Ethernet protection design for monitoring system

langtuodianzi

Ethernet protection design for monitoring system [Copy link]

Ethernet protection

Protection of Ethernet circuits requires a more delicate treatment, as the implementation (indoor vs. outdoor) will determine the level of robustness required of the protection device. The basic question that needs to be answered is whether the user is the only threat (consider ESD), or the port will also be subject to lightning transients. For installations where the Ethernet port is connected to a local router or indoor camera, there will be little chance of lightning coupling into the circuit, so ESD will be the only threat. In this case, the capacitance value of the protection device should be around 4pF or less, as the data rate is greater than 100Mb/s.

For those installations (equipment boxes) with long cables (100m) where Ethernet hardware is mixed with electrical hardware and circuits, standards such as GR-1089 can be applied. In these cases, the in-building code is the most important, which includes provisions for surges of up to 100A peak pulse current (for 2/10μs waveform) for 2-pair interfaces such as 100Base-T and 36.4A peak pulse current (1.2/50μs and 8/20μs waveform) per wire for 4-pair systems such as 1000Base-T.

For Ethernet installations where cameras are outdoors, the potential for directly coupled lightning transients is very high. One standard that covers this is the GR1089 inter-building specification. In this case, a lightning surge is defined as having a peak pulse current of 500A (for a 2/10μs waveform). Due to the extremely high energy, a thyristor-based solution is required for line-side protection. For the physical layer side of the transformer, installing a diode array can "mop up" any energy that is allowed to pass through the line-side protection.

Power over Ethernet

As mentioned earlier, the key to the ease of installation of many surveillance camera systems is Power over Ethernet (PoE). As expected, this adds another consideration to the protection scheme—one that does not exist in standard data-only Ethernet circuits. That is, at both ends of the application, the Ethernet line will be connected to a power source. On one side is the power supply equipment (PSE) that provides the power, and on the other side is the powered device (PD) that uses the power, such as an IP camera.

In addition to protecting the data lines, the power supply (PSE or PD) must also be protected. In other words, the data lines are protected based on the type of installation (ESD only or surge + ESD), while the power supply protection is added based on its unique needs. In addition, how the power supply is implemented (mode A or mode B) must also be considered.

Mode A and Mode B implementations refer to how power is added to or removed from the Ethernet circuit. For 100Base-T Ethernet, only two of the available pairs are used. The other two pairs are spare and unused. For Mode APoE, power will be implemented on the spare pairs. In Mode B installations, power will be implemented on the data pairs. Finally, it should be noted that the direction of the DC power signal (up to 57Vdc) is unspecified. It can be inserted into either pole.

The most common power supply protection scheme is to use a bidirectional TVS diode across the input and supply. The bidirectional diode is selected to bypass the line voltage regardless of polarity.

To ensure that security system components and network functions are reliable throughout the life of the installation, transient protection (ESD and surge) should be taken into account. In most cases, only basic ESD protection is required, while equipment or cables exposed to open outdoor environments should also be protected from the threat of lightning surges. Power circuits are also affected by transient voltage events and need protection. For all of these situations, there are a large number of solutions that will give circuit board designers more flexibility in their designs.

Jacktang

Are your protective gears okay?

Common

firefighterlee

This design doesn't seem detailed enough.

花鼓舞

This design doesn't seem detailed enough.