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Water Leak Alarm System using SPDT Relay

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New Member
Hello Everybody
Good Day!!
currently I am working on the leak detection system for one of my project and I want to make it simple instead of making it complicated. I need you advise in order to make this alarm system, Details for leak monitoring panel

1) I am looking for a water leak alarm monitoring panel
2) I want to use the SPDT relay solid state type for logic function
3) This leak monitor will receive signal from a ultrasonic leak sensor
4) The sensor signal will be normally open type
5) The sensor relay voltage is 24 volt DC
6) Hence the Alarm module will work on 24 volt DC power supply
7) This panel will be capable of handling 10 sensors at a time
8) In leak occurs then the signal status will change to NC
9) I want common alarm/buzzer on the alarm model
10) I want common muting switch on the alarm model
11) I want to reset the panel if I push the Muting switch
12) Each sensor will have separate LED indication light
13) Also I want to relay signal to BMS system
I hope I have included all the details and you can help me with guiding ladder logic. I hope ladder logic will be same for 2 or 10 sensors hence i need a kick start from your end.

Thanks in advance.
Parag G


Well-Known Member
Most Helpful Member
I'd like to tell you about a minimalist design I dis back in the 80's. It's probably still working and it's saved a few lives. It was a toxic and Hydrogen shutdown system. It's purpose was to take about 10 inputs, later expnded, indicate the alarm and turn the gasses off. The buzzers belonged in the Toxic gas and Hydrogen portions of the system with a level 1 and level 2. Level 1 just shut down the panel. Level 2 would activate the building fire alarm. The fire alarm would also shut down this panel, but the panel itself would not make any noise. Other sensors also shut down the panel as well as a button on the panel itself and push-buttons at the exits. There were strobes too.

But simply, it was about 10 NO inputs that would latch. The alarm had to be enabled or turned on. Turn on was accomplished with a key switch and a push-button. The key could be removed if we wanted the panel to stay off. Pushing the OFF button or turning the key switch to off would turn the system off. There were alaso three systems that got a selectable enable signal.

Once the panel was on, the system(s) and the gases that were to be used for the experiment were seleected. an NO contact reset the ALARM LOOP and so did a power failure.

The BASIC design was based on BIG 24 VAC relays. DC would have worked too. One SPDT contact was the ALARM LOOP. The other SPDT contact was the individual lamps and the third was a series connection that would break if any alarm went off. So, yep, this one turned off stuff when the panel was in alarm.

The sensors (contact closures) were mostly close by. Tapping two wires together for each sensor electrically latched a relay and indicated it. Label-able Indicators were 24 VAC as well. They were eventually changed to AC/DC LED based.

There was a need to know if the fire alarm was reset and there was a time where we would not be using toxic gas, but they were testing the Fire Alarm. The FAP panel provided SPDT contacts, so I used one to illuminate a "small LED" and the other wold be the "Normal larger indicator" The small LED extinguished in an alarm condition, so we had a way of looking to see if that wire or part of it was continuous and we had a way to know when the FAP panel was reset.

REAL monitored contacts can tell if the wire is open/shorted or in Alarm. This gives you the proverbial "Trouble" alarm.

Power Fail is yet another. In the simplest case, a resistor is placed at the endpoint that is shorted by the alarm contact. So, the alarm system can determine if the wire is continuous to the sensor. You can expand this so you can determine if a sensor wires are shorted, in alarm or open.
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