Selecting the Right Power Protection for Laboratory Instrumentation
The use of an uninterruptable power system (UPS) protects ?sensitive laboratory equipment from power anomalies.
Most laboratory professionals understand that it is imperative to follow the instructions in the manufacturer’s site preparation guide to avoid system malfunctions and maximize the throughput and productivity of custom-designed testing systems, sequencers, gas chromatograph/mass spectrometers (GC/MS), and other scientific instruments. However, there are a number of other important issues that they must address before their new equipment arrives to assure smooth implementation.
One of the most vital issues is to assure that the lab’s AC power is clean and stable to power the new equipment. There is often a common assumption that AC power coming from the wall outlet is reliable. It is only when one experiences a catastrophic power event that one becomes aware of the precarious nature of the power grid. Damaging power anomalies, such as harmonics, high voltage transients, and surges, while not as obvious as blackouts, can cause serious equipment performance and reliability problems.
To protect equipment from these costly power problems, many equipment manufacturers specify the use of an uninterruptible power system (UPS). The IEEE defines UPS topologies in the following categories: off-line, line-interactive (hybrid), and dual-conversion on-line. Due to the sensitive nature of lab instruments, a dual-conversion on-line UPS is the best choice since it solves the widest spectrum of power problems. Line-interactive and off-line UPS, while more economical, do not provide the high level of power protection and conditioning demanded.
Dirty and distorted power wreaks havoc with sensitive lab equipment (left). Noise, voltage drop-outs, and distortion have been completely removed by the on-line UPS (right). Only pure sine wave power is being supplied continuously by the UPS output. Images: Falcon Electric, Inc.
A dual conversion on-line UPS regenerates totally new sine wave power both in utility and battery backup modes. It converts the incoming AC power to DC, then filters and regulates it, and finally regenerates clean, new, tightly regulated AC power. This active approach assures superior ±2 to 3% output voltage regulation and provides the highest level of power conditioning demanded by sensitive laboratory equipment. Additionally, in contrast to off-line and line-interactive UPS designs, the on-line UPS only uses battery power when utility power is not present. Therefore, battery life is typically much longer than other UPS topologies. The on-line UPS has no disruptive switch-over drop when utility power is lost or restored. Most new on-line UPS also provide input power factor correction. This greatly reduces harmonics that may adversely affect building wiring and other equipment operating inside a lab.
Finally, another feature available with some on-line UPS is galvanic isolation. This eliminates neutral-to-ground and common mode noise paths, as well as ground loops, by electrically isolating the instrument to increase accuracy and data communications reliability. In most cases, an on-line UPS will solve the power problem, but if the issue is due to faulty wiring, this extra measure will address the absence of proper grounding in the area.
Selecting an on-line UPS
Rosetta Inpharmatics, Seattle, Wash., develops and implements technologies to improve drug discovery. The company’s scientists perform DNA testing utilizing highly sophisticated equipment, which is very sensitive to even the slightest power glitch. These systems must be protected against all power quality problems from the utility grid including brownouts and blackouts caused from weather-related problems. Rosetta’s R&D engineers designed and built several pre-production prototype machines that could synthesize DNA sequences onto glass wafers. Each section of DNA was deposited onto the wafer in differing colors using an inkjet print head. The researchers needed to produce many of these wafers in the daily course of their specialized research. Several inkjet synthesizer (IJS) machines were constructed to meet these wafer requirements and had to continuously operate 24 hours a day, seven days a week.
“We discovered that one of the IJS operation failure modes was the direct result of the utility-supplied power,” says William Hodgson, an electrical engineer at Rosetta Inpharmatics. “To combat this problem, we installed a 650 VA/400 W commercial-grade switching, or off-line UPS, that could provide approximately 6.6 min of backup power under full load.” However, the IJS systems continued to fail due to power line spikes and brownouts. The power faults passed directly through the off-line UPS, resulting damage to IJS systems.
The losses incurred by IJS failures were significant. “A primary determining factor was the safety issue,” continues Hodgson. “Power line faults that may cause the loss of chemical control is a significant issue, and management demanded immediate correction of any issues that adversely affected the safety of their personnel or the public in general.” In addition, more than seven power anomalies were detected during a one-year period that resulted in the shutdown of all IJSs.
“We needed to find a UPS system that could provide our IJS systems with continuous, clean power,” continues Hodgson. “The new UPS selected would have to be reliable in order to guarantee normal IJS operation without interruption, through any power anomaly.”
After considerable research, the Rosetta researchers determined that they needed a dual-conversion, on-line UPS system to handle the many power quality and interruption problems they were experiencing. Its battery is connected directly to the DC stage where the battery supplies power when the AC utility power is lost. Because there are no battery switch-overs or relays involved, there is no dead time or lost UPS output. In addition, power disturbances are completely filtered out with the newly regenerated UPS AC output. The on-line UPS also offers superior voltage regulation.
The IJS 900-W line power requirement was met using a UPS with a 1.5-kVA output rating. One reason for selecting the 1.5-kVA UPS instead of a 900-VA model was due to the need to include power factor into the calculation of the power. More than half of the IJS load consisted of a transformer isolated (inductive) linear power supply load. The remaining load consisted of the switching (capacitive inductive) power supply loads. This reduced the overall power factor. The run-time at full-load for a 1.5-kVA UPS was a typical 11 min. But the typical half-load run-time was almost three times the full-load. A UPS with a higher capacity would guarantee normal IJS operation through 100% of the power line disturbances that had occurred during the one-year period. And the larger capacity rating would translate into longer UPS life.
Based on these requirements, Hodgson selected the SG Series on-line UPS from Falcon Electric, Inc., Irwindale, Calif., that featured 115-VAC input and a rating of 2 kVA, 1400 W. Since the installation of the Falcon UPS, Rosetta has experienced line faults and even a 6.9 magnitude earthquake. “Riding through the earthquake was a true testament to the unit's reliability and quality,” says Hodgson. “Since the installation of the Falcon on-line units, Rosetta’s IJS systems have operated without failure during power line anomalies.”
Respecting power quality
The science of power quality is often not understood by the layman. In the case of power protection for R&D and laboratory applications, this lack of knowledge can prove very costly. Though commercial-grade off-line and line-interactive UPS work with office computers, they are totally incompatible with the demands of sensitive automated testing systems, laboratory equipment, and instruments. As such, the investment in a true on-line UPS with galvanic isolation will pay dividends for years to come.
—Paul Newman Director of Manufacturing Engineering, Falcon Electric, Inc.
