Hi, I wonder if someone can point me in the right direction. I have just had an alarm fitted to my Motorhome. Unfortunately the PIR gives false alarms, this could mean since I have a tracker connected to it I could rush to a site or home for nothing!

The PIR is at ceiling level and pointing to the back of the van, where it must see windows etc. When the sun comes roound it will trigger. I believe it is due to heat build up, although I have been told this is not possible.

The PIR seems to be a simple one but has an adjustable sensitivity control, I have turned this to minimum and it still gives false alarms. I have checked immediately the alrm has triggered and there can be no direct or indirect light falling on the sensor.

Please can someone tell me what type of sensor I need to get, it needs to be small, no taller than 100mm (4") preferably 90mm.

I live near LHR so any info on suppliers would be helpful as well.

Sorry for asking such a simple question, but I am sure somebody has met and solved this question.

Hi John,

rise in temperatures can indeed trigger normal PIR's.

this problem can be resolved by fitting a dual technology sensor such as a combined pir/microwave (the most common type)

do buy a Quality Branded detector though, a cheap £12 detector is asking for trouble.

Napco are a good brand (but expensive) as are Optex.

Texecom are also worth a look if your buget concious, good quality kit at a reasonable price.

Hope this Helps

Regards

Bellman.

I've installed d/t's several times in overly hot enviroments like this with no problems.

i do extensively adjust and walktest them though.

I aggree that Ultrasonic will also work but they are also not false alarm free.

As for Pete's Idea about Car Alarm Sensors, they are probably ideal since they are designed for the same enviroment..

Regards

Bellman

Many thanks for your replies.

I have veered away from ultrasonics because there is nearly always air circulating from rooflights etc. Unfortunately due to ventilation requirements all roof lights have to allow air in and there are a number of places at floor level as well. The air movement is not much, but I feel with my experince in cars they may be a bit 'dodgy'

The body behind the cab is fibreglass and this combined with polyplastic windows made me wonder about the dual tech, but presumably the mw part is adjustable, so if it was turned down would that be OK.

How much better are the Dual Tech than quad? If I had a quad and set the pulse rate if possible to say 3 would this be satisfactory?

The microwave element of a dualtec is ajustable in most if not all detectors i've seen but I'm sure their minimum range is still some 8 metres although this will be less if the detectors mounting height is reduced. I would have thought still too long for your motorhome. The microwave element also has a wide spread that would reach and break through the walls of the motorhome within a couple of meters. To have a dualtec fitted would mean a hell of a lot of adjusting including screening the sides of the lenses. By the time you are finished, it would be close to useless. A fibreglass body would not stop the microwave element detecting outside the physical perimiter of your motorhome.

Quads could be viable but you'd be defeating the object of installing one adjusting the pulse count to 3. Crow do a great quad, the SRP700 which if requested, can be fitted with a black lens which helps in those direct sunlight situations. The Crow Genius is another quad that is great in harsh environments. I've fitted one in one of those BandQ steel kit sheds with no problems. If no expense spared, the Crow D&D works fine in swimming pool areas and outside and works from 9vdc too.

Just out of interest. How is your alarm powered?

Tony

C+K DT 700, now the honeywell MX500 uses K band microwave, which I was led to believe does not penetrate building products (inc glass), although this could have been salesman's B.S.

In answer to:

Just out of interest. How is your alarm powered?

It is connected into a car alarm circuit which has a shock sensor.

There are three connections, +ve, -ve and to a -ve trigger. It is a twelve volt connection to the PIR, comes straight off the fuse box.

Really grateful for all your help, would I be right in thinking that a quad system without touching any pulse rates would seem to be the best solution. I suspect the one fitted is a cheap one and has no temperature compensation anyway.

(I knew virtually nothing about PIRs ten days ago, its surprising how much there is to know)

I used to fit car alarms and a microwave fitted centrally usually does a good job once youve set the 'bubble' correctly.

Thank you for your advice. In the end I fitted Scantronic 460 Domestic Twintec with it appears total success - No false alarms!

It is a compact sensor and ideal for the job.

Once again many thanks and thank you for sharing your exertise with me.

John

I reccomend the optex rx40 if you decide to use  a quad

Pete

That's a bit of a contradiction.

The RX40 is just a cheap Chinese dual element PIR. When they write "quad zone logic" that is just misleading marketing, although they have fooled a lot of people with it (including Gardiners who had it in the Quad section of their catalogue for a while).

Paper PCB, non screened relay, don't get me started....