14 Jan
2006
14 Jan
'06
2:22 p.m.
The worst high voltage design I have ever seen was a
Fluke
Digital Voltmeter that I used to have. I think it was an 8300.
It used Nixie displays, and the high voltage for the Nixie tubes
ran on a trace that just weaved it's way across the circuit board
(with feedthroughs, etc,) without isolation or anything about it
to differentiate it from other traces. The board was not
solder-masked, so the metal was bare and exposed. Adjacent
tracks were low-level signal lines.
Well, the supply yo nixie tubes is likely to be a lot less deadly than
mains. I am thinking of the HP9815 calculator. That has a Panaplex
display, the HV for that comes from the PSU/printer board to the
keyboard/display interface via one wire of a 24 pin ribbon cable. All the
other pins are TTL level signals. And HV on exposed components on both
boarrds.
The worst I've seen (as it made me leap) was the PSU from a Tektronix
terminal (I forget he model number, but it was a colour, raster-scan
one). This was a little SMPSU in a metal can. Unfortunately, there was no
bleeded resistor on the mains smoothing capacitors. If the startup
resistor went open-circuit, the capcitors had no way to discharge. And
the way into the supply was to undo a couple of screws and slide the PCB
out. If you didn't realise the capcitors were likely to still be charged,
you would most likely accidentally touch the mains smoothing capacitors
with painful results.
Does anybody else here appreciate old Fluke gear? My
newest
Yes. OK, I've got a new-ish Fluke too (original 85) that I use all the
time too.
I have one of their data loggers, a 2240 or something like that. It's
controlled by a pair of 4040s, one for the main control, one to drive the
paper tape output. I have only one 10 channel input board (but I do have
the temperature-compensated input connector block on it), the
high-resolution ADC (of course this is isolated from ground, all the
digital inputs/outputs to it are opto-isolated), the internal printer,
and so on. It's very well made, and a joy to use.
-tony