Door Position Switches (DPS) For Access Control Tutorial

Author: Brian Rhodes, Published on Mar 05, 2018

Door position switches do not get enough respect. They solve a major problem of access control systems yet are frequently ignored or forgotten.

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Type *********

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Comments (11)

I agree they don't get enough respect, it still amazes me how many times we run into an installation with no door contacts, they provide critical information to an access control system.

REX's would be the next in line needing a little more respect, it's important to be able to differentiate between a valid exit and a door force.

You may just want to mention two other things:

While I understand not everyone works in secure detention facilities, there should be a passing mention how different (and big of a PITA) those kind of door switches can be.

It might also be good to point out why you would want to use a DPDT contact in certain circumstances.

I strongly agree to the recommendation that the use of DPS is the best practice inoder to monitor whether the door is open or closed.

There is no exaggeration in suggesting that DPS don't get enough respect as i have just pointed out the missing DPS in the current on going installation.

I just want to state that the knowledge acquired from IPVM is bearing the fruits.

I agree with

For Double Pole-Double Throw contacts, would those be useful in normally open (NO) circumstances?

Yes. The double throw means it can be normally open or normally closed. If it were a double pull, single throw it would only be normally open or normally closed not both; although I don't think I've ever seen a door contact that is DPST.

The double pull means there are 2 independent circuits that can see the state change. It's important to note that while both circuits are tied together and will see the same state change, they are independent when it comes to being normally open or normally closed. Also because they are eclectically separate they can both have their own resistors in the circuits so one system can be NO with 1k Ohm in parallel and the other could be NC with 100 Ohm in series.

You guys mean double-pole, not poll or pull, right? :)

Yes, double pole is correct. I'm not sure why I wrote 'pull' or if it autocorrected to that, but I've changed it now.

I can't edit mine for some reason.

I disagree about the “Magnetic 'Bullet' Style” being hard to align. We use these 90% of the time (we do a lot of access control) and we don’t find this to be a issue.

It is not difficult if you install them regularly, like yourself, or if you have experience recessing door contacts in intrusion work, but for a novice getting the top and bottom halves lined up can be tough.

Also, making basic alignment measurements can be a challenge if the door itself is out of square or unaligned with the frame.

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