Talk:Passive infrared sensor

Contradiction - black body radiation

All objects emit what is known as black body radiation. This energy is invisible to the human eye but can be detected by electronic devices designed for such a purpose. The term passive in this instance means that the PIR sensor does not emit energy of any type but merely passively accepts incoming infrared radiation.

see also:

http://en.wikipedia.org/wiki/Infrared_motion_detector

This is contradictory. Having said that ALL bodies emit radiation (correct if above absolute zero?) the third sentence says that PIR sensors do not!

I made an edit to remove the contradiction: "All objects emit what is known as black body radiation. It is usually infrared radiation that is invisible to the human eye but can be detected by electronic devices designed for such a purpose. The term passive in this instance means that the PIR device does not emit an infrared beam but merely passively accepts incoming infrared radiation."

Bionic sensor

Can the bionic infrared sensor developed by Dedy Wicaksono (TU Delft) be mentioned ? http://dedywicaksono.wordpress.com/2008/10/21/my-phd-research/ —Preceding unsigned comment added by 81.245.64.190 (talk) 11:11, 8 July 2009 (UTC)

Infra

The prefix infra does not mean below our ability to detect it visually but simply means below. Otherwise other words with this prefix, such as infrastructure and infrasonic, would not make sense. Infra-red simply means below red and refers to light that is lower in frequency than red light. —Preceding unsigned comment added by 203.35.135.136 (talk) 03:10, 15 September 2010 (UTC)

Misleading first paragraph

The sensor does not measure heat of objects entering the field, it captures a virtual map of the surroundings based on heat signatures and ANYTHING entering that field will disturb the field and activate the sensor. It doesn't matter what temperature the moving object is, it could be exactly the same temperature as everything in the field. I made an edit but just added two sentences to clarify. I work in IED defeat (Counter IED) for the military and am trying to get them straight on this as well. — Preceding unsigned comment added by Mcgyver2k (talk • contribs) 16:37, 29 September 2011 (UTC)

Where is the evidence that objects at the same temperature can be detected? What is the mechanism of that detection? If I overpaint a picture with exactly the same colours, how can you tell? I don't see how it's different with infra-red. As for the claim that a PIR "captures a virtual map of the surroundings based on heat signatures", this appears to be false. The sensors have only three connections and their operation seems quite simple: they conduct a current which increases with the total incident infra-red light. A lens is fitted to vary the sensitivity of the arrangement in different directions, so that movement of an object at a different temperature across the field of view results in a variation in the total received light, even when the object remains entirely in the field of view and the background is all at the same temperature. I came to the article to learn more than these obvious points, but I read stuff I just don't believe. Mike Shepherd (talk) 19:31, 21 February 2012 (UTC)

"Where is the evidence that objects at the same temperature can be detected?" You can demonstrate this for yourself. Simply take an object in a room with a motion detector sensor that is the same temperature as everything els in the room, attach it to a handle of some sort, stand out of view from the sensor and then wave it (the item) in front of the motion sensor. I did this in a controlled environment (sealed box). I took a plywood box, mounted a sensor in it, cut a hole in the top of the box at the opposite end of the sensor and mounted a small piece of plywood inside the hole. I attached a piece of fishing line to the plywood, turned on the sensor and then slowly released tension on the fishing line and guess what? Yep, the sensor activated. Thus proving my point. By the way, the sensors don't detect "light" they detect heat but they only "activate" on motion.Mcgyver2k (talk) 08:19, 18 April 2013 (UTC)

I'm sorry, User:Mcgyver2k, but as far as I know, that is flat-out wrong. PIRs detect heat energy. They deduce motion by detecting changes in temperature at a given point. This is both my own experience, and the information provided by every source I've checked. I have just cited no less than seven different sources supporting this. As such, I have removed statements to the contrary from the article. If you have a reliable source you can cite, so that other can verify the claim, please provide it. —DragonHawk (talk|hist) 19:19, 24 June 2012 (UTC)

DragonHawk, I'm sorry but it's not wrong. See my explanation above and btw, you "cite" some pretty sketchy sites (forums) to try and validate your point but most of them probably got their opinions from Wikipedia to begin with so..... As a matter of fact, your 4th link is the source for your 3rd link (or vice versa) as they are both linked to Adafruit industries and attempting to sell the same product. Your 5th link actually validates my initial statement (that you deleted) when it states "This arrangement cancels signals caused by vibration, temperature changes and sunlight." Your 6th link is another sales site that states Pyroelectric sensors measure temperature but this is incorrect as they detect change based on temperature, not measure the temperature itself. Your 7th "cite" is another sales pitch. I'm starting to see a trend here. Are you using Wikipedia to drum up business? LOL

