What’s your best guess? In a big storage room I have a motion sensor instead of a light switch. Makes it convenient when hands are full. Also like it turning off automatically. Was working fine for the last year. Suddenly it stays on all the time. Actually, it switches off, but then kicks back on within a half second. What’s the likely cause? Bad switch? Bats flying around setting it off? And what could cause it to just start that out of the blue?
Had trouble with the original one installed there. Electrician put in two originally–one at each end of room–but when they acted flakey in a similar way we guessed one might be triggering the other, so we removed one. Worked fine for a year or so, but no longer.
Replies
Cloud:
For Pete's sake, it's barely a fortnight away and you're still wondering what is tripping your sensor? You even name the cause in your thread title. I'll give you a strong hit, and demonstrate my psychic poers: Are you the original occupant of your dwelling?
Regards,
Rework
Yes, Cloud is the orginal owner/builder. So that is not the problem.
But I he just *might* have built over an acient indian burial gorund!
Ah William, you swiped my second psychic vision...
Regards,
Reword
I have one on a barn that heavy rain can set off. Of course cats and mice set it off as well. It makes you wonder when you look over there in the middle of the night, what's going on, motion wise. h.
Those things are a pain. They go out every year or two. I gave up on them.
Excellence is its own reward!
We love em. For reasons I don't know, sparky used a different style in this room than in the other closets. (That's what I get for allowing subs the freedom to think......hey, hey, just kidding!!!) No problems with the one model, only this one. Just trying to see if there could be other causes before I spend the money and time to replace it. Only use them in closets, which makes them good with full hands, so you don't have to do that elbow thing to hit the switch.
I use jamb switches in closets. Pain to install but dependable..
Excellence is its own reward!
But that would involve actually completing the job of installing all the doors. I've only had two years since move-in. There's only so much one person can do. :)
Generally there are 2 varieties of Occupancy sensor. (in the fiscally responsible world)
One is infrared which has a plastic lens cover with facets either on the inside or outside of the sensor. These track movement based on thermal images moving from one zone (facet)into the next. As a thermal object moves the background image diminishes. In cold environments a naked body works real well to turn it on. In a 98.6 degree environment it doesn't work well.
The other is ultrasonic which has a mesh or grill covering the material. Sonar in the above hearing range is what these are. They send out a ping and look for a Doppler effect. As something moves, the sonic signature changes. This turns the electronic switch thus the light. A timer holds it on to eliminate short cycling. They would seem temperature independent but it isn't really so. In cold weather the air is denser, and sound travels faster. Thus, this senses further. In warm weather the air is less dense and sound travels slower. Thus you have to come closer to the sensor for it to activate.
What causes failure?
Operator malfeasance. Kids playing with the switch moving it on or off then changing the timing on the delay-off. (check the setup) or they puncture the septum of the sensor and ruin the sensor
Lightening & overloaded circuit. This is a solid state circuit. That means that electronically there is a "transistor" turning the load (light) on & off. If you put too much voltage (lightening strike) or current (too big a lamp load) thru it the switch is destroyed. (it can fail on or off that is why SS circuits are rarely used in safety circuits)
It is too warm for the infra red circuit to sense a difference between the body entering and the ambient area.
Most often it is the lightening that toasts the switch. Put a surge breaker in your load center and it will bleed the excess voltage of a lightening strike to ground. Lightening can be as much as 300,000 volts. When it hits a power line in your area you generally don't get that much in your house. Instead there will be a miniscule 5000 volt surge for a nanosecond or 2. Voltage and solid state circuits are kind of like being a little pregnant. There is a threshold on a solid state switch that when met renders the circuit toast. Your light bulbs and all of your electrical appliances will last longer if you put in the surge breaker. Square D sells them for the QO load center. Most other manufacturers should provide the same type of product. Match the Manufacturer of the load center to the surge breaker.
PS you can't fix it. buy a new one.
Valuable response!!!!!!!
So the Fred Flintstone Version has a bat or a pit viper sitting up there turning it on and off?.
Excellence is its own reward!
Edited 10/17/2002 6:39:20 AM ET by piffin
The one we didn't cover was the capacitance sensor. This is Spooky in that the high end customer uses this motion sensor to detect prowlers. This is a field coil that changes its electrical properties when mass enters the sensing zone. This falls into the Ollie North security system world. At better than a grand each, you won't find them in the linen closet as they sense thru the wall.
I suspect that in fred's world the Capacitance sensor would be the pit viper. My favorite was the garbage disposal mini-dinosaur.
A good generic descriptions, but I would like to make a couple of additions and clarifications.
