How to wire two PIR motion sensors together to activate only on double trigger ?

[Paul N]

Dear All,

I have a very old Scantronic alarm system that unlike modern systems does not detect resistance values (no resistors in PIRs or in zones) but activates when the Normally Closed contacts become open.
The PIRs are wired with 4 core +ve -ve NC and Com
Is it possible to wire two PIRs together so that the panel doesn't activate unless both PIRs become open ?

Is it as simple as connecting the NC and Com from PIR 1 to PIR 2 so that the trigger works 'in series" or does Connecting NC PIR 1 to Com in PR 2 do the trick ?
Or ......
Many thanks for your help, I can't seem to get my head round this !!!

 

[Avo Mk8]

Dear All,

I have a very old Scantronic alarm system that unlike modern systems does not detect resistance values (no resistors in PIRs or in zones) but activates when the Normally Closed contacts become open.
The PIRs are wired with 4 core +ve -ve NC and Com
Is it possible to wire two PIRs together so that the panel doesn't activate unless both PIRs become open ?

Is it as simple as connecting the NC and Com from PIR 1 to PIR 2 so that the trigger works 'in series" or does Connecting NC PIR 1 to Com in PR 2 do the trick ?
Or ......
Many thanks for your help, I can't seem to get my head round this !!!

An NC switch in series with another NC switch gives the "OR" function for your situation
An NC switch in parallel with another NC switch gives the "AND" function.

So assuming those PIR contacts open when someone walks by, then you need to wire PIR 1 contacts across PIR 2 contacts, ie Com to Com and NC to NC, and feed that parallel combination to the panel.

 

[Paul N]

An NC switch in series with another NC switch gives the "OR" function for your situation
An NC switch in parallel with another NC switch gives the "AND" function.

So assuming those PIR contacts open when someone walks by, then you need to wire PIR 1 contacts across PIR 2 contacts, ie Com to Com and NC to NC, and feed that parallel combination to the panel.

Dear Avo,

Thank you so much !! I had looked up everywhere on the internet and couldn't find the answer.
The way you described it is perfect and logical - I was tying myself up in all sorts of knots trying to work out how the relays and the current would run !!!!

Thank you once again.

Many thanks
Paul

 

[mainline]

Dear All,

I have a very old Scantronic alarm system that unlike modern systems does not detect resistance values (no resistors in PIRs or in zones) but activates when the Normally Closed contacts become open.
The PIRs are wired with 4 core +ve -ve NC and Com
Is it possible to wire two PIRs together so that the panel doesn't activate unless both PIRs become open ?

Is it as simple as connecting the NC and Com from PIR 1 to PIR 2 so that the trigger works 'in series" or does Connecting NC PIR 1 to Com in PR 2 do the trick ?
Or ......
Many thanks for your help, I can't seem to get my head round this !!!

Commonly known as double knock, some pirs have a latch on time delay for a few seconds, giving time for the 2nd one to activate .