Replacing DSC with Elk - EoLR Questions

PLCGuy

Member
This is our first attempt at an alarm system (we primarily do industrial control and cyber security systems) and we have run into an interesting issue out of the gate. The customer has an existing DSC system with about 30 zones. We are replacing the DSC with an Elk, along with automating the lighting and a cistern water management system. So far, so good...
 
The issue is that it appears that the Elk uses 2200 ohm EoLRs, but the DSC was installed with 5600 ohm resistors through out the building. The thought of replacing all 30 zone's EoLRs is less than appealing, as the sensors are not easily accessible in many locations. Any suggestions?
 
Thanks
 
 
Better start cutting and patching!  If this is a residential installation, I would remove the old EOLRs in the process. 
 
The only other option isn't appealing either...getting low current TTL relays and wiring the zone pair to the trigger and the dry contacts to the M1, increasing the amount of hardware that can fail.
 
Time to start locating those EOLR's.
 
Try a 3300 ohm EOLR in parallel at the panel end. That will drop the resistance down to ~ 2k and should allow the Elk to work. Of course that defeats the EOLR circuit and if a zone fails open not sure what the Elk would do but for a house it should work.
 
Definitely something to discuss with your customer - because as just said above, it's definitely possible to "do the math" and rig it to get you the correct resistance again - but should there be a failure of some sort, it will definitely do screwy things or go unnoticed.  Many people do this though to avoid all the work.
 
Otherwise dig out a sensor and see what you're up against - and are you 100% sure the resistor is EOL? Many people did shortcut and put them at the panel... or sometimes it will be built into the contact so the whole contact would need to be replaced.  I'd at least dig out one and see before making a final decision.
 
srodgers said:
Try a 3300 ohm EOLR in parallel at the panel end. That will drop the resistance down to ~ 2k and should allow the Elk to work. Of course that defeats the EOLR circuit and if a zone fails open not sure what the Elk would do but for a house it should work.
This may will not work as it should give you around 8.7 volts with the sensor opened. and the usual 7 or so volts with the sensor in the closed position.  The important thing is to look at the voltage differential between the status of normal and violated to insure you have a comfortable margin.
 
Of course you will loose the 'benefit' of monitoring the lines that a typical EOL scenario will give you as srodgers stated.
 
BraveSirRobbin said:
This may work as it should give you around 11 volts with the sensor opened.
 
Please check your math.  I get 8.3 volts which is NOT sufficient for an alarm indication.
 
jpmargis said:
Please check your math.  I get 8.3 volts which is NOT sufficient for an alarm indication.
Yes, you are correct.  Edited my post above.  Thanks!
 
Looks like the only real solution is to go ahead and dig out the old EOL's :(
 
I think you guys missed the key point in the original post that he already had 5600 ohm EOLR. Adding another 3300 in parallel makes the EOLR resistance seen at the panel 2076 ohm which is close enough and within the tolerable range for the Elk to see it as a normal EOLR circuit. The EOLR function does not work but a NO zone will function correctly. Just tried it with a 5600 and 3300 ohm resitor in parallel across an unused zone.

But this not really a solution but the numbers do work.
 
You missed the point!  It doesn't work on a NC zone because you can never achieve the spec'd alarm voltage of 8.8 volts with the 3300 ohm "EOLR #2" still in the circuit!!  The numbers DO NOT work.
 
I guess it would help if the OP told us NO or NC for the existing installation.
 
It does not work. Academically and mathmatically it works, however when the zone is open, you have a high resistance fault, which is introducing another issue. Panels don't look for resistances on a 3 state circuit...voltages and determine what is going on within those 3 states....not to mention trouble conditions.
srodgers said:
I think you guys missed the key point in the original post that he already had 5600 ohm EOLR. Adding another 3300 in parallel makes the EOLR resistance seen at the panel 2076 ohm which is close enough and within the tolerable range for the Elk to see it as a normal EOLR circuit. The EOLR function does not work but a NO zone will function correctly. Just tried it with a 5600 and 3300 ohm resitor in parallel across an unused zone.

But this not really a solution but the numbers do work.
 
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