I mention burglar alarm, but my question is applicable to just about any alarm "zone wiring" that is to be supervised.
How is this traditionally done?
Assume a loop voltage of 5 volts DC, with an end-of-line (EOL) resistor at the far end of the wire pair to be supervised. That arrangement will result in (3) circuit possibilities.
1) Current through resistor only (i.e., a known, pre-determined current value). This would represent the normal, no-alarm condition. I think? Pretty sure..
2) A SHORT across the EOL resistor, resulting in maximum current. This would be the alarm condition. And...
3) An OPEN in the zone loop wires before the EOL resistor, resulting in zero current (and hence, would indicate a "trouble" on the wiring.
My question is: Do alarm system designs use a bunch of window comparators for this? Or maybe an ADC? Or high-side current sensors across resistors on the panel side, or what??
I know these circuits have been around for DECADES, but as usual, I can't put my hands on one.
t the far end of the wire pair to be supervised. That arrangement will res ult in (3) circuit possibilities.
value). This would represent the normal, no-alarm condition. I think? Pr etty sure..
zero current (and hence, would indicate a "trouble" on the wiring.
nel side, or what??
put my hands on one.
I used to install burglar alarms. The basic concept dates back to when the y only had relays to do the logic. The railroad uses the same ideas to det ect the presence of a train while also monitoring for a broken rail.
The loop is a wire pair. It runs from the panel around the perimeter of th e building since that is where the windows and doors are that need protecti ng. One end of the loop is connected across a battery with a current limit ing resistor and the other end of the loop is connected to a relay also in the panel. As long as the relay has current, there is no alarm. If either wire in the loop is opened or a short is made across the pair, the current to the relay is interrupted and the alarm sounds.
Devices like window switches can be made to short the pair or two open one wire. Other devices can be used to do the same thing such as motion detect ors.
That's the old way... Now it is not uncommon for windows and doors to use wireless detectors that use RF links and ID codes to identify which door o r window is keeping you from arming the alarm. Or a combination could be u sed.
--
Rick C.
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t the far end of the wire pair to be supervised. That arrangement will res ult in (3) circuit possibilities.
value). This would represent the normal, no-alarm condition. I think? Pr etty sure..
zero current (and hence, would indicate a "trouble" on the wiring.
nel side, or what??
put my hands on one.
Anything and everything is possible to find in use. Some systems add some AC signal and then use some pre-defined capacitors/resistors to create a lo w pass filter for each zone. Using this method, it's more difficult to def eat or sabotage the alarm system, by any sort of wire cuts, shorts, or jump ers around any sensors. You can get this method working to where even the a dded human body capacitance of someone touching a bare wire (or using a met al tool) will upset the ac signal enough to alert that some "tampering" is going on.
t the far end of the wire pair to be supervised. That arrangement will res ult in (3) circuit possibilities.
value). This would represent the normal, no-alarm condition. I think? Pr etty sure..
zero current (and hence, would indicate a "trouble" on the wiring.
nel side, or what??
put my hands on one.
Old commercial fire alarms used 10A through the loop to find bad connection s. The terminators were back in the control panel. Standard Electric Time w as one OEM of these 100+ year old designs that are still in use in some pla ces. The high current loop helps locate loose connections, or when only one or two strands of the wire is caught under a screw. At least they got rid of those hand wound code wheels that interrupted a loop of buildings, back to the fire station. Each building was assigned a code of long and short pu lses. A chart at the FD told them the actual address.
Panel OEMs for modern systems don't publish any data about the control boar ds, for liability reasons. If they were online, it would make it easier for a professional to find the weak spots.
at the far end of the wire pair to be supervised. That arrangement will r esult in (3) circuit possibilities.
t value). This would represent the normal, no-alarm condition. I think? Pretty sure..
n zero current (and hence, would indicate a "trouble" on the wiring.
panel side, or what??
't put my hands on one.
ons. The terminators were back in the control panel. Standard Electric Time was one OEM of these 100+ year old designs that are still in use in some p laces. The high current loop helps locate loose connections, or when only o ne or two strands of the wire is caught under a screw. At least they got ri d of those hand wound code wheels that interrupted a loop of buildings, bac k to the fire station. Each building was assigned a code of long and short pulses. A chart at the FD told them the actual address.
ards, for liability reasons. If they were online, it would make it easier f or a professional to find the weak spots.
Lol, security through obscurity is a myth. It wouldn't be hard to gain acc ess to a control panel in an installation. Besides, for the most part ther e isn't much new under the sun. It's like safe cracking. Come out with a new lock and the bad guys have the info in a few months.
--
Rick C.
