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News Release from: Advance Electronics | Subject: TVSS devices
Edited by the Engineeringtalk Editorial Team on 13 August 2002

Can TVSSs solve communications problems?

Mick Burgoyne, Chief Engineer at Advance Galatrek looks at how telecomms and data installations can benefit from the installation of the latest voltage surge suppression technology.

It's an all too familiar scenario You're on the phone to an important customer, and - far from being able to hear whether he's about to place the biggest order of the year - all you hear is an irritating crackling on the line

Worse still, your plea to repeat the last sentence for the third time just doesn't seem to be getting through.

Well, if it's any comfort at all, you are not alone.

Every year, thousands of users report that their critical business calls have suffered, for some inexplicable reason, from intermittent hissing, buzzing, crackling and general interference.

And, when the phone companies investigate the phenomenon, they find nothing untoward.

It's a phenomenon that frustrates IT departments, telecomms engineers, sales managers, directors - in fact anyone that has to use the phone on a regular basis for business.

But, this understandable annoyance that many of our industries suffer as a result of poor quality voice communications is nothing compared to the potential loss of revenue that can arise if their data systems suffer the same fate.

And yes, you'd better believe that this is exactly what all too many businesses are experiencing at this very moment.

But the worse thing, however, is most organisations are unable to attribute their voice and data processing errors to anything other than the occasional glitch.

Make no mistake, every click and crackle on the phone, as well as every PC crash or data error has a cause somewhere.

And, although I'm not suggesting that spikes and surges in the power supply are at the root of each and every problem, there is little doubt that they contribute to a significant number of these anomalies and aberrations.

In fact, no lesser source than IBM's Systems Development Division comments that: "More than 80% of mains power problems are transient and noise related".

On top of the annoyance caused by crackling and other interference on voice calls, many organisations suffer from more sinister problems and damage.

Many of us have used modems that, inexplicably, have refused to work one morning; usually we just shrug our shoulders, and attribute their failure to wear and tear.

Equally, some of us will have heard of phone systems that simply refuse to operate, even though they might have just been serviced.

Then again, there are countless stories of computer power supplies failing prematurely, network cards breaking down before their time and hard drives ceasing working, with the loss of vital data.

All these incidents have a cost implication, of course.

In the first instance, there is the obvious bottom line financial penalty associated with repairing, or more likely replacing, damaged equipment.

After all, many of these highly sensitive electrical components are performing essential tasks that cannot easily be switched to other equipment.

As such, business continuity will be severely compromised if the damaged equipment remains inoperable, even for a short duration.

As well as the physical cost of replacing damaged and broken components and equipment, there are the wider costs associated with critical system downtime.

For example, if an organisation's phone system is out of commission for even just a few minutes, who is to say which vitally important calls might have been missed during that time? Moreover, if data belonging to the company is damaged, erased or corrupted as a result of some power problem, there is the incalculable cost of trying to piece together what has been lost.

Given that many organisations do not possess back ups of their data, it is hardly surprising to hear that some companies never recover from such a disaster.

So, what's the real cause of these potentially business threatening problems and, equally, what remedies can we propose? Well, the first thing to remember is that there are many sources of electricity all around us.

Mains power, generated in the usual way and distributed to us via the national grid, is only one of the many ways in which electricity enters our daily lives.

Static electricity, generated by clothing for example, can wreak havoc with sensitive microchips and processors.

Even more destructive is the awesome power contained in a lightning strike.

As an example, a typical strike can lead to a voltage surge of well over 20kV being transmitted through the mains supply.

Not surprisingly, this can cause instantaneous and catastrophic equipment failure, resulting in immediate operational shut down and long term disruption of business.

Remember however that research indicates that up to 80% of voltage surges come from internal sources such as motors, fluorescent lights, photocopiers and other switching devices.

This leaves the remaining 20% of transients arising from external phenomena such as lightning.

Of course, this doesn't mean that either is more deleterious than the other.

