[navajocont]

I need to install a 12 volt system, to alert by alarm, when both security door are open at the same time.

1. I have a 2 door airlock.

2. A light is on in the airlock.

3. The light remains on when one door is open.

What I need is an alarm to sound when both doors are open ?

I haven't started the project yet, I would be grateful for any help.

List of materials and a diagram would be superb.

Many thanks in advance for any help.

Best regards

Paul,, (Hampshire, UK)

 

[great68]

This would be a simple circuit involving a power supply, magnetic door contacts , a few relays and some buzzers. You should be able to work it out if your doing the job.

 

[wildleg]

sounds like a homework question

 

[LARMGUY]

They make normally open contacts. Easy peasy.

 

[bobzzz]

First time poster long time reader.

If you need an alarm to go off only when both doors are open, why don`t you use 2 micro switches in series to an alarm? It is very basic electrics and I do not think you will need a diagram for that.

 

[gnuuser]

They make normally open contacts. Easy peasy.

for a dual door activation alarm 2 nc switches wired in series with a relay to energize the alarm.
with a lead to the lights off of each switch(if 12 volt light)
if 110 volt lights you will need relays for each light and a relay for the alarm horn
same principle as wiring e stop switches
contacts are open when the doors are closed and switch is depressed
either way its a simple diagram and circuit

oops forgot its a uk forums (dpst relay or contactors)
still its a simple circuit

 

[gnuuser]

for a dual door activation alarm 2 nc switches wired in series with a relay to energize the alarm.
with a lead to the lights off of each switch(if 12 volt light)
if 110 volt lights you will need relays for each light and a relay for the alarm horn
same principle as wiring e stop switches
contacts are open when the doors are closed and switch is depressed
either way its a simple diagram and circuit

oops forgot its a uk forums (dpst relay or contactors)
still its a simple circuit

Another way to do it would be easier would be to use dual micro switches.
Wiring the supply for the lights parallel and the alarm horn in series.

 

[gnuuser]

i actually have a diagram somewhere in my office for one i did about 5 years ago
2 ice cube relays, tow micro switches; 4 indicator lamps, and battery pack/
dc power supply
simple circuits but if done right impresses the hell out of clients:laughing:

if this is a homework question though it wouldn't be fair to post it

 

[gnuuser]

the drawing isn't very neat but close enough
In this drawing instead of using blueprint schematic symbols.
I used a pictorial drawing from an ice cube relay (Potter & Brumfield krpa-11dg-12).
The blue highlighted lines are connected to the common terminals on the micro switches and the common terminals #1 0n both ice cubes.
the lines highlighted orange show the present path of the current after the micro switches. (both doors in closed position so both door closed lamps are lit)
the red/black lines highlighted yellow show the series circuit that will allow the horn to sound if both doors are open.
inactive circuits in present state are not highlighted

using 4 lamps with this set up serves two purposes:
the state of the doors will be visible at a glance whether they are closed or open.
also if for any reason that the power is cut example accidental severing wire at door or tampering the door closed lamp will not be lit
if both lamps (door closed)are not lit then power has been interrupted before the micro-switch common junction or at battery
either situation would warrant an investigation by security.

as stated in the earlier post this is a simple but effective design
using 12 or 24 volt as a control voltage you would be able to switch
contactors for higher voltage alarm devices

 

[gnuuser]

hope we didn't scare the OP away