I plan on installing completely separate supplies (xfmr, regs, etc.) for each
meter.
Way, way overkill, man. It sounds to me like you're going to be
building 3 power supplies to support your upgraded existing power
supply.
I've not decided on LED or LCD.
Each meter will do double duty as V and I meter (via toggle switch).
Watch out for voltage drop across toggle switch and shunt, and now
you'll have to do current shunts too.
My problem is understanding my need for accuracy.
The outputs are 0-25/0-25/0-16. So my presumptions are:
- a 3-1/2 digit meter that is wired for 20v max will give 2 decimal places
of accuracy; wired for 200v max it will give 1 decimal place of accuracy.
- a 4-plus digit meter will give an additional digit of accuracy under these
conditions.
So I must decide if 0.1v accuracy is OK for 2 of the outputs.
Yeah, you're the one who has to decide that.
What's the resolution/accuracy you got from the old analog meters?
0.1V is 0.4% of your 25V full-scale, and that's pretty good for a big
old analog meter with a mirrored scale. More typical accuracies for a
small front-of-power-supply analog meter is 2 or 3%.
And don't confuse resolution with accuracy. You'll have to be using
better-than-1-percent resistors (probably just go to 0.1% resistors)
in your dividers and shunts etc.
This is beginning to sound more like an exercise in specmanship (well,
not even that, more like an exercise in how many digits can we
display) than any actual utility.
If you're getting the impression that I actually prefer analog meters
for many quantities, you'd be correct! Do you really need to know the
current to a fraction of a percent, or just see if it's drawing any at
all or pegging the needle? Some of us know exactly what sort of
overload it is by not looking at the analog meter, but by the noise it
makes when it hits the peg!
Tim.