A fair bit of freq. same principe but different frequencies

im sorry i think the question i meant to ask is 'what are they?' are they the gadgetry inside the sensors in the corner? i thought they used infrared sensors to detect movement.

Edited November 27, 201213 yr by ijoey

Ultrasonic uses sound a bit like a bat hears, the sound bounces off walls and stuff in the room, if something moves the sound that comes back is different (They are not used so much nowadays, apart from with car alarms) Microwave uses Radar Doppler it will see through walls fllors and cielings again radar coming back is looking for changes

im sorry i think the question i meant to ask is 'what are they?' are they the gadgetry inside the sensors in the corner? i thought they used infrared sensors to detect movement.

Infra red is looking for moving heat they work much like the Police action cameras on the helicopter, the infra red sees a heat object as say white in a black background, the detcetor will ignore stationary heat objects such as radiators, but will activate on moving ones 

ultrasonic and microwave both work using doppler shift and are both an 'active' sensor. PIR or passive infra red is a 'passive' sensor detecting ir changes.

 

The detection and false detection characteristics are different for all 3. There are many other sensing techs but pir and mw are the most used

ultrasonic and microwave both work using doppler shift and are both an 'active' sensor. PIR or passive infra red is a 'passive' sensor detecting ir changes.

 

The detection and false detection characteristics are different for all 3. There are many other sensing techs but pir and mw are the most used

Mcrowave uses radar doppler Ultra Sonic uses doppler velocimetry

fantastic. i appreciate all the information. BS50131 mentions that infrared and either ultrasonic or microwave can be combined. so this is to reduce the false detection? is this all within the sensors in the corner? and how do you ensure you are sending the signals all around the room?

and how do you ensure you are sending the signals all around the room?

The component standand shows how to test this and if claiming compliant must meet that test req.

Yes its the detectors in the corner, you install the detector set it at its lowest setting and walk test it and turn it up bit by bit until you have acheived the limits of the room. TBF Dualtechnology detectors are usually only used as a second detector in high risk areas or in hostile areas such as warehouses or garages etc. We would install PIR in most domestic applications

ah, all this is beginning to make some sense.

is there a particular place where the bell/klaxon has to be placed?

 

so when suppliers get hold of the intruder alarms, they are required to have some sort of qualification to fit them? is that where DD243 comes in?

dd243 is an old draft and has been replaced by bs8243.

 

Its mainly a confirmation standard and nothing to do with qualifications

ah, all this is beginning to make some sense.

is there a particular place where the bell/klaxon has to be placed?

 

No particular place, but it should be out of reach

 

 

so when suppliers get hold of the intruder alarms, they are required to have some sort of qualification to fit them? is that where DD243 comes in?

Standards are what we install to, qualifications are a completely different story