This is the problem:
Many industrial devices powered by 24 volts DC; PLCs computers, etc have
specifications which limit the number of volts which DC Negative,"M"
common, can be away from frame ground. If you don't tie the 0V
terminal on the DC power supply to frame ground, you have no idea how
far "M" is from frame ground since it is floating.
I would not tie the 0V terminal of a 5 volt power supply to frame ground
unless it is required.
For instance, a 5 volt power supply powering Mesa cards. I would leave
that off frame ground unless you find that it must be referenced to
frame ground via debugging.
I once blew a comm port on a USB to RS232 converter when I was
programming an ungrounded 24 volt PLC system. The 0V terminal on the
PLC was not close to absolute ground so the signal ground on the PLC
RS232 connector was also not near absolute ground. My laptop was
connected via a grounded power supply. When I plugged into the PLC
with the RS232 port cable, current flowed from the control systems
ground into the RS232 to USB adapter, through the shielded USB cable and
into the frame ground on the PC which was of course was connected to the
AC power ground. Fortunately the RS232 to USB adapter took the hit and
my laptop was ok. It wasn't hard to figure out what happened as the
computer rebooted when I plugged in the cable. A bad sign for sure!
I obtained another RS232 to USB adapter and programmed the PLC with the
laptop while running off battery power (the Laptop was isolated from
absolute ground) since it was not plugged in via the AC power supply.
Here are some things to read:
https://control.com/thread/1026164262
http://forums.mrplc.com/index.php?/topic/15175-ground-the-24vdc-power-supply-common/
Dave
On 7/13/2018 12:24 PM, Roland Jollivet wrote:
> That's pretty much standard these days.
I'm not making this stuff up. That's how its done.
So which is it? Connect Gnd to 0VDC, or not?
I've pulled apart quite a lot of industrial plotters, printers and I've
Never seen 0VDC connected to Gnd. Same with robots, Injection moulding
machines.
All frame metal parts are quite interconnected, sure, and Grounded, but all
electronics has it's own power system.
I don't understand the desire to connect two lines together because they
'seem' to be of the same magnitude. 0VDC is Not equal to Gnd
Many systems will have multiple 5V power lines, heavy, light, designated.
Do you want to link all those up too?
On 13 July 2018 at 18:05, andy pugh <bodge...@gmail.com> wrote:
On 13 July 2018 at 16:52, Dave Cole <linuxcncro...@gmail.com> wrote:
That's pretty much standard these days.
I'm not making this stuff up. That's how its done.
I think that there is still some confusion out there. I used to work
for a company making specialist test equipment (brake dynos, motor /
pump testers, that sort of thing).
Our electricians were convinced that everything needed an yellow/green
earth connection. Every panel for the control cabinet, the doors, the
individual devices bolted to the machine bed. We would spend ages
making things look nice and painting them, and then they would come
back festooned with stripy wires and with a hole drilled in every
separate metal part for the earth stud.
--
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916
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