"(it can fail on or off that is why SS circuits are rarely used in safety circuits)"
I worked on some rail road grade crossing control systems. They where electronic to sense the motions of the train and where designed to be fail safe.
But they held in a gravity overated relay and the contacts where carbon. Gravity so that it did not depend on a spring that could fail and the carbon contacts so that they could not weld.
"This is a solid state circuit. That means that electronically there is a "transistor" turning the load (light) on & off. If you put too much voltage (lightening strike) or current (too big a lamp load) thru it the switch is destroyed."
"There is a threshold on a solid state switch that when met renders the circuit toast."
Not exactly. Now I agree that most likey his device was damaged by a transient. But it is not broken on or off or it would be always on or off which is not the case here.
What can happen is that it can be "partially pregnant" <G>. Maybe the gate on the output device is damaged so that there is some leakage current, but not enough to actually trigger it. But anytime the line voltage is a bit high then it will trigger.
Or the one of the transistors in the amplifier that process the signal from the IR sensor is damaged so that the balanced amplifier is no longer balanced. But it is now a nice tempature sensor. So a some changes in temp will cause it to trigger.
"Your light bulbs and all of your electrical appliances will last longer if you put in the surge breaker. Square D sells them for the QO load center. Most other manufacturers should provide the same type of product. Match the Manufacturer of the load center to the surge breaker."
You can also get 3rd party ones that mount on the outside of pannel and are connected just like another branch circuit. Intermatic and others make them. I think that Sq D has one also.
" Lightening can be as much as 300,000 volts. When it hits a power line in your area you generally don't get that much in your house. Instead there will be a miniscule 5000 volt surge for a nanosecond or 2."
Actually if it did hit the power line in your area there is a good chance that it would be too much even with the whole house type of protector.
What is more likely is that the lightening hit the tree a block a way. And that does induce surges into the power line. Those are a weaker surge that the protectors can handle.
But more likely you can get the surges from other sources such a tree limb falling across two line knocking one into the other. Or a car knocking down a pole. Or the fried animal on the transformer syndrome.
Well put in all cases.
The safety circuit I am most familiar with is related to Press controls (punch presses). In those applications there is a redundant circuit with a timer to make certain each input and output behave properly. If one freezes, one way or the other, the watchdog circuit trips the control system.
Surge protection is a combination or preparedness & dumb luck. If your number is up nothing short of a $10,000 system and fuses will CYA. Proximity to the strike means everything like you stated.
Intermittent and fluky problems are best explained by your leakage current description. I'm impressed. Generally solid state issues are met with a glassy stare by my customers of industrial control.
The beauty of the surge breaker I described is that you don't need to have the two pole breaker feeding the out of panel variety. The surge breaker is an all in one device. One other point worth mentioning is you are supposed to put the surge breaker, or the two pole feeder in the case you described, in the closest position to the main breaker in the load center.
Thanks for the clarification. You are a wise man in your shorts.
Edited 10/17/2002 11:50:28 AM ET by Booch
"You are a wise man in your shorts."
Darn I am have to remember to turn off that cam before I log on here.
BTW, my backround is as an electrical engineer, but now days mostly do software for embedded microprocessors. They have been used for such things as controlling the depth of a plow to monitoring and controlling pumps on water distribution systems.
Does this make sense...
The power flickered this morning, enough to shut off the computer, but no longer than a half second.
Since then, that storage room light has worked just the way it should. Is there a logical explanation for why that would make a difference?
Cloud:
1). Correlation does not imply causality,
or
2). The ghost in the machine's heart (clock circuit) was defibrillated by the spike in the juice...
Regards,
Rework
I know it doesn't necessarily imply it, that's why I'm asking if this could be such a post hoc, propter hoc situation. Maybe there's something in the device that gets reset when power is cut, for example. I don't know.
Cloud--
Not an electrician, was taking a very dry stab at humor. Nevertheless, was wondering if the voltage spike could have reset the clock circuit in your sensor, was hoping a pro would be by to comment....
Regards,
Rework
Last thought as you were speaking of the water distribution systems, those are a great ground!
I have a customer that buys the Intermatic surge arrestors for the third world water supply systems he makes. The surge arrestor he gets is shaped like a plastic grenade and amazingly enough when the lightening strikes the system it goes off like one. If you use that type, make sure you use a handy box around it. Further, when the electricity is shunted to ground the wire that does the connection to ground should not be in plastic wiring duct. The heat of the electricity from the lightening strike will spontaneously smoke that stuff.
Wow. Cool. Thanks for taking the time to try to make me smarter!
Some require reseting if the power was shutoff, a lot of them will switch to manual if the power is not restored after a period longer than 10 seconds.
Doub't thats the case in this instance but it's worth a try. You did keep the instruction manual didn't you?