by Garth Powell *
So far I have written about the unique likeness of each professional electronic installation, is the live sound, broadcast on radio and television, sports venues, nightclubs or automated audiovisual systems for boardrooms: all depend on the power supply by AC (AC). In the previous two articles we discussed the peaks and transients AC, the danger of multiphase power supply with noise problems and intermittent AC neutral, ground loops and compression power.
Some of these issues are crucial for each installation, while others only become important when the application guarantees interest in maintaining the highest levels of quality. For example, if we are supplying power to a computer system for an office or for a scenario full of high-quality power amplifiers and mixing consoles, we must protect the equipment and make sure we do not lose our programming. There is a fundamental need to protect and filter dangerous fluctuations of current and noise that would affect the basic operation of our equipment.
Other control technologies AC power are more specific depending on the application. There is no doubt that a boardroom will have no problem minimize compression power in its power amplifiers, since the quality of the audio to a slide show or seminar transmitted over the Internet does not require the highest resolution (unless is the boardroom of a record label).
However, in this respect there is another common concern to all applications in Latin America: the AC voltage regulation. In short, a voltage regulator adjusts the AC input voltage and corrects abnormally high or low voltages, feeding vital components with a constant stream of 120 VAC. While the voltage may be of some continuously in some areas of their city, state or country, it is important to understand that most of the equipment you specify were created for a constant supply of 120 VAC. Still, the average voltage in Mexico, to cite one example, is 127 volts. Although located within 10% of the optimum voltage components, this will raise the temperature of the power supplies of many commercial electronics.
Some vital components may experience significantly greater distortions (unless all circuit parameters programmed from the factory to be recalibrated 127 VRMS). And 127 volts is just the average What happens in 130 or 136 volts? the operation is affected. Some teams will be blocked or intermittently overheat due to abnormal increases in line voltage AC. In addition, abnormal low of less than 112 VAC voltage raise similar concerns. It may present the same phenomenon and intermittent greater distortions. For example, some video projectors can not receive a consistent supply under these conditions reduced voltage.
Of course, for many people in Latin America, this is not a startling revelation. Many electrical contractors and designers have spent years audiovisual systems using AC voltage regulators. But many of these units are bulky devices to maintain basic appliances and incandescent lights, installed behind a standby generator. Electronic devices today require much cleaner technology and stable regulation. Overvoltage regulator grandfather, with burnt and rusty rusty electrical contactors and high impedance circuits, creates the same amount of problems trying to solve in the current sensitive electronic circuits.
Many regulators brownouts can cause shock, create noise AC, significantly increase the impedance of the AC (severely limiting amplifier performance), or simply fail to handle the demands of running your AV system uncut form wave of the AC and adding distortions that adversely affect the image and sound quality. This is equally problematic for current microprocessing technologies, as these require a stable and clean source of AC power to prevent blockages, digital errors and loss of information.
It should be understood that various technologies have been developed for different applications. Control technology more practical voltage for lighting your home is not necessarily required for your video server, and the system would be ideal for machines large engines is not what would best for a rack of power amplifiers. Of the many technologies voltage regulator that are in the market, the most common are:
- ferroresonant: it is a complex circuit capacitance and inductance transformer modulated to create a substantially constant voltage and reduce noise asymmetric. The circuit is moderately expensive and can work well in some industrial or laboratory environments. Unfortunately creates heat, no tolerance for dynamic loads such as power amplifiers, emits a very audible hum and projects a magnetic field of several meters. For these reasons, it is not a control technology ideal for audiovisual professionals microprocessing circuits or computer systems.
- Amplifier / oscillator complete regeneration: essentially this is equivalent to a power amplifier with large oscillator operating 60 Hz input. Take the AC input voltage, direct current makes it synthesizes and then again a source of AC with low distortion. The advantage is exceptionally strong regulation (generally ± 0,1 VAC). It also reduces the distortion of the AC line and eliminates some of the symmetrical AC noise. Unfortunately, this technology is inefficient and costly end. A simple output capacity 10 amps can be worth several thousand dollars, reheat a whole enclosure and create serious distortions compressions current or AC signal when the capacity is exceeded. It is ideal for AC synchronous motors, not for professional audiovisual equipment.
- active correction lift / reduction: This design compares the AC voltage with a reference amplitude and controlled distortion, and adds or subtracts a correction to the AC input (with a maximum correction of ± 20%). The regulation can be very good (usually ± 0,5 VAC). It is much more efficient than complete regeneration to 100%, but may suffer from a serious limitation of current and AC create noise and distortion itself, partly due to the exchange of circuits that are commonly used. This technology might work well for some low current audiovisual equipment, but can be overcome by a autoformer several leads with solid state switching for its power amplifiers.
- Motorized Variac: This design uses a autoformer lift / reduction with various derivations. On the surface above a cut autoformer are exposed coils which contacts a brush, creating the appropriate AC voltage, either raising or lowering the voltage. A microprocessor constantly monitors the input voltage relative to the output voltage, and moves the wiper motor accordingly. This technology has good regulation (± 1 generally VAC), but has the disadvantage that the engine emits a very audible noise when placed in an area of audio. This technology was created for laboratories performing constant voltage readings.
Since the coils are covered with fat, and make contact with a brush, high current demands create sparks and noise in the AC line. The brush must be replaced and coils cleaned every one to two years. This makes the technology impractical for long-term use in most applications. In addition, the contactor creates a relatively high AC impedance, which seriously affects the power amplifiers. While industrial versions mass of this technology have been used for decades by some traveling professionals A / V (particularly when following a diesel generator and erratic voltage output) systems, low noise and ultra-high resolution today require much more of its energy source.
Finally, but by no means to forget, is my favorite technology AC voltage regulation for A / V professional, broadcast on radio and television, recording and boardrooms alike.
Autoformer switching zero crossing solid state with various derivations: this circuit works very similarly to motorized variac, except that as the microprocessor input and output (comparator) indicates the regulator circuit to raise or lower voltage. This is achieved by solid state switches with zero crossing. Since multiple switches are used, there is no exposed coils, and electrical contacts remain tight and secure for many years to come. The regulation can be quite good (± 3 VAC) with a reasonably wide capture rate (90 135 VAC-VAC). This circuit also has a control features exceptionally good transient compression with very little current. Unfortunately, the solid state switching can create some noise from AC if not precisely calibrated so that a good design without this noise can easily cost more than $ 700. However, if you have the budget, this is an excellent candidate for sensitive components today, even if they are subject to the most demanding environments.
Keep in mind that installations that depend on standby generators (gas or diesel) must be followed by a voltage stabilizer if you have a system that requires a corresponding voltage even at 120 volts. This is because the output voltage specifications of the generators are based on a constant current load. Does it look like any A / V system you have ever installed? Of course not. The result is that the current demand rises suddenly, the generator produces very little voltage and when the demand of low current, the generator produces too much voltage.
An AC voltage regulator is needed to control this. In addition, when a suitable AC regulator is combined with other energy control technologies, such as removing non-sacrificial surge and linear AC noise filtering, your system will be stable and secure, and your client will be well served.
*Garth Powell is a senior product designer and engineer sales chief Furman, a world leader in providing solutions for electrical control. It can be contacted at: email@example.com.