Received signal strength indication (RSSI)

       In telecommunications, received signal strength indicator (RSSI) is a measurement of the power present in a received radio signal.

      RSSI is a generic radio receiver technology metric, which is usually invisible to the user of the device containing the receiver, but is directly known to users of wireless networking of IEEE 802.11 protocol family.

     In an IEEE 802.11 system RSSI is the relative received signal strength in a wireless environment, in arbitrary units. RSSI is an indication of the power level being received by the antenna. Therefore, the higher the RSSI number (or less negative in some devices), the stronger the signal.

Reference : http://en.wikipedia.org/wiki/Received_signal_strength_indication

Accuracy Class

Accuracy class tells the percentage error of an equipment.
For example, an Accuracy Class 1.0 CT means the error will be +/- 1 %. That means, say, you have a 100/5A CT and when you pass 100A through the primary of this CT, the secondary current can be anywhere between 4.95A to 5.05A.
The accuracy class stating the limits of permissible error is expressed as a percentage of the span.
The following accuracy classes are defined: 0.1, 0.25, 0.6, 1,1.6, 2.5 and 4.

Accuracy class Limits of permissible error                       (percentage of span)

0.1                                                                                     ± 0.1 %
0.25                                                                                   ± 0.25 %
0.6                                                                                     ± 0.6 %
1                                                                                        ± 1 %
1.6                                                                                     ± 1.6 %
2.5                                                                                     ± 2.5 %
4                                                                                        ± 4 %

Parameters for Effective Circuit Protection Using TVS

A good TVS device for protecting dataline communications interfaces must have some key parameters. 

First, low working voltage is a critical TVS parameter for safeguarding submicron integrated circuits. The working voltage, or Vrwm, is the maximum rated DC voltage for the TVS device. At the Vrwm voltage, the TVS is still a non-conducting device. Once the transient voltage rises above the working voltage, the TVS quickly achieves breakdown and presents a low impedance  path to divert the transient. Thus, a low working voltage is essential for clamping a transient to a level well below the damage threshold of the IC that the TVS is protecting. The I-V curve illustrates the advantage of a lower working voltage. The green line represents a typical  I-V curve for a standard TVS device. The lower working voltage means the transient voltage is arrested more quickly and thus can be clamped to a lower voltage. Using TVS devices with lower working voltage is critical to reducing the stress energy seen by the communications transceiver. 

Secondly, the TVS should present low capacitance to preserve signal integrity on the high-speed interface. If the capacitance of the TVS diodes is too high, adding excessive loading to the circuit, signal distortion and data errors will result.

Finally, the TVS needs to offer high-surge handling. For systems in the communications infrastructure, components rated only for ESD transient levels will not provide sufficient protection. The TVS component must also be able to handle the higher energy contained within cable discharges and the variety of lightning threats. As a general guideline, the TVS should at least provide 25A of surge handling for an 8x20 microsecond pulse. 

What is EMI and EMC ?

• An electromagnetic disturbance which may degrade the performance of an equipment (device, system or sub-system) or causes malfunction of the equipment, is called electromagnetic interference (EMI).

• Electromagnetic compatibility (EMC) is a near perfect state in which a receptor ( device , system or subsystem) functions satisfactorily in common electromagnetic environment, without introducing intolerable electromagnetic disturbance to any other devices / equipments / system in that environment.

Board Zoning

Board zoning has the same basic meaning as board floor planning, which is the process of defining the general location of components on the blank PCB before drawing in any traces. Board zoning goes a little bit further in that it includes the process of placing like functions on a board in the same general area, as opposed to mixing them together (see Figure). High-speed logic, including micros, are placed close to the power supply, with slower components located farther away, and analog components even farther still. With this arrangement, the high-speed logic has less chance to pollute other signal traces. It is especially important that oscillator tank loops be located away from analog circuits, low-speed signals, and connectors. This applies both to the board, and the space inside the box containing the board. Do not design in cable assemblies that fold over the oscillator or the microcomputer after final assembly, because they can pick up noise and carry it elsewhere. 

In prioritising component placement, the most important things to do in PCB design are:

• Locate the microcomputer next to the voltage regulator, and the voltage regulator next to where  the input power enters the board.


• Built a gridded or solid ground between the three 

Zarro boogs

By design, Bugzilla is programmed to return the string "zarro boogs found" instead of "0 bugs found" when a search for bugs returns no results"Zarro Boogs" is a facetious meta-statement about the nature of software debugging. Bug tracking systems like Bugzilla readily describe how many known bugs are outstanding. The response "zarro boogs", is intended as a buggy statement itself (a misspelling of "zero bugs"), implying that even when no bugs have been identified, software is still likely to contain bugs that haven't yet been identified.

The following comment is provided in the Bugzilla source code to developers who may be confused by this behaviour:

Zarro Boogs Found

This is just a goofy way of saying that there were no bugs found matching your query.

So when you query for a list of bugs, and it gets no results, you can think of this as a friendly reminder. Of *course* there are bugs matching your query, they just aren't in the bugsystem yet...

http://en.wikipedia.org/wiki/Zarro_boogs?useFormat=mobile#Zarro_boogs

Via Types

Through via : An interconnection between the top and the bottom layer of a PCB. Through vias can also provide interconnections to inner PCB layers.

Blind via : An interconnection from the top or bottom layer to an inner PCB layer.

Embedded via: An interconnection between any number of inner PCB layers.

Figure shows all three via types.