Answer to Question #101312 in Electric Circuits for Michael Thickens

Question

HI i have a IR photobeam sensor(12vd) to trigger a alarm system if some one gains access to our rear yard across the path so if they walk through it triggers, my alarm sesnor operates on a NC system, its all set up but the alarm sensor that talks to the alarm (a standard magnetic door sensor type with wired contacts) . The alarm sensor needs the circuit to be open for longer than the photo sensor does when you brake the beam aprox time 0.5 secs, it needs approx 2 secs for the alarm sensor to register it as open, (as like when you open a door)

what would be needed to extend the trigger time from the photo sensor ? as it works well if you stand in the way of the beam but if you pass trough by walking the photo electric sensor triggers but the alarm sensor does not as its so quick.
A time delay is needed when circuit is open

Answer 1

Adding a simple inductance coil in the circuit of the photosensor can increase the time constant. When the signal comes, the coil would not allow it to reach the threshold value quickly as before.