The internet is a wonderful thing, I could do a quick search (worded the right way) and have a hundred "websites" to "cite" in order to "prove" my point but that would not make me correct. Would it? When you have some authoritative sources and something more than a "hunch" that most of the commercial sites you like to visit are more correct than real life then feel free to edit my stuff. I'm putting it back until such time and we can do this every day if you like.Mcgyver2k (talk) 08:19, 18 April 2013 (UTC)

Mcgyver2k - I have to side with DragonHawk. Is there any chance that you're testing with a combination microwave-PIR detector instead of just a pure PIR? Also, your test setup, while ambitious, doesn't control the environment well enough to support the conclusions that you're drawing. You really need active temperature control of both the background & target object in order to conclude that the PIR can differentiate between two objects with the same temperature. Otherwise, there are simply too many variables to support your claim. FWIW, I'm an engineer & I design lighting controls. 24.21.16.40 (talk) 19:57, 4 July 2013 (UTC)

Anonymous - You can side with whomever you like, it won't make you any more correct. If you'd care to conduct your own experiment to prove it to yourself then that would probably settle this. I actually spent the time and effort to do so and that's why I'm pretty confident in my statement(s). I don't just make claims or tell someone "prove it" when I can check it out myself. People will lie, fib, stretch the truth and pretty much do anything they can think of (besides work) to make themselves feel good or important. To each their own.Mcgyver2k (talk) 17:17, 3 August 2013 (UTC)

History?

Do anyone have any information about the history of PIRs, such as when they were invented and were first used in alarms? — Preceding unsigned comment added by 130.235.35.168 (talk) 09:43, 15 February 2012 (UTC)

Can a PIR detector detect moving objects at a fixed temperature? Article says so, but does not explain

The article says two things which seem confusing to me - I can't see how they can both be true.

1) "Strictly speaking, individual PIR sensors do not detect motion; rather, they detect abrupt changes in temperature at a given point using the Infrared radiation level"

2) "Moving objects of identical temperature, however, will trigger a detection because that is the sensor's job, to detect motion. It detects motion regardless of temperature.[4] This is also why you can take a piece of paper from a desk that is the same, exact, temperature as everything in the room, attach it to a stick (also the same exact temperature as the room) and wave it slowly in front of a sensor (at any range within the limit of the sensor) and it will activate the sensor."

If objects of the same temperature are moved, how is motion detected? Could it be due to different emmisivities of materials? If that is so, and that is my best guess, it should be stated. But I have no idea if that is so. Drkirkby (talk) 09:06, 3 June 2013 (UTC)

DrKirby - I also noticed this while doing some casual reading. Seems that McGyver2k is working really hard to keep this incorrect information on wikipedia, possibly for commercial gain. 24.21.16.40 (talk) 20:05, 4 July 2013 (UTC)

I also noticed this while reading the article and was intrigued. The article states "Moving objects of identical temperature will trigger a detection..." and cites and article on the digikey website. I've read the referenced article (which is quite detailed) however I can't see where it states that objects of identical temperature will be detected; and in fact appears to describe that the mechanism of detection is based on differences in temperature. For this reason I have added a failed verification tag to that reference. For me to be convinced I'd like to see either a citation that either a) describes the mechanism by which a PIR sensor would detect movement of objects of identical temperature; or b) a peer-reviewed scientific experiment demonstrating that this occurs. If the referenced article is long; then it would be good to quote the relevant section of the article here on the talk page for the benefit of myself and the others above that have clearly come looking for an explanation. 2001:8B0:1623:0:3993:B1A:2E98:236 (talk) 17:18, 26 July 2013 (UTC)

Here's the thing, first and foremost, I have nothing to gain financially from keeping this information on wiki, I simply want the truth and facts to be known. If you don't particularly 'like' my source that does not entitle you to call it "failed". The link goes to an article where it clearly says "objects of the same temperature will trigger a detection" that is all I was saying that the link said. It's pretty cut and dried. If you need more scientific evidence than this then you have a personal problem and you can either go dig for it, run a test yourself or simply get over it. There may not actually have been anyone that conducted a peer reviewed study on this exact scenario as of yet. Hey, you could be the first.

As for the contradiction between #1 and #2, I didn't write #1 and it isn't totally incorrect so I left it alone. I added #2 to clarify and illuminate.

