Microwaves Vs Ultrasonics

[james.wilson]

I had a discussion the other day regarding the merits of mics and ultrasonics.

Ultrasonics are a bit before my time so ive never done anything but take a few out. I do remeber alarmcom having an ultrasonic / pir dualtec.

The discussion was to do with european regs regarding seq confirm. In the UK we currently allow overlap of dualtec. This isnt permitted on other countries due to them being the same tech. So you could overlap a mic and ultrasonic, but you couldnt overlap 2 x mic / pir dualtecs.

My point is this

at some point in the past it was deemed that ultrasonic was a good detection method for use in buildings. Was this misguided? Is the theory sound but the units at the time were a little lacking due to tecnical limits at the time etc?

Could we make an ultra sonic based dt now, or even a mic / ultrasonic / pir proper tri tech etc? Would this get over the issues we have with mics in certain rooms, or would even a new tech based ultrasonic detector be a really bad thing?

[breff]

I would use a ultrasonic/pir over a dualtech in a conservatory if only I could still get them

[james.wilson]

yeah good point, well sealed etc. I assume they suffer from the some (nowhere near as many) of the same problems pressure wave detectors do, ie draughts, not particually well sealed buildings etc.

[arfur mo]

boy are YOU in my play ground now James lol!

imho Aritec made the best ultrasonics of the day called Advisor 1 and Advisor 3's, followed by Munford & White.

you don't get the same penetration through walls, but you do get area 'bleed' through holes.also say you have a unit in the lounge and one on the landing, with doors left open, they will act as expanders to each other, unless on different frequencies.

Aritec used this in a master and slave fashiom, have one receiver and up to 3 transmitters as slaves to cover the area or to dal with 'L' shape roms

Problems were with other sources of U/Sonics, like the old telephone bells and/or extension bells, door bels, time clocks. to cure it you had to put cellotape on the ringers to prevent the spurious frequencies from flooding the mic. escaping air from compressors was another one thigs like wind chimes were a no no.

they were also susceptable to moving air currents from fire places or air pricks, so no good in a draughty garage, would score well ina conservatory as long as all wndows are shut tight against draugts.

the transducers could also go off tune, i could ften hear this at the time as an intermittent warble, the frequency was knocked silly by the fault, i could also 'hear' ultrasonics but as a pressure not a tone, beleive it was really a harmonic but very painful, proved this ability several times by being in a room and telling other engineers when they were transmiting, they were switching them on and off randomly, but bet i can't do that now though.

when on a call out, i liturally stood still and listenned for these sources to crop up, obviously they were very quiet so you sort of ramped up your attention, i'd also check what time it went off, and see what time the clocking in/out was set for, as these tended to ring on Sat, Sunday and public holidays while alrm was still set, so to see if it coincided, even now i find myself still listening for dammed ultra sonic alarm causes if i'm in a quiet room, sort of self inflcted tinitus .

Arfur

[james.wilson]

lol i thought it might be your era.

re the cross talk and master slave thing. That would be no good under modern confirm regs, but id assume it could be sorted.

It appears no one makes a generally available ultrasonic anymore? is this a tech that has a place now, ie an ultrasonic/pir dualtec overlapped with a microwave/pir?

[hpotter]

as breff, modern us/pir be ideal in conservatory (esp if eg french doors to lounge shut), but doubt elsewhere & with conditions...

pretty much as arf said, re interference from bells, keys or postman. also remember customer dog gettin the ebee gebees - they ran @ around 40KHz, supposed to be just above dog hearing, but well within eg bats.

1st ones i fitted we used to solder together for firm was working for, design was firm owners. horsesar*e springs to mind.

assume could be made digital but then if cando, why not do same for higher frequencies (mw?), instead of just relying on doppler effect. then again we're getting into stealth tech.

[james.wilson]

There has been a serious lack of succesfull inovation in detectors for some time now.

[arfur mo]

Simular idea ti master nad skave US, given power of modern LEDs, even the one in the airwick stink arrester lights up the bungalow, often though IR sender middle of ceiling, and several IR receivers.

think tv remote, mine bounces signal everywhere, don't need line of sight, can even be ass on to the telly

Arfur

[arfur mo]

what ever happened to those low pressure wave sensors? some siezmics have a version of it to cut out trafic caused false alarms

they made a massive impact, salesmen infamously demonstrating by placing unit in a fridge and banging a window (totally ballsed up the secret lemonade drinkers amonst us), then seemed they died away nearly as quickly.

i used a couple, made in France iirc, shiny black bx no tamper . served a purpose where they had several dogs in the house initially allowed to roam unrestricted, and they worked fine,

still got one on a house thats been through about 5 diffeent owners over some 15 years, had conventional detection fitted/moved as you do, but they all like the unit as low level detection for when sleeping or for when guests stay over, its then on just with front door.

Arfur

[hpotter]

There has been a serious lack of succesfull inovation in detectors for some time now.

wanna say why reinvent the wheel, unfortunately, bs/en b*ggers keep changing the vehicle.