Wiring and principle of wired detector
Source: https://vedard.com/blog/wiring-and-principle-of-wired-detector
Date: 2022/06/23
Refer to https://vedard.com/blog/wiring-and-principle-of-wired-detector/ with details
Why do we learn wiring and principle of wired detector？
Wireless alarm detector and IP monitor are easy to install. Home users can easily install and monitor home security themselves. In commercial security, the development of various wireless protocols such as NB-LOT and ZigBee has led to the development of more remote and reliable wireless alarm security products. Wireless alarm detectors are widely used in security and smart home systems.
But wireless alarm detectors have disadvantages. They are more expensive and less stable and safe. Wired detectors are still often used in industrial and commercial security projects.
In addition, wired detectors are used for early installed home security system, when replacing the detector, you need to buy the same type of wired detector to replace.
So, it is necessary to learn wiring and principle of wired detector.
There are a wide variety of wired detectors, including infrared detectors, infrared and microwave dual technology detectors, door and window switches, glass breaking detectors, water leakage detectors, vibration detectors, smoke detectors, gas detectors, infrared beam and microwave beam sensors. Different brands of wired detector can be replaced for each other.
Why are wired detectors more stable and secure?
The wired detector is not interfered by wireless signal, leading to failure of alarm sending. The power supply of the wired detector is provided by the alarm host, and the detector will not be idle because of low power or no power.
What happens if the wire detector line is cut or shorted?
There is special wiring of the last detector by adding EOL resistor at the end of the circuit to provide line supervision. With it, line cut or shorted will report fault to alarm host. We will introduce the wiring types and principle of wired detectors as following.
The wired detector alarm output loop has N/C (Short for Normal Closed) and N/O (Short for Normal Open). Usually, anti-theft detectors such as infrared intrusion detectors and door magnetic detectors use N/C circuits. When the N/C circuit is cut by thieves, the alarm will be immediately reported. Fire detectors and emergency alarm detectors such as smoke detectors and gas sensors adopt N/O circuit. When the N/O circuit is bitten off by a mouse, it does not send an alarm signal but a line fault signal. Therefore, monitoring personnel can correctly distinguish between alarm and line problems and deal with them in time.
The EOL resistor values are 1KΩ, 2.2KΩ, 4.7KΩ, 5.6KΩ and 6.8KΩ. This is determined by the alarm host. The wired detector alarm output N/C loop needs to add the EOL resistor in parallel. The wired detector alarm output N/O loop needs to connect the EOL resistor in series.
In N/O circuit, the resistance value detected by the host is EOL resistance value. When the loop is closed, the loop resistance value is 0, and the alarm host receives the alarm signal. When the thief cuts the line, the loop resistance value is ∞, and the alarm host receives the line fault signal.
Similarly, in N/C circuit, the host monitors the resistance value of the line as EOL resistance value. When the loop is disconnected or the thief cuts off the line, the loop resistance value is ∞, and the alarm host receives the alarm signal. When the circuit is short-circuited, the circuit resistance value is 0, and the alarm host receives the circuit fault signal.
If there are multiple wired detectors connected to the same defense zone, the detectors should be connected in series when their alarm output loop is N/C, and then series the EOL resistor with the last one. When the alarm output loop of these detectors is N/O, the detectors should be shunt in parallel, with the last one shunt the EOL resistor.
Wired detectors usually also have two TAMP terminals, which are used to detect and feedback when the detector is disassembled. There are 2 ways of tamper-resistance wiring.
One way is to connect the detector tamper terminal to the alarm host tamper zone. In this way, the connection is reliable and simple. Through the alarm host, the tamper resistance is separately programmed to monitor the detector’s tampering. When the cover of the detector is opened, the line is cut off or the detector is out of power, no matter whether the alarm system is armed or not, the tamper-resistance corresponding to the alarm host will be triggered and send the tampering alarm. But, the alarm will not be triggered when the tamp circuit of the detector is short-circuited, and there are risks.
2.Double EOL resistor wiring type
Double EOL resistor wiring has the strongest anti-disassembly identification of equipment and does not need to set a separate anti-disassembly area in the alarm host. The alarm host determines what kind of alarm happens by the different resistance values output by the detector signal line in different states.
Take N/C circuit and EOL resistor 4.7KΩ as an example. When there is no alarm or equipment line damage, the signal line end resistance output by the detector is 9.4KΩ, and the alarm host determines that the closed detector in the defense area is normal and there is no alarm.
When the conventional ALARM is triggered, NC and C terminals (or marked ALARM terminals) are open, and the resistance of the signal line end output by the detector changes to 4.7KΩ. At this time, the ALARM host determines that the defense area is open and the detector is normal. In the defense state, the ALARM system issues the corresponding ALARM according to the corresponding setting. (Normal alarm)
When the detector cover is opened, the equipment is out of power or the line is cut, the signal line end resistance of the detector output is ∞ (i.e., open circuit), the alarm host will be immediately triggered to send out the device disassembly alarm.
If the circuit is short-circuited, the resistance of the signal line end output by the detector is 0Ω, and the alarm host will be triggered immediately to send the disassembly alarm.
Regardless of the state of alarm system armed and disarmed, the disassembly alarm will start immediately. So the double EOL resistor wiring is the safest and most reliable way to connect.
When multiple detectors are connected to the same alarm zone, only the last detector is connected according to the double EOL resistor. The TAMP and alarm of the other detectors are short-circuited.
To facilitate installation, some detectors allocate the EOL resistor on the PCB. Only need to select the connection mode through jump. The principle is the same.
Last but not least, when programming the alarm host, the defense zones attribute of these detectors should be programmed according to the wiring way. That is the tamper-resistance zone, the single EOL resistor zone or double EOL resistor zone. If the programmed zone attribute and wiring mode are not consistent, the alarm system will always consider that the equipment is in a damaged state and constantly alarm can not work normally.
Refer to video guidance of FC-7664 setting and programming as below.
https://www.youtube.com/watch?v=TBgLnMI37R0