Electronics Engineering

In a properly operating appliance, there is no connection between any of its internal wiring and its chassis and/or its metal case, if there is one. As such, the earthing connection being improper will not affect the operation of the appliance.

However, and this is critical, an improper earthing connection can present an electrocution hazard to the user...

If the earth connection were electrically live or "hot", for instance, then the chassis of the appliance would also become live or "hot". Touching it, along with a real earth connection such as a water faucet, could cause electrocution.

Additionally, if the earth connection is simply missing, then an internal malfunction within the appliance could cause the chassis and/or its metal case, if there is one, to become live or "hot", creating the same risk of electrocution.

The purpose of the earthing connection is - in the event of appliance malfunction - to cause a high enough fault current that will force the protective device (fuse or circuit breaker) to trip and break the supply of current to the appliance.

In any semiconductor (doped or not) vibrations of the atoms in the crystal can sometimes knock electrons out of the atom's valence band into the conduction band. When this happens the electron now in the conduction band is added to the population of electrons in the semiconductor, while the void it left behind in the valence band is added to the population of holes in the semiconductor. As the vibrations that cause this generation of electron and hole pairs are usually thermal (although there are other causes too) they are usually called thermally generated electrons and holes.

Since the electron and hole pair are in close proximity when formed, many of them recombine before they could be separated by an electric field in the crystal or by simple diffusion.

There is of course a somewhat more complicated (but also more correct) explanation using Quantum Mechanics, but the above is sufficient to understand it at the first approximationlevel.

Analog phone lines. Analog signals. Digital security. Digital PBX. Analog-to-digital adapters. What does it all mean? In the telecom world, understanding analog versus digital isn't as simple as comparing one technology to another. It depends on what product-and in some cases, which product feature-you happen to be talking about. Analog at a glance

As a technology, analog is the process of taking an audio or video signal (in most cases, the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of "1"s and "0"s. Simple enough when it's the device-analog or digital phone, fax, modem, or likewise-that does all the converting for you. Is one technology better than the other? Analog technology has been around for decades. It's not that complicated a concept and it's fairly inexpensive to use. That's why we can buy a $20 telephone or watch a few TV stations with the use of a well-placed antenna. The trouble is, analog signals have size limitations as to how much data they can carry. So with our $20 phones and inexpensive TVs, we only get so much. Enter digital

The newer of the two, digital technology breaks your voice (or television) signal into binary code-a series of 1s and 0s-transfers it to the other end where another device (phone, modem or TV) takes all the numbers and reassembles them into the original signal. The beauty of digital is that it knows what it should be when it reaches the end of the transmission. That way, it can correct any errors that may have occurred in the data transfer. What does all that mean to you? Clarity. In most cases, you'll get distortion-free conversations and clearer TV pictures. You'll get more, too. The nature of digital technology allows it to cram lots of those 1s and 0s together into the same space an analog signal uses. Like your button-rich phone at work or your 200-plus digital cable service, that means more features can be crammed into the digital signal. Compare your simple home phone with the one you may have at the office. At home you have mute, redial, and maybe a few speed-dial buttons. Your phone at work is loaded with function keys, call transfer buttons, and even voice mail. Now, before audiophiles start yelling at me through their PC screens, yes, analog can deliver better sound quality than digital…for now. Digital offers better clarity, but analog gives you richer quality. But like any new technology, digital has a few shortcomings. Since devices are constantly translating, coding, and reassembling your voice, you won't get the same rich sound quality as you do with analog. And for now, digital is still relatively expensive. But slowly, digital-like the VCR or the CD-is coming down in cost and coming out in everything from cell phones to satellite dishes. When you're shopping in the telecom world, you often see products touted as "all digital." Or warnings such as "analog lines only." What does it mean? The basic analog and digital technologies vary a bit in definition depending on how they're implemented. Read on. Phone lines

Analog lines, also referred to as POTS (Plain Old Telephone Service), support standard phones, fax machines, and modems. These are the lines typically found in your home or small office. Digital lines are found in large, corporate phone systems. How do you tell if the phone line is analog or digital? Look at the back of the telephone connected to it. If you see "complies with part 68, FCC Rules" and a Ringer Equivalence Number (REN), then the phone and the line are analog. Also, look at the phone's dialpad. Are there multiple function keys? Do you need to dial "9" for an outside line? These are indicators that the phone and the line are digital. A word of caution. Though digital lines carry lower voltages than analog lines, they still pose a threat to your analog equipment. If you're thinking of connecting your phone, modem, or fax machine to your office's digital phone system, DON'T! At the very least, your equipment may not function properly. In the worst case, you could zap your communications tools into oblivion. How? Let's say you connect your home analog phone to your office's digital line. When you lift the receiver, the phone tries to draw an electrical current to operate. Typically this is regulated by the phone company's central office. Since the typical proprietary digital phone system has no facilities to regulate the current being drawn through it, your analog phone can draw too much current-so much that it either fries itself or in rare cases, damages the phone system's line card. What to do? There are digital-to-analog adapters that not only let you use analog equipment in a digital environment, but also safeguard against frying the internal circuitry of your phone, fax, modem, or laptop. Some adapters manufactured by Konexx come designed to work with one specific piece of office equipment: phone, modem, laptop, or teleconferencer. Simply connect the adapter in between your digital line and your analog device. That's it. Or you can try a universal digital-to-analog adapter such as Hello Direct's LineStein®. It works with any analog communications device. Plus, it's battery powered so you're not running extra cords all over your office. Cordless phones

The very nature of digital technology-breaking a signal into binary code and recreating it on the receiving end-gives you clear, distortion-free cordless calls. Cordless phones with digital technology are also able to encrypt all those 1s and 0s during transmission so your conversation is safe from eavesdroppers. Plus, more power can be applied to digital signals and thus, you'll enjoy longer range on your cordless phone conversations. The advantage to analog cordless products? Well, they're a bit cheaper. And the sound quality is richer. So unless you need digital security, why not save a few bucks and go with an analog phone? After all, in home or small office environments where you may be the only cordless user, you won't have any interference issues. Keep in mind, when talking about digital and analog cordless phones, you're talking about the signals being transferred between the handset and its base. The phones themselves are still analog devices that can only be used on analog lines. Also, the range of your cordless phone-analog or digital-will always depend on the environment. Cellular phones

Perhaps the most effective use of the digital versus analog technology is in the booming cellular market. With new phone activations increasing exponentially, the limits of analog are quickly being realized. Digital cellular lets significantly more people use their phones within a single coverage area. More data can be sent and received simultaneously by each phone user. Plus, transmissions are more resistant to static and signal fading. And with the all-in-one phones out now-phone, pager, voice mail, internet access-digital phones offer more features than their analog predecessors. Analog's sound quality is still superior-as some users with dual-transmission phones will manually switch to analog for better sound when they're not concerned with a crowded coverage area-but digital is quickly becoming the norm in the cellular market. What to buy?

The first thing to consider when buying analog or digital equipment is where you'll be using it. If you're buying for a proprietary PBX phone system, you'll need to get the digital phone designed for that particular system. Need to connect a conferencer on your digital system? Opt for a digital-to-analog adapter. Shopping for home office equipment? Most everything you'll consider is analog. Want an all-in-one cellular phone-paging, voice mail, web? A digital cellular phone will deliver it all. In fact, the only head-scratcher may be your cordless phone purchase. Looking for security and distortion-free conversations in your small office? Go with a digital 900 MHz or 2.4 GHz cordless phone. Using a cordless at home? An analog phone will give you the richest sound quality and usually enough range.