In fact, even though internally generated transients will normally be of a lower peak voltage, they will often cause cumulative damage, leading to premature failure over a period of time.

It's just that external transients receive more publicity and interest, largely because they are more spectacular and, more often than not, the cause of immediate equipment failure.

So, the answer is some sort of component that can be placed before the critical component - be it comms or data hardware - that will successfully absorb and dissipate the transient energy from both internal and external sources.

But don't think that this is a problem that only affects the mains input.

There are plenty of documented instances of phones, modems, faxes and data servers being damaged by transient energy transmitted down the telephone line or communications cabling.

This is where the transient voltage surge suppressor - or TVSS - comes into play.

Briefly, a TVSS is a passive device that limits the amount of energy arising from a transient surge and, as a result, protects electrical equipment from damage.

Equally, however, a TVSS can also be used in circumstances where certain equipment known to produce transients - such as photocopiers - needs to be isolated from more sensitive hardware.

One of the most damaging events for the highly sensitive modern communications equipment that we all have in our offices and factories is a lightning strike actually hitting a telephone line.

Just as when lightning surges through a mains supply, the peak voltage produced can be in excess of 20kV.

Not surprisingly, the electronics contained in our telephones, faxes and modems cannot withstand this level of voltage spike, even for a few milliseconds.

What we need, therefore, is to install a transient voltage surge suppression module upstream of the comms hardware, in exactly the same manner as we would with a mains TVSS unit.

The same principle applies equally to data comms and cabling installations.

Imagine for a moment the likely consequences of several thousand volts coursing unchecked through the back of your PC, via your network connection, serial port or USB.

Even those of us with a less than vivid imagination will be able to foresee the makings of an IT disaster.

Fried motherboards, inaccessible hard drives and unusable memory would all be on the menu.

And, as I mentioned before, even though the actual replacement costs might just be containable, the longer-term consequences might not be surmountable.

Even if we disregard the effects of an average strength lightning strike on our data and comms hardware, there is still the more insidious effect of lower energy surges and spikes to consider.

Because transient energy has many sources, highly susceptible data and voice communications cabling can be subject to wide ranging variations in voltage.

In practice, this means that components that were designed to accept just a few millivolts can see many times their rated voltage, time and time again.

Over a period of time, this exposure to unwanted transients can lead to dramatically accelerated wear and tear, with the result that the design life of each critical component is significantly reduced.

And what's the consequence of this effect? Well, rather like the metal fatigue that sets in when a component is stressed beyond its design parameters, the electronics will inevitably suffer failure when you least expect it.

And the likely cost of such a failure? Again, if you value the data on your system, and have some inkling of what a full IT infrastructure crash could do to your organisation, you'll be able to answer that one yourself.

It's worth touching briefly on the types of TVSS that are commercially available.

There are three basic types of surge suppressor on the market - the gas discharge tube (GDT), the metal oxide varistor (MOV) and the silicon avalanche diode (SAD).

Each unit has its own characteristics, although the manner in which the individual components are assembled also affects the efficiency of the device.

Tests have indicated that a combination of SADs and MOVs provides the best overall solution.

Because the SADs react very quickly, they prevent the clamping voltage of the device rising as more current is dissipated by the MOVs.

The ideal component structure for a TVSS device is the matrix configuration.

This is an entirely passive solution, where the individual SADs and MOVs are arranged in separate assemblies, allowing individual components to self-sacrifice without compromising the performance of the TVSS as a whole.

Because of this, the matrix solution offers all the advantages of SADs and MOVs as individual components, but provides additional reliability and crucial performance where they are most needed.

Even if one of the SADs or MOVs should fail, the remaining components will continue to protect sensitive equipment from possible damage.

In fact, TVSS devices using matrix technology have an anticipated survival time of 100,000 lightning strikes, even allowing for individual component self-sacrifice.

And after all, there can be little doubt that the occasional replacement of a passive component such as a voltage surge suppressor is a far better option than risking your organisation's entire business in the event of critical component failure.

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