+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209
or at the far end of the wire pair to be supervised. That arrangement will result in (3) circuit possibilities.
ent value). This would represent the normal, no-alarm condition. I think? Pretty sure..
in zero current (and hence, would indicate a "trouble" on the wiring.
e panel side, or what??
an't put my hands on one.
tions. The terminators were back in the control panel. Standard Electric Ti me was one OEM of these 100+ year old designs that are still in use in some places. The high current loop helps locate loose connections, or when only one or two strands of the wire is caught under a screw. At least they got rid of those hand wound code wheels that interrupted a loop of buildings, b ack to the fire station. Each building was assigned a code of long and shor t pulses. A chart at the FD told them the actual address.
boards, for liability reasons. If they were online, it would make it easier for a professional to find the weak spots.
ccess to a control panel in an installation. Besides, for the most part th ere isn't much new under the sun. It's like safe cracking. Come out with a new lock and the bad guys have the info in a few months.
I did a bunch of building automation systems, for high-rises in NYC. I found it most efficient to scan/mux the loop currents into an ADC, to minimize the electronics per channel. I used an uncalibrated single-slope ADC, plenty good enough. The people who buy fire and supervision systems mainly want cheap.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
at the far end of the wire pair to be supervised. That arrangement will r esult in (3) circuit possibilities.
t value). This would represent the normal, no-alarm condition. I think? Pretty sure..
n zero current (and hence, would indicate a "trouble" on the wiring.
panel side, or what??
't put my hands on one.
ons. The terminators were back in the control panel. Standard Electric Time was one OEM of these 100+ year old designs that are still in use in some p laces. The high current loop helps locate loose connections, or when only o ne or two strands of the wire is caught under a screw. At least they got ri d of those hand wound code wheels that interrupted a loop of buildings, bac k to the fire station. Each building was assigned a code of long and short pulses. A chart at the FD told them the actual address.
ards, for liability reasons. If they were online, it would make it easier f or a professional to find the weak spots.
Typical of your nonsense. The information is not shared because of liabilit y. It also prevents 'Charley's Bait Shop & alarms' from doing half ass repa irs on the panels. I designed a nice panel with eight zones in the mid '70s . The least liability insurance we could by was $5,000,000, an it could go past $500,000,000 if it sold well.
There were fly by night alarm companies with no insurance. They bought flim sy wiring cabinets meant to consolidate the wiring in an area, and used use d relays. They charged enough that they could have sold commercially made h ardware and still made money.
Back then the market was dominated by brands like Ademco, FBI and Moose. Ad emco's first alarm bells were made from used brake drums. They still sold a lot of early relay designed systems in the '70s. Does anyone remember the fragile lead foil that was glued to large windows as a break detector?
'Fire Burglary Inc' made complete, all electronic panels.
Moose sold add on boards to upgrade old systems. Their first product was an electronic siren that sounded like someone had hit a moose in the nuts wit h a 2*4.
They could have lost everything, if they were sued. Alarms are a highly reg ulated industry.
at the far end of the wire pair to be supervised. That arrangement will r esult in (3) circuit possibilities.
t value). This would represent the normal, no-alarm condition. I think? Pretty sure..
n zero current (and hence, would indicate a "trouble" on the wiring.
panel side, or what??
't put my hands on one.
At one time, Trenton, Ohio considered any alarm that did not result in a co nviction as a false alarm. Twice in one year, required you to remove the sy stem. The Police were pissed off that any citizen felt the need for a alarm . On the other hand, if you paid the one approved alarm company, and for a leased phone line, they didn't care. That company was owned by some of the officers.
conviction as a false alarm. Twice in one year, required you to remove the system. The Police were pissed off that any citizen felt the need for a ala rm. On the other hand, if you paid the one approved alarm company, and for a leased phone line, they didn't care. That company was owned by some of th e officers.
Thanks guys! I'm going to recommend we go with an ADC approach. I just feel better about that mainly because I can do some "signal" conditi oning in software so as to avoid false alarms - and if we screw something u p, maybe I can "un-screw" it in software. :) Plus, I have all the code w ritten from another project (the 8/4 Microchip ADC on I2C interface). I fo rget the part #. MCS3208 or something like that?
Interesting point about the Trenton, Ohio police. It seems a bit onerous. What if it was an actual burglary, but they (the p olice) just couldn't identify and catch the thief? This arrangement seems like a disincentive for the police to do their job. Which I guess was the intent.
a conviction as a false alarm. Twice in one year, required you to remove th e system. The Police were pissed off that any citizen felt the need for a a larm. On the other hand, if you paid the one approved alarm company, and fo r a leased phone line, they didn't care. That company was owned by some of the officers.
tioning in software so as to avoid false alarms - and if we screw something up, maybe I can "un-screw" it in software. :) Plus, I have all the code written from another project (the 8/4 Microchip ADC on I2C interface). I forget the part #. MCS3208 or something like that?
police) just couldn't identify and catch the thief? This arrangement seem s like a disincentive for the police to do their job. Which I guess was th e intent.
