Re: Beginner question on resistance

On Thu, 22 Mar 2007 21:50:56 -0500, AB <spammenot@xxxxxxxxxx> Gave us:

Now many that post on alarm forums say to limit the series wired
contacts to 3 per transmitter...but other alarm guys say you can add
"as many as you want as long as you don't increase the resistance too
much". There aren't any hard and fast rules it seems. I'm wondering
how you will know how many contacts is too many...when the alarm goes
off?? What is "too much"


That depends on the alarm circuit.

The way to test it is place a potentiometer in that location, and
increase the resistance until you get a trigger event.

Read the resistance of the pot, then read the resistance of a given
length of connection wire, and switches.

As long as you are a good deal (say 20%) below that value in
resistance, you won't cause any false triggers.
.

Relevant Pages

  • Re: Beginner question on resistance
    ... condition) or open (alarm condition). ... The limit depends on how much current the alarm passes through the contacts (and the resistance of their wiring) and at what total voltage drop across that circuit, it decides that some switch is open. ... For instance, if the switch loop is fed with 10 mA and decides that an open condition is indicated at a voltage drop of 2 volts, then the total resistance of the loop and all the switch contacts must drop less than 2 volts while 10 mA passes through them. ... For any reasonable gauge wire, that is a lot of length, but this example is completely hypothetical. ...
    (sci.electronics.basics)
  • Re: Beginner question on resistance
    ... how you will know how many contacts is too many...when the alarm goes ... increase the resistance until you get a trigger event. ... you won't cause any false triggers. ...
    (sci.electronics.basics)