[RadioTelescope] Suggestions for safe operation

Harry McNally harrymc at decisions-and-designs.com.au
Wed Mar 31 11:01:29 WST 2010


Hello

We made good progress last night evaluating the mount control box and stepper
motors; lathiat's email summarises it "It works". (Email posted on ucc list atm).

The wiring is robust and secure but I think is designed for the box to remain
closed while in a powered state unless being manually operated by Physics
technical staff. Given that people will want to examine and operate the system
with the cover open, I'd like to suggest ways to make the system safe for any
UCCan (regardless of experience around mains power) to be able to hack on it.

There are two mains inputs, one for the large stepper motor power supply and a
second for the +5, +12, and -12 volt UWA built interface board supply.

In order to remotely power the system, a relay on the UWA built interface
board controls the power (by switching the active mains wire) to the large
stepper motor power supply. Two buttons on the UWA interface board allow the
supply to be manually powered on and off and I assume the remote (parallel
port) input provides a similar mechanism for when the dish is unattended.

What all this means is that mains power is connected to the UWA interface
board at a terminal block which is a potential point of contact for people
working within the live mount control box.

There is also another exposed active mains termination on the terminal strips
that the stepper motors are connected to.

I'd like to suggest:

- that the large stepper motor supply is controlled by a sealed (diecast?) box
with a fused IEC connector and containing an opto-isolated solid state relay
and bolted to the power supply chassis.
See:
https://www.soanarplus.com/getProductWebDetails.do?prodId=SY4084
https://www.soanarplus.com/getProductWebDetails.do?prodId=PP4004
or
https://www.soanarplus.com/getProductWebDetails.do?prodId=PP4003

The relay requires a 4 to 32 volt (possibly 5 volt logic) level applied to the
opto-isolated input to "close" the mains terminals. Initially the UWA
interface board could be modified to connect the existing relay drive circuit
to the terminal block presently carrying the 240 volt mains wires. The solid
state relay control could then be wired to that terminal block.

- that a quad switched power point is installed inside the box and that a
mains cable terminates behind that and feeds out of the cabinet through a
sealing and cable restraint gland either at the rear or side of the cabinet
(so the cabinet can still be stood on the bench).
See:
http://au.farnell.com/lapp-kabel/52105450/gland-viton-m16-5-8-6-8mm/dp/1691684

- that any power supplies for the UWA interface board or a replacement are
provided by wall-wart power supplies so there is no access to mains wiring
anywhere in the box; hence the quad power point.

- that a perspex cover is installed on the larger stepper motor power supply
around the filter capacitors to prevent contact with the ~100V DC supply power
at the capacitor terminals.

- that a perspex cover is installed above the stepper motor driver modules to
prevent screws or other conductive parts from dropping onto the module PCB or
power MOSFETs; allowing for air flow for heat off the modules.

Once those modifications are in place and have been inspected and/or tested by
UWA safety people, I think anyone can gleefully (and safely) hack on the
control box.

All the best
Harry




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