[Test-Equipment] Ideas ?

Sun, 7 Sep 2003 09:27:51 +1200

George
 I think Hall effect devices are still the best bet, but you should contact
LEM and see if they have any small 'permanent clamp-on devices- they
definitely DO have these but  the only ones I am aware of are in the larger
sizes and probably too big for your application- these are the sort of  CTs
that are fitted to busbars etc.
But they may have smaller ones -otherwise small basic Hall devices literally
glued onto the cables should do the trick- you will probably have to do a
bit more of your own interface electronics in this case though.

Dave Brown
ZL3FJ
Christchurch, NZ

----- Original Message ----- 
From: "George Shaw" <[email protected]>
To: <[email protected]>
Sent: Saturday, September 06, 2003 11:53 PM
Subject: RE: [Test-Equipment] Ideas ?

I thank you for the ideas so far but let me explain a bit further. The
relays are all British Rail specification relays in an interlocking relay
room controlling signals and points for Belfast Central Station and beyond.
We can NOT break any cables to make any sort of connection nor can we attach
direct to the coils or cases of the relays. What we have done so far is to
use a spare contact (front or back NO or NC) that mimics the contacts we are
monitoring feeding it with 24V DC and logging the change in state from open
to closed (+24V present to 0V present at date logger channel input) the
relays are all DC.

We do not always have a spare contact and are not allowed to connect
anything into the lines that carry any control signals to the network. The
only way we can do this is to attach some sort of device that will clip onto
existing cable somewhat like a clamp meter induction clamp. We only need
this device to:

1. Sense the presence or not of a current (DC) and switch a 1v to 24V
current to the data logger. (+V = Bit 1 ON - 0V = Bit 0 OFF)

2. Allow non-contact or non-intrusion connection to the cable.

4. Be economic enough to allow several hundred to be used, the idea being to
attach them and leave in place. Or at least 38 per relay room at a time on a
semi-permanent bases.

5. Themselves NOT to introduce any AC or any interference with the cables
they attach to.

--
George Shaw MI3GTO

" Any Sufficiently Advanced Technology
is Indistinguishable from Magic"
                          ---Arthur C. Clarke

Mobile: +44 (0) 7740 361 163
Email: [email protected]
Fax & Voicemail: +44 (0) 871 242 9183

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