What is Power over Ethernet (PoE)?

What is Power over Ethernet (PoE)?

As our Professional CCTV Experience

Power over Ethernet (PoE) is a method whereby power is transmitted to Ethernet-connected equipment (VoIP telephones, WLAN transmitters, security cameras) from the central switch. By using the existing CAT-5 cabling, the need for AC power (and wiring costs) can be eliminated. The switch is also able to control power distribution to the powered devices allowing sophisticated uninterruptible power management for vital systems.

Operation

Fundamentally, a PoE load or Powered Device (PD) must fulfill three functions in order to act in conjunction with the sending end Power Sourcing Equipment (PSE). The functions are Detection, Classification, and Under-voltage Lockout.

Detection Phase

When a PoE-enabled Ethernet cable is plugged into a PD, the PSE interrogates the device to determine if it is PoE-enabled. This period is termed the detection phase. During the detection phase, the PSE applies a voltage ramp to the PD and looks for a characteristic impedance from the load (25 kO). If the correct impedance is not detected, the PSE assumes that the load is not PoE-enabled and shuts down the PoE sending end. The system then operates as a standard Ethernet connection. If the signature impedance is detected, the PSE moves on to the classification phase. The signature identification voltage is a ramp voltage between 2.5 V and 10 V. A 24.9 kO resistor provides the correct signature impedance for detection (see Figure 1).

Classification Phas
 
The PSE continues to ramp the voltage to the PD. Between 15 V and 20 V, the classification phase occurs. During this voltage transition, the PD must draw a specified current to identify the device class (see Figure 2). The simplest class (Class 0) is also implemented by the use of the 24.9 kOhm signature resistor. The classification current describes the amount of power the PD will require during normal operation. It is this information that is fed to the controller by the PSE, which allows the system to determine power budget requirements. A table of classification current and operating PD power requirements is shown in Table 1.

Turn on phase

After the classification phase, the PSE continues to ramp the input voltage up to 30 V, when the under-voltage lockout (UVLO) circuit is released and the PD is allowed to power up. Soft-start circuitry is required to limit the current drawn from the PSE. A typical under-voltage lockout circuit is shown in Figure 3.

 

By this process, the PSE and PD work together to determine the nature of the load and apply power only to PoE enabled equipment. The system controller at the central location can determine load requirements and allocate power according to an operational needs hierarchy during power failure from its available UPS budget

For additional information about driving PoE compatible load equipment and circuits for implementing Class 1 through Class 3 classification, see Design Ideas DI-70 and DI-88.

For more info please visit to www.guardtech.com.my or Call +6016-666 1221 / +6019-900 8288

The Viewing Angle of CCTV Camera Lens

The Viewing Angle of CCTV Camera Lens

Usually, at the market, we can see that the same CCTV camera we can make it at the lens of 3.6mmm, 4mm, 6mm and so on. So you may wonder what is the difference between them? How far it can “see” for the CCTV cameras? Here the “see” means we can see the objects clearly, like the car number clearly.

Here we will begin with the fixed CCTV camera lens. Obviously, the fixed lens means the focus and iris are fixed and can not to be changed.

For the 3.6mm CCTV lens, its viewing angle is 75°and can see the car number plate clearly at the distance of  2.5m.

For the 6mm lens, its viewing angle is 60° and can see the car number plate clearly at the distance of 5m.

                                              

For the 8mm lens, the viewing angle is 40° and the distance is 7m. 12mm, the 12mm lens, its viewing angle is 30° and the distance is 10m.

Of course, beasieds the fixed lens, we still have many many other kinds of lens on CCTV cameras., luje the varifocal lens, varifocal lens with auto Iris, and so on. We will talk about them at next time.

For more info please visit to www.guardtech.com.my or Call +6016-666 1221 / +6019-900 8288

CCTV Analog and IP Resolution

CCTV Resolution for Analog Cameras

Customers often ask what kind of resolution is best for their particular CCTV system. Picking the right resolution for your surveillance camera can make or break your system.

Understanding the differences between Analog and IP can go a long way in determining which equipment to purchase.

For standard analog cameras, resolution is measured by TV Lines.  For most new analog cameras the TVL range is 420 to 700.  Although 420 TVL is considered the lowest, I’ve seen camera systems where the user was only covering a short distance and the video quality was actually pretty good.  Don’t automatically assume a low res cam is garbage.  For short distances, the low resolution camera could save you some money and put a good image up.  Now, the 600 TVL and above have excellent images.  The pictures are sharper and the contrast is great.

If you want great clarity the 600+ range of resolution is the way to go.  There are other factors for a good clear picture like lenses, lux, wide dynamic range, etc.  Make sure you speak to a pro about your needs – 016 666 1221 or 019 900 8288

CCTV Resolution for DVRS (recording resolution)

Once the camera captures the images that you want, it will send them through coax cable (or Cat 5 with Baluns) to the DVR.  At the DVR, the images are converted from an analog signal into a digital format to be stored on a hard drive.  This is the most important part of the chain.  The greatest most powerful camera will not be effective if the image is compressed down to nothing by the DVR.  The two most popular DVR resolution types are CIF and D1.  CIF is defined as 320×240 pixels and D1 is 720×480.  As you can tell, D1 is 4 times larger than CIF.  That means that the raw analog signal of the camera will be compressed less, giving you better detail.

When looking for a DVR keep recording resolution in mind.  Most DVRs have both options but will usually lower the frame rate to allow for higher resolution.

CCTV Resolution for IP Cameras

Next, we’ll cover CCTV resolution for IP cameras.  IP cameras (megapixel specifically) are able to deliver a much higher resolution.  Firstly, a MP camera is already digital so there is neither conversion nor compression.  Secondly, MP cameras run their signal through Cat 5 or 6 which allows for a much higher transfer of data.

1.3M is generally the smallest resolution of IP megapixel camera, but is still quite a bit larger resolution than any analog cam.  Even though this is a huge jump from analog, if this is not enough you can jump to 3.0 megapixel and get a 2048×1536 resolution.  Still want bigger?  Go with the 5 megapixel for a 2592×1944 for a HUGH image.

If analog resolutions are not cutting it for you, IP surveillance cameras can definitely accommodate any large resolutions.

Summary

 With a DVR and analog cameras you are limited to CIF, 2CIF, 4CIF, and D1 resolution.  This may or may not fit your specific needs for your CCTV setup.  If you need higher resolution you should consider IP megapixel cameras and a network video recorder.