusions, used for these guides, can enable designed-in functional features.
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