Ok, so he just about tolerates the light going dim and bright again, forcing his irises to compensate, but now he's on the phone saying how he had a headache from watching last night's game through a wavy screen (he being one of those who follows football with obsessive fanaticism).
Two main issues are at play with entertainment devices, switching spikes and over voltage (so seldom is under voltage a problem we thought we'd leave it out).
It appears that designers of visual display units (VDUs), and this encompasses television sets, computer monitors, cctv screens, etc., have a strong certain belief that the mains is nothing other than a perfect sine wave. This is possibly because such development areas have big filtering systems to stop any 'harmful' radiation from what's being tested getting out. Unfortunately, nothing gets in either and the designer on the inside is never exposed to this.
Spikes from switching devices (motor controllers etc.) that exist on the mains can easily find their way through to the circuitry beyond the power supply through capacitive coupling through the power transformers, this is if their are any. The internal circuitry of television sets runs directly off mains voltage.
Most entertainment devices also don't have an earth to drain any extraneous currents, so the use of a filter on the mains input is pretty close to, well, useless! Computer and cctv monitors are usually supplied through isolated power supplies that are filtered to earth although, if the spikes that are large enough, could find their way back to sensitive inputs and disturb any picture being displayed.
LCD computer monitors appear to be vulnerable to this and have been seen to go blank for a second or so while the circuitry adjusts and 'locks' again to the various sync pulses.
One would think that modern technology (i.e. the newer television sets) were less affected by the power source. As is, many are now capable of operating from less than 100VAC to more than 250VAC, and either at 50 or 60 Hz making them truly "world-wide capable". Not so! It appears the more modern the technology, the less it appears to cope with "life's little knocks".
Over voltage can also create weird effects on VDUs. Some can even create the same effects as spikes. If their is one thing we hammer at throughout this book is 230VAC is actually a running voltage of 325V once rectified. Although the equipment will be tested for a higher voltage, it has a limit before the circuitry is stressed.
The stresses can sometimes be catastrophic, with components failing, but they usually manifest themselves as disturbances and can chase the PQ investigator up the wrong path (and up the wall too!).
The PSUs in VDUs are usually synchronised such that the PSU oscillates at the sweep frequency. This done to stop constantly changing magnetic effects that could cause waver or flicker. There is, however, a natural oscillating frequency and this can change with respect to the incoming voltage.
At a slight, but related tangent; Ripple exists in all rectified circuits, and Switch Mode Power Supplies are no exception. The ripple being determined by the size of smoothing capacitor vs. the current being drawn by the switching circuit. This voltage will rise and fall 100 times a second (120 in 60Hz countries).
Taking the fact that the natural oscillating frequency of the switch circuit can change with the incoming voltage, and that the voltage presented to it rises and falls by twice the mains frequency, during the peak of the wave form the switching frequency may approach that where it can no longer be synchronised to the sweep frequency. For that brief moment there will be unsynchronized magnetic fields which will disturb the cathode ray tube. These disturbances appear as "rolling bars" up or down the picture, especially if the frame rate is close to the mains frequency. Should the incoming voltage be even higher, the oscillation may never synchronize and could result in flicker.
General over-voltage issues with PSUs are discussed later. These could also manifest themselves as visual disturbances on entertainment systems.
There is one disturbance that is usually not related directly to PQ but has been found to be the cause of a number of complaints and investigations. The issue is that if "shimmering" displays. This is prevalent only in the Cathode Ray Tube type monitors and screens as their basic mode of operation is magnetic.
These suffer disturbance through two main issues being uncontrolled magnetic fields, or simply close proximity to conductors carrying high currents. It is going to be easier to tackle the latter subject first!
When designing buildings the main objective is to hide all ugly looking necessities such as large cables. These tend to run in voids within large columns, or even lift (elevator) shafts, with access made to them as and when required. The problem is these very same voids make nice corners and desks and TVs manage to make their way into them. Because the conductors are not wrapped round each other there is a rather large magnetic field within a few metres of these, and distinctly large enough to shimmer any CRT based VDU.
Even overhead power lines can affect such devices, up to many metres away. The higher the voltage the worse the problem as the spacing between the conductors is larger therefore less cancellation of the magnetic fields. Office blocks near power lines are not worthy of being considered if the office is to be mainly hi-tech with many VDUs, unless the expense of LCD monitors can be accommodated (except the lines would also affect telecoms, so there are two fronts to worry about).
The more complex issue of shimmering screens is uncontrolled magnetic fields. These are as a result of current flowing in metal structures rather than through the wiring. Other causes could be ring circuits with a broken connection on one of the legs. This would result in current flowing on one leg not being cancelled by the same current that should be flowing in the other leg.
Determining such magnetic fields are rather easy with the aid of a loop of about 200 turns on a former of about 50mm diameter, this then fed into an audio amplifier. This is covered in more detail in the section on "using instruments".
