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| Is this correct in English? |
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| Stray Electron:
--- Quote from: CatalinaWOW on August 02, 2023, 07:13:06 pm ---Other than the suggestions above, I can think of no term to describe the condition. But perhaps I am not understanding the concept. It seems the idea is to make the desired detection condition have the same result as a fault condition, hence some action is always taken if a fault occurs. But this is only meaningful if there is a dominant fault condition. In the stated example if the switch were to close when the protected door/window opens an open would prevent detecting the event. But if the switch opens when the window/door opens a short would prevent detecting the event. Thus having a normally closed switch is only "fail-safe" if opens are the dominant failure mode. Depending on the specific installation this may not be true. A short caused by a nail or screw being driven through the wiring may be more likely than opens due to thermal cycling or rodent damage. More robust fault detection methods are available, but I know of no single word english description that identifies a specific approach. --- End quote --- Generically those conditions are described as a "false negative" or a "false positive" and those terms are used in many industries, particularly in testing. Literally in all kinds of testing; including medical test, drug testing, electronics testing, etc, etc. You can find descriptions of both terms on Wikipedia and in many other places. That's not a one-word description but it's the closest thing that I know of. |
| coppercone2:
as far as I know it would be referred to as -open and short circuit detect capability but yeah germany is known for making mega words is it called Unterbrkurzsechungennachweisen |
| Haenk:
--- Quote from: CatalinaWOW on August 02, 2023, 07:13:06 pm ---A short caused by a nail or screw being driven through the wiring may be more likely than opens due to thermal cycling or rodent damage. --- End quote --- The intention is to detect a cut wire (in alarm systems). So essentially you create a tri-state wiring: open (door/window switch is open, when door/window is opened - or when the wire is cut), short (that would be an error state) and resistance (loop completed and intact). The "open" condition should raise an alarm (when armed), the "short" should create an error. We have this kind of installation in our office, and the yearly service includes disconnecting the devices (PIR sensors, contacts) and measuring the loop. |
| CatalinaWOW:
--- Quote from: Haenk on August 07, 2023, 01:12:54 pm --- --- Quote from: CatalinaWOW on August 02, 2023, 07:13:06 pm ---A short caused by a nail or screw being driven through the wiring may be more likely than opens due to thermal cycling or rodent damage. --- End quote --- The intention is to detect a cut wire (in alarm systems). So essentially you create a tri-state wiring: open (door/window switch is open, when door/window is opened - or when the wire is cut), short (that would be an error state) and resistance (loop completed and intact). The "open" condition should raise an alarm (when armed), the "short" should create an error. We have this kind of installation in our office, and the yearly service includes disconnecting the devices (PIR sensors, contacts) and measuring the loop. --- End quote --- With that in mind I don't think there is a single word description (or English compound word) that fully describes it. A current loop comes close, but there are applications of current loop that don't categorize fault states. Your paragraph is about as short as it gets. I would also comment that if this approach is so widely used in Germany that a single word description has proved useful it would also seem that those in the habit of defeating such systems would be well aware of the needed bypass resistance required to stay in limits (a value chosen to not break the low limit when installed and not trip the high limit when the wire is cut. If the limits are set tightly to prevent this approach it would increase manufacture and installation costs, increase false alarms and still be susceptible to a more sophisticated bypass that cut the wire and inserted resistance at the same time. Then you end up discussing how sensitive the glitch detection can be made while not triggering on every motor start, lightning strike and load switch in the area. |
| EPAIII:
Am I reading this wrong? You seem to say: 1. "open (door/window switch is open, when door/window is opened - or when the wire is cut)" 2. "short (that would be an error state)" 3. "and resistance (loop completed and intact). The "open" condition should raise an alarm (when armed), the "short" should create an error." I inserted the spaces and numbers for clarity. Conditions 1 would seem to be both alarm and error states. And condition 2 would also be an error state. I would think that two arrangements would be possible: First, with the door and window switches in series and using the NC (normally closed) contacts to indicate they are closed. And a termination resistor at the end of the line. 1. Loop shows resistance to indicate all wires are OK and doors and windows are closed. 2. Loop shows open to indicate alarm due to open door or window or cut wire. 3. Loop shows short to indicate short as an attempt to bypass the security. This would also be an alarm condition. Second, and perhaps a better arrangement with door and window switches in parallel and using the NO (normally open) contacts to indicate they are closed. And a termination resistor at the end of the line. 1. Loop shows resistance to indicate all wires are OK and doors and windows are closed. 2. Loop shows open to indicate a cut wire. 3. Loop shows a short to indicate an alarm due to an open door or window. The problem with the second arrangement is that the individual door or window switches can be disconnected without cutting the loop by bypassing the connections to and from the switch before cutting them from the switch. No system is perfect. --- Quote from: Haenk on August 07, 2023, 01:12:54 pm --- --- Quote from: CatalinaWOW on August 02, 2023, 07:13:06 pm ---A short caused by a nail or screw being driven through the wiring may be more likely than opens due to thermal cycling or rodent damage. --- End quote --- The intention is to detect a cut wire (in alarm systems). So essentially you create a tri-state wiring: open (door/window switch is open, when door/window is opened - or when the wire is cut), short (that would be an error state) and resistance (loop completed and intact). The "open" condition should raise an alarm (when armed), the "short" should create an error. We have this kind of installation in our office, and the yearly service includes disconnecting the devices (PIR sensors, contacts) and measuring the loop. --- End quote --- |
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