Confused by EOLR diagram in M1 docs

[benze]

Hi,

Okay - this may seem like a really silly question, but there is something in the M1 docs that is confusing me when it really shouldn't be. I mean, it is a basic principle, and yet, it seems to be completely eluding me right now.

The diagram in question is on pg 9 of the install manual (http://www.elkproducts.com/pdf/M1_Installation&Programming_Manual.pdf).

Basically, it shows the EOLR in parallel with a N/O contact, and in series with a N/C contact. But the state table shows the following:

Resistance		   Armed Condition		 Disarmed Condition
   Short				   Alarm				   Not Ready
   2.2kOhm (EOLR)		  normal				  Ready
   Open					Alarm				   Not Ready

Now, I don't know why this isn't clicking with me right now, but here is my confusion. As far as I know, a N/O contact is one that closes when a mag field is applied. Conversly a N/C contact is one that opens when a mag field is applied.

If one uses a N/O contact, and puts the EOLR in parallel as indicated in the diagram, would the following not occur:
1) Door is ajar therefore contact is open. Panel sees 2.2kOhm as EOLR is in parallel. Considered "Normal/Ready"
state
2) Door is closed therefore contact is closed. Panel sees short. Considered Alarm/Not Ready.

What am I missing / confusing? Or am I just too tired and looking at this diagram late at night not helping?

Thanks for any insight!

Eric

 

[rfdesq]

The "normal" position is when the magnet is doing its thing. Therefore a NO contact is open with the magnet in close proximity. A NC contact is closed with the magnet in close proximity. Does the diagram make sense now?

 

[benze]

The "normal" position is when the magnet is doing its thing. Therefore a NO contact is open with the magnet in close proximity. A NC contact is closed with the magnet in close proximity. Does the diagram make sense now?

Thanks. That was the only way I was able to make that diagram make sense, so I did a little searching on the web, and everything seems to point to a N/O contact being open in the rested/unmagnetized state (ex: http://en.wikipedia.org/wiki/Reed_switch, http://www.explainthatstuff.com/howreedswitcheswork.html, etc).

Is the terminology different here for some reason?

Thanks,

Eric

 

[WayneW]

This is a common confusion. I "think" the security industry thinks this way... they think in terms of a NC or NO circuit, then use switches in their secure (ie with magnet close) state to complete the circuit. Therefore, that switch would get labeled for the type of circuit it is going in, rather than the true type of switch it is.

In the minds of security folks, the magnet being close is "normal"; to switch manufacturers the switch is "normal" when the magnet is away.

 

[benze]

In the minds of security folks, the magnet being close is "normal"; to switch manufacturers the switch is "normal" when the magnet is away.

That's pretty much the conclusion I had come to as well, but what confused me more is the use "Closed Loop" and "Open Loop" circuits in the security world. It would have been much more clear had they specified Closed Loop instead of N/C since N/C is actually a N/O switch....

Anyhow, glad to see that I'm not off my rocker as much as I thought I was last night...

Thanks!

Eric