PIR sensitivity increase with age?

Jon5ja

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I told passgas55 I'd take a look at one of his MS20s that he was having trouble with sitting there retriggering itself several times once it'd been triggered. Sure enough, I went through, cleaned up the board, replaced just about every component except the PIR element, and the problem still existed. Finally, I replaced the PIR element itself out of one of my MS20s (both were the KDS elements and they looked just alike) -- voila! It worked.

In doing all this, I noticed that this MS20 with the original PIR element was MUCH more sensitive than any of my MS20s... I mean, I could just about stick a finger around the corner and activate the thing. Now, with the different PIR element, you actually have to walk in front of it or wave significantly to trigger it.

So... did I read in the archives at some point that as the PIR sensors age, they can become too sensitive (or noisy?) to use? I'd have sworn I ran across something here on JHP once that said something along those lines but I can't find it. Maybe I dreamed it.

I think my next step is to put PG55's original PIR element in my MS20, and play with the gain and see if it's a gain issue or if the element is just too noisy to be usable.

Jon
 



Archilochus

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Hi Jon,
Don't recall anything like that (but I forget almost everything after a week or so anyway.... :). Only thing I remember about aging is when Tinhorn recommended cleaning the optics occasionally to keep sensitivity from going DOWN. I'm guessing that any unusual behavior from the PIR elements is due to their relatively low quality.
Compared to the high-end Heimann elements, the KDS or Nippon Ceramic RE200B parts have pretty dismal specs (noise & part to part matching).
 

Jon5ja

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OK, maybe I did dream it :)

I can't really figure out any reason something like that SHOULD age, but it's strange that passgas55 has had at least 2 start misbehaving, and I think both of those were after he did the low-power mod. I actually undid all the mods one at a time after going over the obvious. I was certain there was going to be flux on the board causing leakage, or a noisy resistor, or a bad op-amp, or a bad voltage reference, or... but it turned out to be the element itself.

Oh well... I would like to hear from anyone who's seen anything similar.

Jon
 

Archilochus

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Interesting... would not have thought this... but was just paging through some Heimann PIR data books and came across a section where they recommend "standard" static precautions and handling.
Maybe the elements got zapped a bit during the low-power mods??

I've never treated the PIR elements as if they were static sensitive - no problems (yet).
 

Brian

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Hey Guys,

I never had this trouble with my PIR's or at least not yet. I use both the Heimann and the RE200B with pretty similar results. I wonder too if its the static discharge causing it.

I have one I built about 5 years ago with the same PIR going strong. I don't think the PIR ages but I guess it could be zapped accidentally. The only aging might be in the design with the caps or resistors.
 


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