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G

George Shaw

Jan 1, 1970
0
Folks

I am looking for ideas for the following, and of course though some of
you would have a few ideas.

I need to attach a Data Logger device to a series of relays. There is
not always spare contacts on the relays and I can NOT add wires to the
existing relays. The logger simply records change of state form say
de-energised to energised (open-closed, picked-dropped, No - Nc, power
on power off) switching at the moment via the negative wetting voltage
supplying spare contacts that mirror the actions of the ones being
monitored.

I am looking for a Cheap induction type clamp on device (up to 38
channels need to be monitored so each logger will require 38 of the
devices). The inputs to the logger are + and - with logging taking
place when a voltage is applied or dropped (+ V detected = Bit 1, - V
detected bit 0 change from bit 1 to 0 = change in state). I am happy
to build such devices or to purchase if cost is within reason.

Any ideas or products/designs circuits welcome.
 
H

Harry Bloomfield

Jan 1, 1970
0
|
| I am looking for a Cheap induction type clamp on device (up to 38
| channels need to be monitored so each logger will require 38 of the
| devices). The inputs to the logger are + and - with logging taking
| place when a voltage is applied or dropped (+ V detected = Bit 1, - V
| detected bit 0 change from bit 1 to 0 = change in state). I am happy
| to build such devices or to purchase if cost is within reason.
|
| Any ideas or products/designs circuits welcome.
|
|

Have you considered adding an Hall Effect switch alongside the coil of
each relay, as a means of detecting whether each is energised?



--
Regards,
Harry (M1BYT)...

Remove the 'NOSPAM' in my email address to reply.

Free Amateur Radio Courses:-
http://www.ukradioamateur.org
 
D

daestrom

Jan 1, 1970
0
George Shaw said:
On Sat, 6 Sep 2003 10:41:20 +0100, Harry Bloomfield



The problem is that each relay is fitted with NC and NO (front & back)
contacts and I need to monitor the state of each, yep I know that the
contacts would change state together and that the coil would be in an
energised or de-energised state but I need to prove each contact
(legal requirement) I don't even think I can get close enough to the
coil to enable detection with a Hall Effect and if increased in
sensitivity there is much greater possibility of interference from
nearby coils. The coils/relays are DC and the current carried by each
contact is DC.

Hmmm... sounds like a tough one.

How much DC current through the contacts? Maybe you could just measure the
current in the contact circuit somehow? That could prove the contacts and
maybe even some other components?

daestrom
 
H

Harry Bloomfield

Jan 1, 1970
0
| Hi Harry
|
|
| The problem is that each relay is fitted with NC and NO (front & back)
| contacts and I need to monitor the state of each, yep I know that the
| contacts would change state together and that the coil would be in an
| energised or de-energised state but I need to prove each contact
| (legal requirement) I don't even think I can get close enough to the
| coil to enable detection with a Hall Effect and if increased in
| sensitivity there is much greater possibility of interference from
| nearby coils. The coils/relays are DC and the current carried by each
| contact is DC.
|
|
|

Hmmm, a tricky one....

If you must prove the position of each individual contact, then there
are still ways it can be done. Assuming each contact would have a
steady DC voltage across it, or that a DC level would change on the
contact opening and closing, then an op-amp circuit could be used to
detect that changed voltage.

Assuming a reasonable level of current flow and a small voltage drop
would not matter, then a small amount of resistance in series with a
contact would produce a voltage across that resistor. Even a PCB track
may have enough resistance. Test for voltage across it, voltage there
indicates the contact is closed. This again could be done with an op-
amp.

Another possible way, assuming good isolation between each circuit,
would be to feed a small source of AC onto one contact and then see if
it comes out from the other. A capacitor on the input to the contact,
plus one on the output contact, would filter off the DC component.
Either an op-amp or a 555 timer could then be set up to see if the AC
is passing through the individual contact set.

If one end of the contacts were common to each other, then feed AC in
onto that common. Then just check for AC on the output contacts.

Without a great deal more information, I can only stab in the dark with
my suggestions, but I don't wish to do more than suggest generalised
solutions or I will be doing the job for you.

--
Regards,
Harry (M1BYT)...

Remove the 'NOSPAM' in my email address to reply.

Free Amateur Radio Courses:-
http://www.ukradioamateur.org
 
G

George Shaw

Jan 1, 1970
0
| Hi Harry
|
|

Hmmm, a tricky one....


Harry I will email you direct later this week to explain in more
detail. AC feeding is OUT (the relays are AC imunue but we would not
be allowed by RailTrack law to introduce it or anything else into the
circuit).

The ONLY available way is to detect the wires which carry on average
DC but yes some do carry AC.
 
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