The final part of this section relates to audio disturbances on entertainment systems. Should the disturbance be hum related then consult the section on "leakage". This section deals with crackling.
Crackling heard on radios and television sets is as a result of arcing or corona. If arcing, this could be the occasional crack or a permanent buzz. Tracing such a fault can be tedious and it may prove prudent to read the section on "using a portable radio".
Other forms of crackling are as a result of corona, usually from the tips of connections or other sharp points. A case in question was an entire residential area of approximately 500 metres radius was having "snowy lines across the TV accompanied with a buzzing audio". The culprit was a piece of wire that had been thrown over a nearby 132kV line (probably in an attempt to recreate the big bang!) but had lodged on the line in a V-shape. When retrieved it was measured and from the fold to one tip was very close to ¼-wavelength of the frequency of the TV channel affected (Marconi lives on!).
Was this a PQ issue? Most certainly, as it was directly related to the quality of the line. Although it was not so in this but it could have been indicative of a breaking down connection. It sure had a few PQ investigators running around until yours truly showed up.
Usually a symptom in hi-fi and audio-visual equipment, buzzing audio is often a symptom of the use of a referenced ground. It is derived from the Neutral by some means of leakage, usually in the form of a small capacitor or high resistance. This method is often used for economic reasons (saves on a 3-pin plug, earth wiring, etc.) and to eliminate ground loop currents.
If more than one device is used (Hi-Fi amp, CD player, etc.), then, as long as all references are equal then all is ok. By using 2-pin plugs, the mains input is easily swapped and should one device be the wrong polarity, or the devices are some distance apart and fed from separate supplies, then these leakage currents flow along the signal ground.
The effect is usually nothing more than a disturbance of some nature and is often cured by swapping the 2-pin plug 180º (yes, it does become a challenge to know which plug to invert!). A further complicaton is high frequency noise present on the mains flows more readily through capacitive created reference grounds.
Referenced grounds are not only used in domestic entertainment, but in quite a lot of professional gear too. Such grounds are discussed later, and cures for disturbances from such grounds in the Solutions chapter of this book.
The moment alternating current hits the scene then frequency becomes a component. This is true of all electrical signals from (but not exclusively) mains through to satellite systems (i.e. a few Hz to many GHz). What is not commonly known is there are sometimes many frequencies used to achieve a single function.
Take a satellite receiver/decoder. At the dish is a unit converting many GHz to a few hundred MHz. Inside the receiver this is converted to a few MHz (it is, in effect, a television receiver). It is again converted to a few hundred MHz for transmission to the TV, but also uses approximately 32kHz for the remote control.
Just above this decoder is a low voltage lighting 'transformer' (which is actually a switch-mode power supply) and has a working frequency (or an harmonic) of just one of the multitude of frequencies used within the decoder. The decoder picks this up and tries to process this rendering it useless (only while the lighting transformer is on). The transformer is blamed, but in actual fact it is purely a case of incompatibility.
Granted, there are times when it the 'transformer' might not be operating to specification or design. As it is based on an oscillator there is a high possibility of parasitic oscillations that may be many times the operating frequency. If running at e.g. 100kHz, there is nothing saying a parasitic oscillation (ringing) could not exist at many tens of MHz. Changing the unit may well remove the 'jamming', but the new unit may just simply be emitting a non-problematic spurious signal.
But the problem is not only limited to spurious emissions. A similar problem could exist with a low voltage lighting supply operating at (or very close to) that used for the remote control (I specifically chose the remote as this is coupled by light to the device being controlled). Incandescent lamps emit more infrared than visible light (yes, that's why they get so hot!). All that is now needed is a reasonable amount of emitted infrared at the working frequency of the remote and the remote control is rendered inoperative.
It must be said that there are many such cases and we have covered but a fraction of the causes. However, this starts falling out of the realms of power quality as this sort of 'jamming' tends to happen beyond or outside the mains wiring. It was included here to show how easily such a case can be deemed a power quality issue. The only common factor is the mains provides power to both units!
"sometimes it's just physics that gets in the way"
Often overlooked by manufacturers of entertainment equipment is that the mains supply is by no means perfect. Often forgotten is that the smoothing capacitor is only topped up 100 times a second (120 in 60Hz countries). This means there is a distinct possibility audio and video output can be modulated by the power supply.
Furthermore, the fact there are long lines feeding the power supply i.e. inductive, higher frequencies have a clear means of being injected onto the mains. The fact aud frequencies can now exist on the mains means they canfind their way into other pieces of equipment such as a mixer. This type of effect is very real and is prevalent in networks at large venues, although such disturbances can also be seen on home entertainment.
This is not a power quality issue except that this is more a case of the load causing power quality degradation.