I work in the electronic warfare industry creating ways to detect, intercept and jam all kinds of things for the military. That's all I'm allowed to say about that. — Preceding unsigned comment added by Mcgyver2k (talk • contribs) 17:04, 3 August 2013 (UTC) Mcgyver2k (talk) 17:11, 3 August 2013 (UTC)

I think you are missing one key insight. The sensor does not have a uniform field of view. Within the overall field of view there are sensitive areas separated by insensitive areas. An object moving across this field will cause the amount of light hitting the sensor to vary as it moves in and out of sensitive areas. Take a look at U.S. patent 3,703,718 issued Nov 25 1969 to H. L Berman. The detection circuit is insensitive to the absolute light level but responds to changes in intensity caused by the motion. AJim (talk) 05:29, 20 March 2015 (UTC)

I am trying to analyze and describe the operation of the motion sensor as a combination of filters.

• The first, and most discinctive, filter is a spatial filter. Quoting from the abstract of patent 3,703,718: "... a single sensing element and optical means for focussing infrared radiation from one or more discrete fields of view on the sensing element. ...". It is the motion of objects into and out of these fields that is detected.
• There is also an optical bandpass filter in front of the sensor to restrict the range of wavelengths it responds to, to block the effects of visible light for instance. The patent describes the preferred optical passband as "4.5 to 20 microns".
• Changing light levels at the detector, caused by objects moving in and out of the various fields of view, cause fluctuations in the detector output. There is a frequency bandpass filter after the detector that only passes relatively sudden fluctuations in detector output, specifically those associated with people walking through the fields of view. The patent describes the preferred range as "0.2 to 3 Hz". The lower frequency cutoff rejects output changes due to slow changes in ambient temperature and such, while the high frequency cutoff rejects many of the fluctuations caused by random noise, or the fluttering of leaves, for instance.
• There is a signal level filter following the bandpass filter, amplified fluctuations must exceed a specified threshold to trigger a respones. This is a kind of sensitivity control. AJim (talk) 19:20, 25 March 2015 (UTC)

If I might add my experience to this debate, I don't think anyone is actually wrong about it. However, in theory a PIR detector will only pick up movement based on an abrupt change in temperature (as normally calibrated). This means that movement of an object emitting the same level of IR as the background won't trigger it. However, it seems to me that in practice a lot of unlikely circumstances have to be met. For example, the temperature of the background has to be uniform, which it never is. Also, the object must be emitting the same amount of IR as the background - this isn't necessarily just because they're the same temperature - think about it - you can fool and IR thermometer with something reflective.

So whilst I'd agree in theory that the article may be wrong, in practice it's correct - being the same temperature as the background will often trigger the sensor too.

F J Leonhardt 13:16, 25 September 2016 (UTC) — Preceding unsigned comment added by Fjleonhardt (talk • contribs)

Different practical types such as Dual Technology, Quad and so on

I'm not the ideal person to write this but if someone closer to the PIR industry could that'd be great...

In practical terms, real-world PIR detectors of the type described have various tricks to avoid false alarms. For example, additional volumetric sensors can be added to confirm what the PIR sensor is seeing (called Dual-Tech sensors). I use "quad element" sensors, which have a higher immunity to false alarms (from manufacturer's claimed, and experience), and I guess they have four sensors in one housing but I don't really know.

There is also optional temperature compensation, claimed to improve accuracy. F J Leonhardt 13:06, 25 September 2016 (UTC) — Preceding unsigned comment added by Fjleonhardt (talk • contribs)

I might help hear out but I'm in a dilemma since I'm an applications engineer at a company producing those sensors. I can contribute a lot to that page but I would always need to link to our resources which might implicate advertisement. I certainly do not want to advertise on an open platform but it is difficult to find guidance to that. What do you think about using multimedia such as https://www.youtube.com/watch?v=X07kX89NM30 . Since I'm the producer, I could create spin-offs without product placement. PrometeuszJasinski (talk) 11:15, 4 May 2017 (UTC)

Practical Implementation

Said paragraph currently includes "and fed to a transistorized relay driver circuit." Really? Always?? I would think that in many cases nowadays, the switching would be electronic rather than electro-mechanical. 94.30.84.71 (talk) 10:19, 7 November 2019 (UTC)

Passive or pyroelectric

The lede says the "P" means passive. Some say it means pyroelectric. Is one more correct than the other? Should the pyroelectric hypothesis be mentioned as well? Oh, and there is no link to Pyroelectricity in the article! I am shocked! Shocked, I tell you! :-) 85.76.78.82 (talk) 14:51, 4 September 2020 (UTC)