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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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You just explained why I can sneak past the detectors when the shop temp is
very high...and it gets VERY hot in here with everything closed-up, even with 10 hp of vent fans going. I had to go in today and show some stuff to a potential customer and I wish I had a video of me "sweeping" the plant with my 9mm Springfield...scared the crap out of the cat. No, I didn't have to smell Hoppies #9 when I got home. I'll try an IR source and a fan ainside nd put up some motion detector lights up outside with some type of noise maker that lets the thieves know they have been "seen" before they break in. "Gunner" wrote in message ... On Fri, 15 Jul 2005 22:27:14 -0700, "PrecisionMachinisT" wrote: Pretty sure that's correct.... As I understand it, these sensors pick up "average ir emmision".....this is sampled upon some established periodic ( time period )....if /when there is some change in total amount ir being recieved that is above (or below ) the 'setpoint' ( perhaps established as an average of the last ten samples or so)...(and it occurs within too fast of a time frame) then the alarm is triggered. -- SVL Sigh...most PIR detectors have a parabolic mirror element with multiple segments in multiple aiming paths. An infrared detector located at the focal point monitors the sum of the incoming infrared. (or a segmented lens with the detector element facing forwards) This makes the detector to have detection "fingers"....multple narrow "alleys" that the detector looks down. A moving heat source when passing through one of these "alleys", will spike the incoming infrared..and the detector will trip. Hold your hand over your desk, with your fingers spread. Your fingers are the sensitive zones. Now holding a lit match...pass the burning match under your fingers. Notice the pain occurs only when the match passes under the sensitive zone ? G PIR detectors have multiple zones stacked in multiple angles below horizontal so they may be mounted above normal furniture etc. Hold your hand out again, fingers spread. Now hold your other hand below it..fingers spread, and pointing downwards at a 45' angle. We have just added another layer of detection zones. Call in the wife, have her add her hands, both with spread fingers and pointing even farther down. Notice the area is still covered by alleys..but they start making a rather complex fence. But remember..few PIRS look straight down..so most have a dead zone below them..and hugging the wall may defeat detection, directly below the unit. Something to also consider as you ice your fingers from the match test..if you had moved the burning match towards and away from your hand BETWEEN the fingers...you have dead zones where nothing is detected until you get close to your hand. So when orienting a PIR device..it should be setup so an intruder has to cross the fingers, rather than moving towards or away the unit. There are many units with lens arraignments specifically designed to look in only one or several directions and angles. If you have pets for example..a unit mounted in a hallway..with NO downward looking zones prevents the mogs from tripping the unit. Some are designed to look in a 360' circle and are to be mounted in the ceiling in the center of the room, and so forth. There are some issues with PIR, besides the dead spots between the detection alleys. The #1 is the Mouse/Elephant Effect. The unit as we know..is sensitive to sudden changes in detected IR sources. This means it will detect a mouse at xx inches, or an elephant at .xx miles. G Aiming a PIR unit at an area that has BIG moving heat sources in the distance..outside for example will cause accidental trips . The other issue with PIR is and this is less common with newer units with better detection circuitry..is environmental masking. If the unit is looking at a wall that is 98.6F..it means each finger is receiving a heat signature the same as a human body. No detection unit can operated without false trips if it is only sensitive to a single "temperature", so internal temperature compensation circuits will change the sensitivity of the unit as the rooms temperature..or the background temp changes and over a time period..constantly. Remember...our detection fingers are looking at walls and floors. As they change temperature constantly through out the day and night. Lets say its in a steel building..and the ambient is 80F. One wall is 120F because the sun is shining on it. Suddenly a cloud passes..and that wall is no longer being heated. If there were no time/temp compensation circuity..the walls sudden cooling would generate an alarm as the detector would suddenly see a change in its input. And another alarm would occur the moment the cloud passed and the sun heated the wall again. The 3rd issue is the lack of sensitivity as the ambient temperature climbs..overloading the detector. Now it takes an elephant at xx inches to trigger the unit. Oddly enough..something cold can now trigger the unit..as its Below ambient..and the detector sees a negative spike PIRs are NOT universal units you can stick up anyplace and expect them to A. Work Every time, and B. Not trip by accident. Some thought in placement must be used when installing them. Unfortunately..Ive seen far too many lazy installers stick em up whily nilly and then leave. The major alarm companies tend to be the worst offenders for this. Frankly..they want the bucks far more than they care about providing you with a decent detection system. And remember folks..a burglar alarm system has NO protection value. It will NOT protect you from intruders. It will only detect them. Period. End Program. Full Stop. Next time an alarm co. sales droid comes calling..ask for a written guarentee that their system will protect your goods. Chuckle...watch em panic. Only the Deterent of getting detected and caught keeps the bad guys away. And if they know that the cops are 45 minutes away..they can be in and out long before anyone shows up. Gun and pawn shops are examples of high security, often with multiple alarms by multiple companies. (eggs in one basket is frowned on in such) and yet a band of bad guys who steal a truck, ram the front of the business and make off with a ton of Stuff can get away, unless other provisions are made..ram proof store fronts, lots of steel and concrete..etc. Gunner "Considering the events of recent years, the world has a long way to go to regain its credibility and reputation with the US." unknown |
#2
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I talked to one of my engineer's son, a cop, about video and he said:
"Great Idea! Just show the video to the inner-city Cleveland cops of some black men breaking in to your ghetto plant's refrigerators for food and the cops will run right out and arrest a bunch of them in a city-wide dragnet." "Jerry Martes" wrote in message news:0I8Ce.8471$Tx1.5178@trnddc03... "Tom Gardner" wrote in message ... I'm still getting broken into almost every weekend again and the thieves only get the employee's food in the refrigerators and make a mess. I have the tools locked-up. We have an ADT system with door contacts and 4 motion detectors. ADT wants $400 for a motion detector so my idea is to install some or all of the 10 I bought for $14 ea. on a separate system that triggers a relay to turn on a fan in front of ADT's motion detector. However, a fan won't trigger the motion detector. I can't "cut-in" to ADT's system actively so I need to do it passively...any ideas? (I won't sit down here with a gun, I won't make a batch of Exlax brownies! I do have an armed guard service that is in here every couple of hours.) Tom If you are interested in seeing who is entering, theres an inexpensive computer software program called "GOTCHA" that will record pictures on your computer whenever the image changes. It was originally designed to identify whoever entered an area to access some guy's computer. Jerry |
#3
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![]() Tom Gardner wrote: You just explained why I can sneak past the detectors when the shop temp is very high...and it gets VERY hot in here with everything closed-up, even with 10 hp of vent fans going. I had to go in today and show some stuff to a potential customer and I wish I had a video of me "sweeping" the plant with my 9mm Springfield...scared the crap out of the cat. No, I didn't have to smell Hoppies #9 when I got home. I'll try an IR source and a fan ainside nd put up some motion detector lights up outside with some type of noise maker that lets the thieves know they have been "seen" before they break in. snip Instead of noise, how about a recording. "Here they come..., you aim for the head, I'll aim for the balls." -- Gary A. Gorgen | "From ideas to PRODUCTS" | Tunxis Design Inc. | Cupertino, Ca. 95014 |
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