I bet if you look at the actual policy, it's not what's claimed. There are cities and towns that start to charge for false alarms after a certain number. But I never heard of anything so ridiculous as considering an alarm that does not result in a conviction as a false alarm. They show up, the door has been kicked in, stuff is gone and they will treat it as counting as a false alarm? That implies they will not even investigate it .
a conviction as a false alarm. Twice in one year, required you to remove th e system. The Police were pissed off that any citizen felt the need for a a larm. On the other hand, if you paid the one approved alarm company, and fo r a leased phone line, they didn't care. That company was owned by some of the officers.
tioning in software so as to avoid false alarms - and if we screw something up, maybe I can "un-screw" it in software. :) Plus, I have all the code written from another project (the 8/4 Microchip ADC on I2C interface). I forget the part #. MCS3208 or something like that?
police) just couldn't identify and catch the thief? This arrangement seem s like a disincentive for the police to do their job. Which I guess was th e intent.
One man's home had been burglarized several times. He had an alarm installe d. The police caught the thief the next time, but it was thrown out of cour t on a technicality. The police decided that without a conviction, it was a false alarm and demanded that he remove the system from his home. This was prior to the availability of digital dialers with multiple zones and large 24/7 monitoring services. We tried to set up a small one inn Trenton. We w ere one block from the Telco C.O., but the trunk lines through downtown ran up to 20 miles. There was so much echo and distortion on the lines that it was impossible.
Trenton's City Attorney had gone to the City of Middletown for a copy of th eir alarm ordinance. He used whiteout to cover Middletown and typed Trenton in a different font. Then he turned in photocopies to the city government. The original was full of typos and had references to locations in Middleto wn that he missed. The typical monitored alarm used a pair of six volt lant ern batteries for power. They had to be replaced every 60 days.
My connection with that mess started out teaching better wiring techniques to the installers. Most had installed phones for Ohio Bell. They had no ide a how to do proper loops for monitored circuits, or the importance of low i mpedance connections to reduce false alarms.
n a conviction as a false alarm. Twice in one year, required you to remove the system. The Police were pissed off that any citizen felt the need for a alarm. On the other hand, if you paid the one approved alarm company, and for a leased phone line, they didn't care. That company was owned by some o f the officers.
ditioning in software so as to avoid false alarms - and if we screw somethi ng up, maybe I can "un-screw" it in software. :) Plus, I have all the co de written from another project (the 8/4 Microchip ADC on I2C interface). I forget the part #. MCS3208 or something like that?
he police) just couldn't identify and catch the thief? This arrangement se ems like a disincentive for the police to do their job. Which I guess was the intent.
e
it.
I was there. That city's cops were all on ego trips. Our office was across the street from their police and fire station. I could get to the site of a n alarm much faster than they ever did. That included one employee causing intentional false alarms because the owner didn't hire his buddy. It was a specialty machine shop that resharpened burrs. They had a lot of expensive tools and supplies. I had rewired the system when only the owner was there. I put each switch on a different zone, so all he tripped was a silent alar m. I caught him in the act of prying against an old wood door to trip the m ag switch. His mother in law lived next door. She called the police and tri ed to have me arrested. It turned out that he was the one stealing so he wa s fired and charged with Grand Theft.
BTW, one of the officers stopped me one day when I tried to return my siste r's lawn mower after I repaired it. He told me that I was under arrest. I d emanded to know what I was being charged with. He told me that it was none of my damned business. I asked if 'Joe' was still the chief of Police, and that if he didn't answer my question I was going to Joe's house and find ou t. It turned out that there had been a string of daytime burglaries, and th e suspect was driving a white pickup truck. My truck was white, but it was a stepvan. His logic was that the thief stole another white truck. He was a lso known as 'Crash', for wrecking every patrol car they owned, in under a year. I serviced the department's two way radios, and I was well known in t hat town.
'Crash' had also left one of their GE PE66 High Band VHF radios on top of a cruiser prior to high speed chases. Each time, they hit the pavement. The radios had a diecast aluminum frame that splintered on impact with the road s.
To show how stupid they were, the Fire Department still had an obsolete 60K hz wideband Motorola Twin V radio in their fire truck. Their license had ex pired years ago. When I pointed it out they said, "So what? They can't arre st us, we're the government." That was when I cut all ties with them, and l eft town.
You can buy a VISTA 20 control board on ebay for about $50. There is about 5V when terminated with te correct EOL resistance, 10V open and near 0 shorted. It can be programmed for some choices of ms delay to respond.
at the far end of the wire pair to be supervised. That arrangement will re sult in (3) circuit possibilities.
value). This would represent the normal, no-alarm condition. I think? P retty sure..
zero current (and hence, would indicate a "trouble" on the wiring.
anel side, or what??
t put my hands on one.
Not sure when you did this, but NFPA and ANSI have moved in with standardiz ation and certification, which probably means local law enforcement won't l et you register it without it. And then regardless, three false alarms and you're out, unless you pay big fines. And most of it is wireless cell phone based now. If you can use 2-sided tap e, you can install an alarm system.
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