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Changes in the DC power supply can affect an A/D converter's accuracy. Power supply deviations can cause changes in the positive full-scale value, resulting in a proportional change in all the code transition values (i.e., a gain error). As a general rule, regulated power supplies with 1% or less ripple are recommended. Power supplies should be bypassed with a capacitor -- e.g. 1 to 10 µF tantalum -- located near the A/D converter, to get noise-free operation. Noise and spikes from a switching power supply must be carefully filtered. To reduce jitter effects, accurate crystal clocks must be used to clock all A/D as well as sample-and-hold circuits.

At data-acquisition, we recommend a two-tier approach to cleaning power:

Tier 1: For PCI DAQ boards, make install an excellent power supply in the computer.

The Turbo-Cool 510 ATX is an example of a very high-quality power supply. Here are its features:









A good PC power supply is one whose engineers have opted for really tight regulation and much cleaner power by using bigger capacitors to filter the DC output onto a much cleaner output than what the other manuf. had. These capacitors cost more. The Turbo-Cool uses triple-stage capacitors. On the input side, where one is converting the AC to DC, it also also uses bigger capacitors, and the effect of that is that it is able to better handle sags and surges and basically has a better holdup time. Rather than the typical 10 milliseconds, which is what most power supplies were doing, the Turbo-Cool is producing power for as much as 300 milliseconds. People notice when they had Turbo-Cool products and when the lights would dim and the blackouts would occur, they’d look around the room-- like a student’s room or a university or school where they had 10 or 20 computers -- and notice every single one of them was down except for the ones powered by Turbo-Cool. Most outages are anywhere from 10 to 300 milliseconds. So if you can give people enough capacitance to ride through that, you save a lot.

The heavy-duty Turbo-Cool® 510 power supply. Can power any single CPU system with up to twelve drives, the Turbo-Cool® 510 is the industry’s undisputed heavyweight champ.

* 510W (650W peak) @ 50°C (industrial rated)
* 2X more actual power than "500W" home PSUs
* Heavy-duty caps, inductors, heat sinks, etc.
* Extended sag and surge protection (.99 PFC)
* Powerful +12VDC output (34A, 38A peak)
* Ultra-tight voltage regulation (+VDC@ 1%)
* Super-clean output (+VDC ripple @ 0.5%)
* New, quieter fan speed control circuit
* Designed for ATX M/Bs with 20-pin connector

DC Output
Output: +5V @ 40A
+12V @ 34A/38A
-5V @ 0.3A
-12V @ 2A
+3.3V @ 30A
+5VSB @ 3A
continuous = 510W
peak = 650W
Regulation: 1% (+3.3, +5, +12)
5% (-5, -12)
Ripple: 0.5% (p-p)
Hold Time: 20ms
PG Delay: 300ms

AC Input
Operating Range: 90-264 VAC
.99 power factor
auto-select
Frequency: 47-63Hz
Current: 10A @ 115V
Efficiency: 70%
EMI: FCC-B, CE

Tier 2: The power going into the computer should be clean. Some uninterrupted power supplies (UPS) perform a little bit of power conditioning. But it's best to purchase a separate line conditioner. Several companies that specialize in audiophile, videophile and home-theater "power cleaning" offer such high-quality devices. Here at data-acquisition.us, we use Chang Lightspeed line conditioners, and place them after our UPS.



More info on power-line filtering:

Power-line filters remove impurities and artifacts from the alternating current (AC) that enters a computer or other sensitive electronic equipment. In addition, power-line filters protect equipment from potentially damaging voltage surges.
Power-line filters are not all the same. In fact, most are designed for computer applications and consequently do not satisfy the more stringent requirements needed for high-precision DAQ.
The ideal power-line filters satisfy the following performance criteria:
1. It must protect connected components from the potentially damaging effects of voltage surges. Sensing circuitry monitors AC voltage levels and "clamps" excessive voltages thus preventing them from reaching and damaging DAQ and computer components.
2. It must reduce pre-existing AC interference without adding any artifacts of its own. Even when compared to pure 60 Hz AC power available only under laboratory conditions (or 50 Hz where applicable), the ideal filter would not impose any performance restrictions at all. In fact, the increased component-to-component isolation offered by well-engineered power-line filters will improve A/D and D/A performance.
3. It must improve performance in direct proportion to the level of power-line contamination. Some (lower-quality) power-line filters have the same effect regardless of where they are used because they impose performance anomalies on any connected component.
4. It must deliver current instantly. This is in sharp contrast to the time lag between current demand and current supply always exhibited by conventional power-line filters. The power-line filter should not impose any current-delivery limitation or hesitation.


The irony of alternating current (AC)

The same AC that powers all electronic components is also a hindrance to optimum performance. Quite simply, AC power is not pure; it is contaminated by numerous and often-unavoidable sources of interference.
A mild case of blood poisoning will not stop a person from functioning but the accompanying low-grade fever will certainly prevent that person from performing at a high level. In an analogous way, sophisticated electronic components fed with contaminated AC power will still function but at a level far below their peak potential. Research scientists, engineers and computer professionals have known this for decades. This is why they protect and enhance the performance of their delicate and expensive equipment with devices providing AC power filtration that effectively removes power-line contaminants.
Power-line contaminants are many and varied. Unfortunately, they are also extremely common -- in fact, almost ever-present.

Problem 1: Voltage Surges
Instantaneous voltage surges in the AC line, sometimes reach into thousands of volts. In worst cases, these spikes first destroy component power supplies and then cascade to burn out all major circuitry blocks. Repairing the resultant catastrophic damage is always difficult and usually economically foolish as repair costs often exceed the original purchase price. A decent UPS/surge-protector provides good insurance against high-amplitude voltage spikes.
Lesser surges, far more common, are particularly troublesome for digital components due to the almost universal use of integrated circuits (ICs) in critical circuit paths. Although ICs allow unparalleled design freedom and cost reduction, they are also more voltage sensitive than discrete components. The result: Very minor voltage disturbances, even power-line transients produced when a refrigerator compressor turns on or off, can reduce the accuracy of A/D and D/A converters.
Lowest-level voltage surges appear as a near-continual "hash" in the power-line. Produced primarily by any running motor (air filter, hair dryer, etc.), this noise doesn't overtly damage components but wreaks havoc on sensitive digital components, such as DAQ boards and computer CPUs. Worst of all, power-line hash is virtually never-ending. Even if you're not running a motor in your household, rest assured that your neighbor (whether next door or blocks away) is!

Problem 2: RFI and EMI
We live in the age of wireless communication. Like most technological blessings, this one has an accompanying curse. Radio and microwave broadcasts literally engulf us. Our skies are jammed. In some areas, AM stations appear as background interference on audio systems and televisions. Cellular phone service "bleeds" through other transmissions. In short, signal interference is a major concern.
Your home/office AC line is not immune. In fact, RFI (radio frequency interference) often corrupts the AC current going to your sensitive components. Although not usually dangerous to your computer/DAQ system's long term reliability, this interference constantly robs you of the performance potential you've paid for.
The situation is indeed bleak; AC line purity is getting worse as technology proliferates. Bluntly stated, if AC power were water, your DAQ components would be drinking from a sewer!

Resources:

Chang: http://www.changlightspeed.com/
Turbo-Cool: http://www.pcpowercooling.com/products/viewproduct.php?show=T51ATX&view=about